Re: [RFC v2 4/5] drm/dp: Extract i915's eDP backlight code into DRM helpers

[Rodrigo Vivi]

On Mon, Jan 25, 2021 at 07:10:30PM -0500, Lyude Paul wrote:
> Since we're about to implement eDP backlight support in nouveau using the
> standard protocol from VESA, we might as well just take the code that's
> already written for this and move it into a set of shared DRM helpers.
> 
> Note that these helpers are intended to handle DPCD related backlight
> control bits such as setting the brightness level over AUX, probing the
> backlight's TCON, enabling/disabling the backlight over AUX if supported,
> etc. Any PWM-related portions of backlight control are explicitly left up
> to the driver, as these will vary from platform to platform.
> 
> The only exception to this is the calculation of the PWM frequency
> pre-divider value. This is because the only platform-specific information
> required for this is the PWM frequency of the panel, which the driver is
> expected to provide if available. The actual algorithm for calculating this
> value is standard and is defined in the eDP specification from VESA.
> 
> Note that these helpers do not yet implement the full range of features
> the VESA backlight interface provides, and only provide the following
> functionality (all of which was already present in i915's DPCD backlight
> support):

This is definitely a good move.

Also the functions are well defined and well documented.

I noticed it wouldn't be straightforward, but I was wondering if it is possible to make the change in 2 steps (at least):
1. modify i915 code in place to match new functions
2. move to drm adding the documentation, proper returns etc....

I couldn't get a good sense of the changes around DPCD mode for instance.

> 
> * Basic control of brightness levels
> * Basic probing of backlight capabilities
> * Helpers for enabling and disabling the backlight
> 
> Signed-off-by: Lyude Paul <lyude@xxxxxxxxxx>
> Cc: Jani Nikula <jani.nikula@xxxxxxxxx>
> Cc: Dave Airlie <airlied@xxxxxxxxx>
> Cc: greg.depoire@xxxxxxxxx
> ---
>  drivers/gpu/drm/drm_dp_helper.c               | 332 ++++++++++++++++++
>  .../drm/i915/display/intel_display_types.h    |   3 +-
>  .../drm/i915/display/intel_dp_aux_backlight.c | 288 ++-------------
>  include/drm/drm_dp_helper.h                   |  48 +++
>  4 files changed, 413 insertions(+), 258 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_dp_helper.c b/drivers/gpu/drm/drm_dp_helper.c
> index eedbb48815b7..04cb2b6970a8 100644
> --- a/drivers/gpu/drm/drm_dp_helper.c
> +++ b/drivers/gpu/drm/drm_dp_helper.c
> @@ -3082,3 +3082,335 @@ int drm_dp_pcon_convert_rgb_to_ycbcr(struct drm_dp_aux *aux, u8 color_spc)
>  	return 0;
>  }
>  EXPORT_SYMBOL(drm_dp_pcon_convert_rgb_to_ycbcr);
> +
> +/**
> + * drm_edp_backlight_set_level() - Set the backlight level of an eDP panel via AUX
> + * @aux: The DP AUX channel to use
> + * @bl: Backlight capability info from drm_edp_backlight_init()
> + * @level: The brightness level to set
> + *
> + * Sets the brightness level of an eDP panel's backlight. Note that the panel's backlight must
> + * already have been enabled by the driver by calling drm_edp_backlight_enable().
> + *
> + * Returns: %0 on success, negative error code on failure
> + */
> +int drm_edp_backlight_set_level(struct drm_dp_aux *aux, const struct drm_edp_backlight_info *bl,
> +				u16 level)
> +{
> +	int ret;
> +	u8 buf[2] = { 0 };
> +
> +	if (bl->lsb_reg_used) {
> +		buf[0] = (level & 0xFF00) >> 8;
> +		buf[1] = (level & 0x00FF);
> +	} else {
> +		buf[0] = level;
> +	}
> +
> +	ret = drm_dp_dpcd_write(aux, DP_EDP_BACKLIGHT_BRIGHTNESS_MSB, buf, sizeof(buf));
> +	if (ret != sizeof(buf)) {
> +		DRM_ERROR("%s: Failed to write aux backlight level: %d\n", aux->name, ret);
> +		return ret < 0 ? ret : -EIO;
> +	}
> +
> +	return 0;
> +}
> +EXPORT_SYMBOL(drm_edp_backlight_set_level);
> +
> +static int
> +drm_edp_backlight_set_enable(struct drm_dp_aux *aux, const struct drm_edp_backlight_info *bl,
> +			     bool enable)
> +{
> +	int ret;
> +	u8 buf;
> +
> +	/* The panel uses something other then DPCD for enabling it's backlight */
> +	if (!bl->aux_enable)
> +		return 0;
> +
> +	ret = drm_dp_dpcd_readb(aux, DP_EDP_DISPLAY_CONTROL_REGISTER, &buf);
> +	if (ret != 1) {
> +		DRM_ERROR("%s: Failed to read eDP display control register: %d\n", aux->name, ret);
> +		return ret < 0 ? ret : -EIO;
> +	}
> +	if (enable)
> +		buf |= DP_EDP_BACKLIGHT_ENABLE;
> +	else
> +		buf &= ~DP_EDP_BACKLIGHT_ENABLE;
> +
> +	ret = drm_dp_dpcd_writeb(aux, DP_EDP_DISPLAY_CONTROL_REGISTER, buf);
> +	if (ret != 1) {
> +		DRM_ERROR("%s: Failed to write eDP display control register: %d\n", aux->name, ret);
> +		return ret < 0 ? ret : -EIO;
> +	}
> +
> +	return 0;
> +}
> +
> +/**
> + * drm_edp_backlight_enable() - Enable an eDP panel's backlight using DPCD
> + * @aux: The DP AUX channel to use
> + * @bl: Backlight capability info from drm_edp_backlight_init()
> + * @level: The initial backlight level to set via AUX, if there is one
> + *
> + * This function handles enabling DPCD backlight controls on a panel over DPCD, while additionally
> + * restoring any important backlight state such as the given backlight level, the brightness byte
> + * count, backlight frequency, etc.
