Re: [PATCH 01/20] drm/bridge: add dsi_lp11_notify mechanism

[Alexander Stein]

Hi Michael,

Am Montag, 6. Mai 2024, 15:34:30 CEST schrieb Michael Walle:
> Some bridges have very strict power-up reqirements. In this case, the
> Toshiba TC358775. The reset has to be deasserted while *both* the DSI
> clock and DSI data lanes are in LP-11 mode. After the reset is relased,
> the bridge needs the DSI clock to actually be able to process I2C
> access. This access will configure the DSI side of the bridge during
> which the DSI data lanes have to be in LP-11 mode.

Apparently this is an issue for a lot of DSI bridges. But enabling LP-11 for
a bridge is impossible with current documentation [1], which states "A DSI
host should keep the PHY powered down until the pre_enable operation is
called."
Additionally tc358767/tc9595 (DSI-DP bridge) needs LP-11 for AUX channel
access to even get EDID. This is a requirement before pre_enable would
even be possible.

So some changes to the current flow are needed. But I am not so sure
about LP-11 notification. IMHO a device request to the DSI host to
enable LP-11 seems more sensible.

Best regards,
Alexander

[1] https://www.kernel.org/doc/html/latest/gpu/drm-kms-helpers.html#mipi-dsi-bridge-operation

> After everything is
> configured the video stream can finally be enabled.
> 
> This means:
>  (1) The bridge has to be configured completely in .pre_enable() op
>      (with the clock turned on and data lanes in LP-11 mode, thus
>      .pre_enable_prev_first has to be set).
>  (2) The bridge will enable its output in the .enable() op
>  (3) There must be some mechanism before (1) where the bridge can
>      release its reset while the clock lane is still in LP-11 mode.
> 
> Unfortunately, (3) is crucial for a correct operation of the bridge.
> To satisfy this requriment, introduce a new callback .dsi_lp11_notify()
> which will be called by the DSI host driver.
> 
> Signed-off-by: Michael Walle <mwalle@xxxxxxxxxx>
> ---
>  drivers/gpu/drm/drm_bridge.c | 16 ++++++++++++++++
>  include/drm/drm_bridge.h     | 12 ++++++++++++
>  2 files changed, 28 insertions(+)
> 
> diff --git a/drivers/gpu/drm/drm_bridge.c b/drivers/gpu/drm/drm_bridge.c
> index 28abe9aa99ca..98cd6558aecb 100644
> --- a/drivers/gpu/drm/drm_bridge.c
> +++ b/drivers/gpu/drm/drm_bridge.c
> @@ -1339,6 +1339,22 @@ void drm_bridge_hpd_notify(struct drm_bridge *bridge,
>  }
>  EXPORT_SYMBOL_GPL(drm_bridge_hpd_notify);
>  
> +/**
> + * drm_bridge_dsi_lp11_notify - notify clock/data lanes LP-11 mode
> + * @bridge: bridge control structure
> + *
> + * DSI host drivers shall call this function while the clock and data lanes
> + * are still in LP-11 mode.
> + *
> + * This function shall be called in a context that can sleep.
> + */
> +void drm_bridge_dsi_lp11_notify(struct drm_bridge *bridge)
> +{
> +	if (bridge->funcs->dsi_lp11_notify)
> +		bridge->funcs->dsi_lp11_notify(bridge);
> +}
> +EXPORT_SYMBOL_GPL(drm_bridge_dsi_lp11_notify);
> +
>  #ifdef CONFIG_OF
>  /**
>   * of_drm_find_bridge - find the bridge corresponding to the device node in
> diff --git a/include/drm/drm_bridge.h b/include/drm/drm_bridge.h
> index 4baca0d9107b..4ef61274e0a8 100644
> --- a/include/drm/drm_bridge.h
> +++ b/include/drm/drm_bridge.h
> @@ -630,6 +630,17 @@ struct drm_bridge_funcs {
>  	 */
>  	void (*hpd_disable)(struct drm_bridge *bridge);
>  
> +	/**
> +	 * dsi_lp11_notify:
> +	 *
> +	 * Will be called by the DSI host driver while both the DSI clock
> +	 * lane as well as the DSI data lanes are in LP-11 mode. Some bridges
> +	 * need this state while releasing the reset, for example.
> +	 * Not all DSI host drivers will support this. Therefore, the DSI
> +	 * bridge driver must not rely on this op to be called.
> +	 */
> +	void (*dsi_lp11_notify)(struct drm_bridge *bridge);
> +
>  	/**
>  	 * @debugfs_init:
>  	 *
> @@ -898,6 +909,7 @@ void drm_bridge_hpd_enable(struct drm_bridge *bridge,
>  void drm_bridge_hpd_disable(struct drm_bridge *bridge);
>  void drm_bridge_hpd_notify(struct drm_bridge *bridge,
>  			   enum drm_connector_status status);
> +void drm_bridge_dsi_lp11_notify(struct drm_bridge *bridge);
>  
>  #ifdef CONFIG_DRM_PANEL_BRIDGE
>  bool drm_bridge_is_panel(const struct drm_bridge *bridge);
> 
> 


-- 
TQ-Systems GmbH | Mühlstraße 2, Gut Delling | 82229 Seefeld, Germany
Amtsgericht München, HRB 105018
Geschäftsführer: Detlef Schneider, Rüdiger Stahl, Stefan Schneider
http://www.tq-group.com/