> + *
> + * Note that certain panels, while supporting brightness level controls over DPCD, may not support
> + * having their backlights enabled via the standard %DP_EDP_DISPLAY_CONTROL_REGISTER. On such panels
> + * &drm_edp_backlight_info.aux_enable will be set to %false, this function will skip the step of
> + * programming the %DP_EDP_DISPLAY_CONTROL_REGISTER, and the driver must perform the required
> + * implementation specific step for enabling the backlight after calling this function.
> + *
> + * Returns: %0 on success, negative error code on failure.
> + */
> +int drm_edp_backlight_enable(struct drm_dp_aux *aux, const struct drm_edp_backlight_info *bl,
> +			     const u16 level)
> +{
> +	int ret;
> +	u8 dpcd_buf, new_dpcd_buf;
> +
> +	ret = drm_dp_dpcd_readb(aux, DP_EDP_BACKLIGHT_MODE_SET_REGISTER, &dpcd_buf);
> +	if (ret != 1) {
> +		DRM_DEBUG_KMS("%s: Failed to read backlight mode: %d\n", aux->name, ret);
> +		return ret < 0 ? ret : -EIO;
> +	}
> +
> +	new_dpcd_buf = dpcd_buf;
> +
> +	if ((dpcd_buf & DP_EDP_BACKLIGHT_CONTROL_MODE_MASK) != DP_EDP_BACKLIGHT_CONTROL_MODE_DPCD) {
> +		new_dpcd_buf &= ~DP_EDP_BACKLIGHT_CONTROL_MODE_MASK;
> +		new_dpcd_buf |= DP_EDP_BACKLIGHT_CONTROL_MODE_DPCD;
> +
> +		ret = drm_dp_dpcd_writeb(aux, DP_EDP_PWMGEN_BIT_COUNT, bl->pwmgen_bit_count);
> +		if (ret != 1)
> +			DRM_DEBUG_KMS("%s: Failed to write aux pwmgen bit count: %d\n",
> +				      aux->name, ret);
> +	}
> +
> +	if (bl->pwm_freq_pre_divider) {
> +		ret = drm_dp_dpcd_writeb(aux, DP_EDP_BACKLIGHT_FREQ_SET, bl->pwm_freq_pre_divider);
> +		if (ret != 1)
> +			DRM_DEBUG_KMS("%s: Failed to write aux backlight frequency: %d\n",
> +				      aux->name, ret);
> +		else
> +			new_dpcd_buf |= DP_EDP_BACKLIGHT_FREQ_AUX_SET_ENABLE;
> +	}
> +
> +	if (new_dpcd_buf != dpcd_buf) {
> +		ret = drm_dp_dpcd_writeb(aux, DP_EDP_BACKLIGHT_MODE_SET_REGISTER, new_dpcd_buf);
> +		if (ret != 1) {
> +			DRM_DEBUG_KMS("%s: Failed to write aux backlight mode: %d\n",
> +				      aux->name, ret);
> +			return ret < 0 ? ret : -EIO;
> +		}
> +	}
> +
> +	ret = drm_edp_backlight_set_level(aux, bl, level);
> +	if (ret < 0)
> +		return ret;
> +	ret = drm_edp_backlight_set_enable(aux, bl, true);
> +	if (ret < 0)
> +		return ret;
> +
> +	return 0;
> +}
> +EXPORT_SYMBOL(drm_edp_backlight_enable);
> +
> +/**
> + * drm_edp_backlight_disable() - Disable an eDP backlight using DPCD, if supported
> + * @aux: The DP AUX channel to use
> + * @bl: Backlight capability info from drm_edp_backlight_init()
> + *
> + * This function handles disabling DPCD backlight controls on a panel over AUX. Note that some
> + * panels have backlights that are enabled/disabled by other means, despite having their brightness
> + * values controlled through DPCD. On such panels &drm_edp_backlight_info.aux_enable will be set to
> + * %false, this function will become a no-op (and we will skip updating
> + * %DP_EDP_DISPLAY_CONTROL_REGISTER), and the driver must take care to perform it's own
> + * implementation specific step for disabling the backlight.
> + *
> + * Returns: %0 on success or no-op, negative error code on failure.
> + */
> +int drm_edp_backlight_disable(struct drm_dp_aux *aux, const struct drm_edp_backlight_info *bl)
> +{
> +	int ret;
> +
> +	ret = drm_edp_backlight_set_enable(aux, bl, false);
> +	if (ret < 0)
> +		return ret;
> +
> +	return 0;
> +}
> +EXPORT_SYMBOL(drm_edp_backlight_disable);
> +
> +static inline int
> +drm_edp_backlight_probe_max(struct drm_dp_aux *aux, struct drm_edp_backlight_info *bl,
> +			    u16 driver_pwm_freq_hz, const u8 edp_dpcd[EDP_DISPLAY_CTL_CAP_SIZE])
> +{
> +	int fxp, fxp_min, fxp_max, fxp_actual, f = 1;
> +	int ret;
> +	u8 pn, pn_min, pn_max;
> +
> +	ret = drm_dp_dpcd_readb(aux, DP_EDP_PWMGEN_BIT_COUNT, &pn);
> +	if (ret != 1) {
> +		DRM_DEBUG_KMS("%s: Failed to read pwmgen bit count cap: %d\n", aux->name, ret);
> +		return -ENODEV;
> +	}
> +
> +	pn &= DP_EDP_PWMGEN_BIT_COUNT_MASK;
> +	bl->max = (1 << pn) - 1;
> +	if (!driver_pwm_freq_hz)
> +		return 0;
> +
> +	/*
> +	 * Set PWM Frequency divider to match desired frequency provided by the driver.
> +	 * The PWM Frequency is calculated as 27Mhz / (F x P).
> +	 * - Where F = PWM Frequency Pre-Divider value programmed by field 7:0 of the
> +	 *             EDP_BACKLIGHT_FREQ_SET register (DPCD Address 00728h)
> +	 * - Where P = 2^Pn, where Pn is the value programmed by field 4:0 of the
> +	 *             EDP_PWMGEN_BIT_COUNT register (DPCD Address 00724h)
> +	 */
> +
> +	/* Find desired value of (F x P)
> +	 * Note that, if F x P is out of supported range, the maximum value or minimum value will
> +	 * applied automatically. So no need to check that.
> +	 */
> +	fxp = DIV_ROUND_CLOSEST(1000 * DP_EDP_BACKLIGHT_FREQ_BASE_KHZ, driver_pwm_freq_hz);
> +
> +	/* Use highest possible value of Pn for more granularity of brightness adjustment while
> +	 * satifying the conditions below.
> +	 * - Pn is in the range of Pn_min and Pn_max
> +	 * - F is in the range of 1 and 255
> +	 * - FxP is within 25% of desired value.
> +	 *   Note: 25% is arbitrary value and may need some tweak.
> +	 */
> +	ret = drm_dp_dpcd_readb(aux, DP_EDP_PWMGEN_BIT_COUNT_CAP_MIN, &pn_min);
> +	if (ret != 1) {
> +		DRM_DEBUG_KMS("%s: Failed to read pwmgen bit count cap min: %d\n", aux->name, ret);
> +		return 0;
> +	}
> +	ret = drm_dp_dpcd_readb(aux, DP_EDP_PWMGEN_BIT_COUNT_CAP_MAX, &pn_max);
> +	if (ret != 1) {
> +		DRM_DEBUG_KMS("%s: Failed to read pwmgen bit count cap max: %d\n", aux->name, ret);
> +		return 0;
> +	}
> +	pn_min &= DP_EDP_PWMGEN_BIT_COUNT_MASK;
> +	pn_max &= DP_EDP_PWMGEN_BIT_COUNT_MASK;
> +
> +	/* Ensure frequency is within 25% of desired value */
> +	fxp_min = DIV_ROUND_CLOSEST(fxp * 3, 4);
> +	fxp_max = DIV_ROUND_CLOSEST(fxp * 5, 4);
> +	if (fxp_min < (1 << pn_min) || (255 << pn_max) < fxp_max) {
> +		DRM_DEBUG_KMS("%s: Driver defined backlight frequency (%d) out of range\n",
> +			      aux->name, driver_pwm_freq_hz);
> +		return 0;
> +	}
> +
> +	for (pn = pn_max; pn >= pn_min; pn--) {
> +		f = clamp(DIV_ROUND_CLOSEST(fxp, 1 << pn), 1, 255);
> +		fxp_actual = f << pn;
> +		if (fxp_min <= fxp_actual && fxp_actual <= fxp_max)
> +			break;
> +	}
> +
> +	ret = drm_dp_dpcd_writeb(aux, DP_EDP_PWMGEN_BIT_COUNT, pn);
> +	if (ret != 1) {
> +		DRM_DEBUG_KMS("%s: Failed to write aux pwmgen bit count: %d\n", aux->name, ret);
> +		return 0;
> +	}
> +	bl->pwmgen_bit_count = pn;
> +	bl->max = (1 << pn) - 1;
> +
> +	if (edp_dpcd[2] & DP_EDP_BACKLIGHT_FREQ_AUX_SET_CAP) {
> +		bl->pwm_freq_pre_divider = f;
> +		DRM_DEBUG_KMS("%s: Using backlight frequency from driver (%dHz)\n",
> +			      aux->name, driver_pwm_freq_hz);
> +	}
> +
> +	return 0;
> +}
> +
> +static inline int
> +drm_edp_backlight_probe_level(struct drm_dp_aux *aux, struct drm_edp_backlight_info *bl,
> +			      u8 *current_mode)
> +{
> +	int ret;
> +	u8 buf[2];
> +	u8 mode_reg;
> +
> +	ret = drm_dp_dpcd_readb(aux, DP_EDP_BACKLIGHT_MODE_SET_REGISTER, &mode_reg);
> +	if (ret != 1) {
> +		DRM_DEBUG_KMS("%s: Failed to read backlight mode: %d\n", aux->name, ret);
> +		return ret < 0 ? ret : -EIO;
> +	}
> +
> +	*current_mode = (mode_reg & DP_EDP_BACKLIGHT_CONTROL_MODE_MASK);
> +	if (*current_mode == DP_EDP_BACKLIGHT_CONTROL_MODE_DPCD) {
> +		int size = 1 + bl->lsb_reg_used;
> +
> +		ret = drm_dp_dpcd_read(aux, DP_EDP_BACKLIGHT_BRIGHTNESS_MSB, buf, size);
> +		if (ret != size) {
> +			DRM_DEBUG_KMS("%s: Failed to read backlight level: %d\n", aux->name, ret);
> +			return ret < 0 ? ret : -EIO;
> +		}
> +
> +		if (bl->lsb_reg_used)
> +			return (buf[0] << 8) | buf[1];
> +		else
> +			return buf[0];
> +	}
> +
> +	/*
> +	 * If we're not in DPCD control mode yet, the programmed brightness value is meaningless and
> +	 * the driver should assume max brightness
> +	 */
> +	return bl->max;
> +}
> +
> +/**
> + * drm_edp_backlight_init() - Probe a display panel's TCON using the standard VESA eDP backlight
> + * interface.
> + * @aux: The DP aux device to use for probing
> + * @bl: The &drm_edp_backlight_info struct to fill out with information on the backlight
> + * @driver_pwm_freq_hz: Optional PWM frequency from the driver in hz
> + * @edp_dpcd: A cached copy of the eDP DPCD
> + * @current_level: Where to store the probed brightness level
> + * @current_mode: Where to store the currently set backlight control mode
> + *
> + * Initializes a &drm_edp_backlight_info struct by probing @aux for it's backlight capabilities,
> + * along with also probing the current and maximum supported brightness levels.
> + *
> + * If @driver_pwm_freq_hz is non-zero, this will be used as the backlight frequency. Otherwise, the
> + * default frequency from the panel is used.
> + *
> + * Returns: %0 on success, negative error code on failure.
> + */
> +int
> +drm_edp_backlight_init(struct drm_dp_aux *aux, struct drm_edp_backlight_info *bl,
> +		       u16 driver_pwm_freq_hz, const u8 edp_dpcd[EDP_DISPLAY_CTL_CAP_SIZE],
> +		       u16 *current_level, u8 *current_mode)
> +{
> +	int ret;
> +
> +	if (edp_dpcd[1] & DP_EDP_BACKLIGHT_AUX_ENABLE_CAP)
> +		bl->aux_enable = true;
> +	if (edp_dpcd[2] & DP_EDP_BACKLIGHT_BRIGHTNESS_BYTE_COUNT)
> +		bl->lsb_reg_used = true;
> +
> +	ret = drm_edp_backlight_probe_max(aux, bl, driver_pwm_freq_hz, edp_dpcd);
> +	if (ret < 0)
> +		return ret;
> +
> +	ret = drm_edp_backlight_probe_level(aux, bl, current_mode);
> +	if (ret < 0)
> +		return ret;
> +	*current_level = ret;
> +
> +	DRM_DEBUG_KMS("%s: Found backlight level=%d/%d pwm_freq_pre_divider=%d mode=%x\n",
> +		      aux->name, *current_level, bl->max, bl->pwm_freq_pre_divider, *current_mode);
> +	DRM_DEBUG_KMS("%s: Backlight caps: pwmgen_bit_count=%d lsb_reg_used=%d aux_enable=%d\n",
> +		      aux->name, bl->pwmgen_bit_count, bl->lsb_reg_used, bl->aux_enable);
> +	return 0;
> +}
> +EXPORT_SYMBOL(drm_edp_backlight_init);
> diff --git a/drivers/gpu/drm/i915/display/intel_display_types.h b/drivers/gpu/drm/i915/display/intel_display_types.h
> index 8450ab8fb245..2af208f1b467 100644
> --- a/drivers/gpu/drm/i915/display/intel_display_types.h
> +++ b/drivers/gpu/drm/i915/display/intel_display_types.h
> @@ -263,8 +263,7 @@ struct intel_panel {
>  		/* DPCD backlight */
>  		union {
>  			struct {
> -				u8 pwmgen_bit_count;
> -				u8 pwm_freq_pre_divider;
> +				struct drm_edp_backlight_info info;
>  			} vesa;
>  			struct {
>  				bool sdr_uses_aux;
> diff --git a/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c b/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c
> index 62294967f430..1ae14bc9e3fe 100644
> --- a/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c
> +++ b/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c
> @@ -268,109 +268,19 @@ intel_dp_aux_hdr_setup_backlight(struct intel_connector *connector, enum pipe pi
>  }
>  
>  /* VESA backlight callbacks */
> -static void set_vesa_backlight_enable(struct intel_dp *intel_dp, bool enable)
> -{
> -	struct drm_i915_private *i915 = dp_to_i915(intel_dp);
> -	u8 reg_val = 0;
> -
> -	/* Early return when display use other mechanism to enable backlight. */
> -	if (!(intel_dp->edp_dpcd[1] & DP_EDP_BACKLIGHT_AUX_ENABLE_CAP))
> -		return;
> -
> -	if (drm_dp_dpcd_readb(&intel_dp->aux, DP_EDP_DISPLAY_CONTROL_REGISTER,
> -			      &reg_val) < 0) {
> -		drm_dbg_kms(&i915->drm, "Failed to read DPCD register 0x%x\n",
> -			    DP_EDP_DISPLAY_CONTROL_REGISTER);
> -		return;
> -	}
> -	if (enable)
> -		reg_val |= DP_EDP_BACKLIGHT_ENABLE;
> -	else
> -		reg_val &= ~(DP_EDP_BACKLIGHT_ENABLE);
> -
> -	if (drm_dp_dpcd_writeb(&intel_dp->aux, DP_EDP_DISPLAY_CONTROL_REGISTER,
> -			       reg_val) != 1) {
> -		drm_dbg_kms(&i915->drm, "Failed to %s aux backlight\n",
> -			    enable ? "enable" : "disable");
> -	}
> -}
> -
> -static bool intel_dp_aux_vesa_backlight_dpcd_mode(struct intel_connector *connector)
> -{
> -	struct intel_dp *intel_dp = intel_attached_dp(connector);
> -	struct drm_i915_private *i915 = dp_to_i915(intel_dp);
> -	u8 mode_reg;
> -
> -	if (drm_dp_dpcd_readb(&intel_dp->aux,
> -			      DP_EDP_BACKLIGHT_MODE_SET_REGISTER,
> -			      &mode_reg) != 1) {
> -		drm_dbg_kms(&i915->drm,
> -			    "Failed to read the DPCD register 0x%x\n",
> -			    DP_EDP_BACKLIGHT_MODE_SET_REGISTER);
> -		return false;
> -	}
> -
> -	return (mode_reg & DP_EDP_BACKLIGHT_CONTROL_MODE_MASK) ==
> -	       DP_EDP_BACKLIGHT_CONTROL_MODE_DPCD;
> -}
> -
> -/*
> - * Read the current backlight value from DPCD register(s) based
> - * on if 8-bit(MSB) or 16-bit(MSB and LSB) values are supported
> - */
>  static u32 intel_dp_aux_vesa_get_backlight(struct intel_connector *connector, enum pipe unused)
>  {
> -	struct intel_dp *intel_dp = intel_attached_dp(connector);
> -	struct drm_i915_private *i915 = dp_to_i915(intel_dp);
> -	u8 read_val[2] = { 0x0 };
> -	u16 level = 0;
> -
> -	/*
> -	 * If we're not in DPCD control mode yet, the programmed brightness
> -	 * value is meaningless and we should assume max brightness
> -	 */
> -	if (!intel_dp_aux_vesa_backlight_dpcd_mode(connector))
> -		return connector->panel.backlight.max;
> -
> -	if (drm_dp_dpcd_read(&intel_dp->aux, DP_EDP_BACKLIGHT_BRIGHTNESS_MSB,
> -			     &read_val, sizeof(read_val)) < 0) {
> -		drm_dbg_kms(&i915->drm, "Failed to read DPCD register 0x%x\n",
> -			    DP_EDP_BACKLIGHT_BRIGHTNESS_MSB);
> -		return 0;
> -	}
> -	level = read_val[0];
> -	if (intel_dp->edp_dpcd[2] & DP_EDP_BACKLIGHT_BRIGHTNESS_BYTE_COUNT)
> -		level = (read_val[0] << 8 | read_val[1]);
> -
> -	return level;
> +	return connector->panel.backlight.level;
>  }
>  
> -/*
> - * Sends the current backlight level over the aux channel, checking if its using
> - * 8-bit or 16 bit value (MSB and LSB)
> - */
>  static void
> -intel_dp_aux_vesa_set_backlight(const struct drm_connector_state *conn_state,
> -				u32 level)
> +intel_dp_aux_vesa_set_backlight(const struct drm_connector_state *conn_state, u32 level)
>  {
>  	struct intel_connector *connector = to_intel_connector(conn_state->connector);
> -	struct intel_dp *intel_dp = intel_attached_dp(connector);
> -	struct drm_i915_private *i915 = dp_to_i915(intel_dp);
> -	u8 vals[2] = { 0x0 };
> -
> -	vals[0] = level;
> +	struct intel_panel *panel = &connector->panel;
> +	struct intel_dp *intel_dp = enc_to_intel_dp(connector->encoder);
>  
> -	/* Write the MSB and/or LSB */
> -	if (intel_dp->edp_dpcd[2] & DP_EDP_BACKLIGHT_BRIGHTNESS_BYTE_COUNT) {
> -		vals[0] = (level & 0xFF00) >> 8;
> -		vals[1] = (level & 0xFF);
> -	}
> -	if (drm_dp_dpcd_write(&intel_dp->aux, DP_EDP_BACKLIGHT_BRIGHTNESS_MSB,
> -			      vals, sizeof(vals)) < 0) {
> -		drm_dbg_kms(&i915->drm,
> -			    "Failed to write aux backlight level\n");
> -		return;
> -	}
> +	drm_edp_backlight_set_level(&intel_dp->aux, &panel->backlight.edp.vesa.info, level);
>  }
>  
>  static void
> @@ -378,176 +288,46 @@ intel_dp_aux_vesa_enable_backlight(const struct intel_crtc_state *crtc_state,
>  				   const struct drm_connector_state *conn_state, u32 level)
>  {
>  	struct intel_connector *connector = to_intel_connector(conn_state->connector);
> -	struct intel_dp *intel_dp = intel_attached_dp(connector);
> -	struct drm_i915_private *i915 = dp_to_i915(intel_dp);
>  	struct intel_panel *panel = &connector->panel;
> -	u8 dpcd_buf, new_dpcd_buf, edp_backlight_mode;
> -	u8 pwmgen_bit_count = panel->backlight.edp.vesa.pwmgen_bit_count;
> -
> -	if (drm_dp_dpcd_readb(&intel_dp->aux,
> -			DP_EDP_BACKLIGHT_MODE_SET_REGISTER, &dpcd_buf) != 1) {
> -		drm_dbg_kms(&i915->drm, "Failed to read DPCD register 0x%x\n",
> -			    DP_EDP_BACKLIGHT_MODE_SET_REGISTER);
> -		return;
> -	}
> -
> -	new_dpcd_buf = dpcd_buf;
> -	edp_backlight_mode = dpcd_buf & DP_EDP_BACKLIGHT_CONTROL_MODE_MASK;
> -
> -	switch (edp_backlight_mode) {
> -	case DP_EDP_BACKLIGHT_CONTROL_MODE_PWM:
> -	case DP_EDP_BACKLIGHT_CONTROL_MODE_PRESET:
> -	case DP_EDP_BACKLIGHT_CONTROL_MODE_PRODUCT:
> -		new_dpcd_buf &= ~DP_EDP_BACKLIGHT_CONTROL_MODE_MASK;
> -		new_dpcd_buf |= DP_EDP_BACKLIGHT_CONTROL_MODE_DPCD;
> -
> -		if (drm_dp_dpcd_writeb(&intel_dp->aux,
> -				       DP_EDP_PWMGEN_BIT_COUNT,
> -				       pwmgen_bit_count) < 0)
> -			drm_dbg_kms(&i915->drm,
> -				    "Failed to write aux pwmgen bit count\n");
> -
> -		break;
> -
> -	/* Do nothing when it is already DPCD mode */
> -	case DP_EDP_BACKLIGHT_CONTROL_MODE_DPCD:
> -	default:
> -		break;
> -	}
> -
> -	if (panel->backlight.edp.vesa.pwm_freq_pre_divider) {
> -		if (drm_dp_dpcd_writeb(&intel_dp->aux, DP_EDP_BACKLIGHT_FREQ_SET,
> -				       panel->backlight.edp.vesa.pwm_freq_pre_divider) == 1)
> -			new_dpcd_buf |= DP_EDP_BACKLIGHT_FREQ_AUX_SET_ENABLE;
> -		else
> -			drm_dbg_kms(&i915->drm, "Failed to write aux backlight frequency\n");
> -	}
> -
> -	if (new_dpcd_buf != dpcd_buf) {
> -		if (drm_dp_dpcd_writeb(&intel_dp->aux,
> -			DP_EDP_BACKLIGHT_MODE_SET_REGISTER, new_dpcd_buf) < 0) {
> -			drm_dbg_kms(&i915->drm,
> -				    "Failed to write aux backlight mode\n");
> -		}
> -	}
> +	struct intel_dp *intel_dp = enc_to_intel_dp(connector->encoder);
>  
> -	intel_dp_aux_vesa_set_backlight(conn_state, level);
> -	set_vesa_backlight_enable(intel_dp, true);
> +	drm_edp_backlight_enable(&intel_dp->aux, &panel->backlight.edp.vesa.info, level);
>  }
>  
>  static void intel_dp_aux_vesa_disable_backlight(const struct drm_connector_state *old_conn_state,
>  						u32 level)
>  {
> -	set_vesa_backlight_enable(enc_to_intel_dp(to_intel_encoder(old_conn_state->best_encoder)),
> -				  false);
> -}
> -
> -/*
> - * Compute PWM frequency divider value based off the frequency provided to us by the vbt.
> - * The PWM Frequency is calculated as 27Mhz / (F x P).
> - * - Where F = PWM Frequency Pre-Divider value programmed by field 7:0 of the
> - *             EDP_BACKLIGHT_FREQ_SET register (DPCD Address 00728h)
> - * - Where P = 2^Pn, where Pn is the value programmed by field 4:0 of the
> - *             EDP_PWMGEN_BIT_COUNT register (DPCD Address 00724h)
> - */
> -static u32 intel_dp_aux_vesa_calc_max_backlight(struct intel_connector *connector)
> -{
> -	struct drm_i915_private *i915 = to_i915(connector->base.dev);
> -	struct intel_dp *intel_dp = intel_attached_dp(connector);
> +	struct intel_connector *connector = to_intel_connector(old_conn_state->connector);
>  	struct intel_panel *panel = &connector->panel;
> -	u32 max_backlight = 0;
> -	int freq, fxp, fxp_min, fxp_max, fxp_actual, f = 1;
> -	u8 pn, pn_min, pn_max;
> -
> -	if (drm_dp_dpcd_readb(&intel_dp->aux, DP_EDP_PWMGEN_BIT_COUNT, &pn) == 1) {
> -		pn &= DP_EDP_PWMGEN_BIT_COUNT_MASK;
> -		max_backlight = (1 << pn) - 1;
> -	}
> -
> -	/* Find desired value of (F x P)
> -	 * Note that, if F x P is out of supported range, the maximum value or
> -	 * minimum value will applied automatically. So no need to check that.
> -	 */
> -	freq = i915->vbt.backlight.pwm_freq_hz;
> -	drm_dbg_kms(&i915->drm, "VBT defined backlight frequency %u Hz\n",
> -		    freq);
> -	if (!freq) {
> -		drm_dbg_kms(&i915->drm,
> -			    "Use panel default backlight frequency\n");
> -		return max_backlight;
> -	}
> -
> -	fxp = DIV_ROUND_CLOSEST(KHz(DP_EDP_BACKLIGHT_FREQ_BASE_KHZ), freq);
> -
> -	/* Use highest possible value of Pn for more granularity of brightness
> -	 * adjustment while satifying the conditions below.
> -	 * - Pn is in the range of Pn_min and Pn_max
> -	 * - F is in the range of 1 and 255
> -	 * - FxP is within 25% of desired value.
> -	 *   Note: 25% is arbitrary value and may need some tweak.
> -	 */
> -	if (drm_dp_dpcd_readb(&intel_dp->aux,
> -			      DP_EDP_PWMGEN_BIT_COUNT_CAP_MIN, &pn_min) != 1) {
> -		drm_dbg_kms(&i915->drm,
> -			    "Failed to read pwmgen bit count cap min\n");
> -		return max_backlight;
> -	}
> -	if (drm_dp_dpcd_readb(&intel_dp->aux,
> -			      DP_EDP_PWMGEN_BIT_COUNT_CAP_MAX, &pn_max) != 1) {
> -		drm_dbg_kms(&i915->drm,
> -			    "Failed to read pwmgen bit count cap max\n");
> -		return max_backlight;
> -	}
> -	pn_min &= DP_EDP_PWMGEN_BIT_COUNT_MASK;
> -	pn_max &= DP_EDP_PWMGEN_BIT_COUNT_MASK;
> -
> -	/* Ensure frequency is within 25% of desired value */
> -	fxp_min = DIV_ROUND_CLOSEST(fxp * 3, 4);
> -	fxp_max = DIV_ROUND_CLOSEST(fxp * 5, 4);
> -
> -	if (fxp_min < (1 << pn_min) || (255 << pn_max) < fxp_max) {
> -		drm_dbg_kms(&i915->drm,
> -			    "VBT defined backlight frequency out of range\n");
> -		return max_backlight;
> -	}
> -
> -	for (pn = pn_max; pn >= pn_min; pn--) {
> -		f = clamp(DIV_ROUND_CLOSEST(fxp, 1 << pn), 1, 255);
> -		fxp_actual = f << pn;
> -		if (fxp_min <= fxp_actual && fxp_actual <= fxp_max)
> -			break;
> -	}
> -
> -	drm_dbg_kms(&i915->drm, "Using eDP pwmgen bit count of %d\n", pn);
> -	if (drm_dp_dpcd_writeb(&intel_dp->aux,
> -			       DP_EDP_PWMGEN_BIT_COUNT, pn) < 0) {
> -		drm_dbg_kms(&i915->drm,
> -			    "Failed to write aux pwmgen bit count\n");
> -		return max_backlight;
> -	}
> -
> -	panel->backlight.edp.vesa.pwmgen_bit_count = pn;
> -	if (intel_dp->edp_dpcd[2] & DP_EDP_BACKLIGHT_FREQ_AUX_SET_CAP)
> -		panel->backlight.edp.vesa.pwm_freq_pre_divider = f;
> -
> -	max_backlight = (1 << pn) - 1;
> +	struct intel_dp *intel_dp = enc_to_intel_dp(connector->encoder);
>  
> -	return max_backlight;
> +	drm_edp_backlight_disable(&intel_dp->aux, &panel->backlight.edp.vesa.info);
>  }
>  
> -static int intel_dp_aux_vesa_setup_backlight(struct intel_connector *connector,
> -					     enum pipe pipe)
> +static int intel_dp_aux_vesa_setup_backlight(struct intel_connector *connector, enum pipe pipe)
>  {
>  	struct intel_panel *panel = &connector->panel;
> +	struct intel_dp *intel_dp = enc_to_intel_dp(connector->encoder);
> +	struct drm_i915_private *i915 = dp_to_i915(intel_dp);
> +	u16 current_level;
> +	u8 current_mode;
> +	int ret;
>  
> -	panel->backlight.max = intel_dp_aux_vesa_calc_max_backlight(connector);
> -	if (!panel->backlight.max)
> -		return -ENODEV;
> +	ret = drm_edp_backlight_init(&intel_dp->aux, &panel->backlight.edp.vesa.info,
> +				     i915->vbt.backlight.pwm_freq_hz, intel_dp->edp_dpcd,
> +				     &current_level, &current_mode);
> +	if (ret < 0)
> +		return ret;
>  
> +	panel->backlight.max = panel->backlight.edp.vesa.info.max;
>  	panel->backlight.min = 0;
> -	panel->backlight.level = intel_dp_aux_vesa_get_backlight(connector, pipe);
> -	panel->backlight.enabled = intel_dp_aux_vesa_backlight_dpcd_mode(connector) &&
> -				   panel->backlight.level != 0;
> +	if (current_mode == DP_EDP_BACKLIGHT_CONTROL_MODE_DPCD) {
> +		panel->backlight.level = current_level;
> +		panel->backlight.enabled = panel->backlight.level != 0;
> +	} else {
> +		panel->backlight.level = panel->backlight.max;
> +		panel->backlight.enabled = false;
> +	}
>  
>  	return 0;
>  }
> @@ -558,16 +338,12 @@ intel_dp_aux_supports_vesa_backlight(struct intel_connector *connector)
>  	struct intel_dp *intel_dp = intel_attached_dp(connector);
>  	struct drm_i915_private *i915 = dp_to_i915(intel_dp);
>  
> -	/* Check the eDP Display control capabilities registers to determine if
> -	 * the panel can support backlight control over the aux channel.
> -	 *
> -	 * TODO: We currently only support AUX only backlight configurations, not backlights which
> +	/* TODO: We currently only support AUX only backlight configurations, not backlights which
>  	 * require a mix of PWM and AUX controls to work. In the mean time, these machines typically
>  	 * work just fine using normal PWM controls anyway.
>  	 */
> -	if (intel_dp->edp_dpcd[1] & DP_EDP_TCON_BACKLIGHT_ADJUSTMENT_CAP &&
> -	    (intel_dp->edp_dpcd[1] & DP_EDP_BACKLIGHT_AUX_ENABLE_CAP) &&
> -	    (intel_dp->edp_dpcd[2] & DP_EDP_BACKLIGHT_BRIGHTNESS_AUX_SET_CAP)) {
> +	if ((intel_dp->edp_dpcd[1] & DP_EDP_BACKLIGHT_AUX_ENABLE_CAP) &&
> +	    drm_edp_backlight_supported(intel_dp->edp_dpcd)) {
>  		drm_dbg_kms(&i915->drm, "AUX Backlight Control Supported!\n");
>  		return true;
>  	}
> diff --git a/include/drm/drm_dp_helper.h b/include/drm/drm_dp_helper.h
> index edffd1dcca3e..1eca0b42fc45 100644
> --- a/include/drm/drm_dp_helper.h
> +++ b/include/drm/drm_dp_helper.h
> @@ -1790,6 +1790,24 @@ drm_dp_sink_can_do_video_without_timing_msa(const u8 dpcd[DP_RECEIVER_CAP_SIZE])
>  		DP_MSA_TIMING_PAR_IGNORED;
>  }
>  
> +/**
> + * drm_edp_backlight_supported() - Check an eDP DPCD for VESA backlight support
> + * @edp_dpcd: The DPCD to check
> + *
> + * Note that currently this function will return %false for panels which support various DPCD
> + * backlight features but which require the brightness be set through PWM, and don't support setting
> + * the brightness level via the DPCD. This is a TODO.
> + *
> + * Returns: %True if @edp_dpcd indicates that VESA backlight controls are supported, %false
> + * otherwise
> + */
> +static inline bool
> +drm_edp_backlight_supported(const u8 edp_dpcd[EDP_DISPLAY_CTL_CAP_SIZE])
> +{
> +	return (edp_dpcd[1] & DP_EDP_TCON_BACKLIGHT_ADJUSTMENT_CAP) &&
> +		(edp_dpcd[2] & DP_EDP_BACKLIGHT_BRIGHTNESS_AUX_SET_CAP);
> +}
> +
>  /*
>   * DisplayPort AUX channel
>   */
> @@ -2089,6 +2107,36 @@ drm_dp_has_quirk(const struct drm_dp_desc *desc, enum drm_dp_quirk quirk)
>  	return desc->quirks & BIT(quirk);
>  }
>  
> +/**
> + * struct drm_edp_backlight_info - Probed eDP backlight info struct
> + * @pwmgen_bit_count: The pwmgen bit count
> + * @pwm_freq_pre_divider: The PWM frequency pre-divider value being used for this backlight, if any
> + * @max: The maximum backlight level that may be set
> + * @lsb_reg_used: Do we also write values to the DP_EDP_BACKLIGHT_BRIGHTNESS_LSB register?
> + * @aux_enable: Does the panel support the AUX enable cap?
> + *
> + * This structure contains various data about an eDP backlight, which can be populated by using
> + * drm_edp_backlight_init().
> + */
> +struct drm_edp_backlight_info {
> +	u8 pwmgen_bit_count;
> +	u8 pwm_freq_pre_divider;
> +	u16 max;
> +
> +	bool lsb_reg_used : 1;
> +	bool aux_enable : 1;
> +};
> +
> +int
> +drm_edp_backlight_init(struct drm_dp_aux *aux, struct drm_edp_backlight_info *bl,
> +		       u16 driver_pwm_freq_hz, const u8 edp_dpcd[EDP_DISPLAY_CTL_CAP_SIZE],
> +		       u16 *current_level, u8 *current_mode);
> +int drm_edp_backlight_set_level(struct drm_dp_aux *aux, const struct drm_edp_backlight_info *bl,
> +				u16 level);
> +int drm_edp_backlight_enable(struct drm_dp_aux *aux, const struct drm_edp_backlight_info *bl,
> +			     u16 level);
> +int drm_edp_backlight_disable(struct drm_dp_aux *aux, const struct drm_edp_backlight_info *bl);
> +
>  #ifdef CONFIG_DRM_DP_CEC
>  void drm_dp_cec_irq(struct drm_dp_aux *aux);
>  void drm_dp_cec_register_connector(struct drm_dp_aux *aux,
> -- 
> 2.29.2
> 
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