Re: [PATCH v6 14/23] drm/modes: Properly generate a drm_display_mode from a named mode

[Noralf Trønnes]

Den 26.10.2022 17.33, skrev maxime@xxxxxxxxxx:
> The framework will get the drm_display_mode from the drm_cmdline_mode it
> got by parsing the video command line argument by calling
> drm_connector_pick_cmdline_mode().
> 
> The heavy lifting will then be done by the drm_mode_create_from_cmdline_mode()
> function.
> 
> In the case of the named modes though, there's no real code to make that
> translation and we rely on the drivers to guess which actual display mode
> we meant.
> 
> Let's modify drm_mode_create_from_cmdline_mode() to properly generate the
> drm_display_mode we mean when passing a named mode.
> 
> Signed-off-by: Maxime Ripard <maxime@xxxxxxxxxx>
> 
> ---
> Changes in v6:
> - Fix get_modes to return 0 instead of an error code
> - Rename the tests to follow the DRM test naming convention
> 
> Changes in v5:
> - Switched to KUNIT_ASSERT_NOT_NULL
> ---
>  drivers/gpu/drm/drm_modes.c                     | 34 ++++++++++-
>  drivers/gpu/drm/tests/drm_client_modeset_test.c | 77 ++++++++++++++++++++++++-
>  2 files changed, 109 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_modes.c b/drivers/gpu/drm/drm_modes.c
> index dc037f7ceb37..85aa9898c229 100644
> --- a/drivers/gpu/drm/drm_modes.c
> +++ b/drivers/gpu/drm/drm_modes.c
> @@ -2497,6 +2497,36 @@ bool drm_mode_parse_command_line_for_connector(const char *mode_option,
>  }
>  EXPORT_SYMBOL(drm_mode_parse_command_line_for_connector);
>  
> +static struct drm_display_mode *drm_named_mode(struct drm_device *dev,
> +					       struct drm_cmdline_mode *cmd)
> +{
> +	struct drm_display_mode *mode;
> +	unsigned int i;
> +
> +	for (i = 0; i < ARRAY_SIZE(drm_named_modes); i++) {
> +		const struct drm_named_mode *named_mode = &drm_named_modes[i];
> +
> +		if (strcmp(cmd->name, named_mode->name))
> +			continue;
> +
> +		if (!named_mode->tv_mode)
> +			continue;
> +
> +		mode = drm_analog_tv_mode(dev,
> +					  named_mode->tv_mode,
> +					  named_mode->pixel_clock_khz * 1000,
> +					  named_mode->xres,
> +					  named_mode->yres,
> +					  named_mode->flags & DRM_MODE_FLAG_INTERLACE);
> +		if (!mode)
> +			return NULL;
> +
> +		return mode;
> +	}
> +
> +	return NULL;
> +}
> +
>  /**
>   * drm_mode_create_from_cmdline_mode - convert a command line modeline into a DRM display mode
>   * @dev: DRM device to create the new mode for
> @@ -2514,7 +2544,9 @@ drm_mode_create_from_cmdline_mode(struct drm_device *dev,
>  	if (cmd->xres == 0 || cmd->yres == 0)
>  		return NULL;
>  
> -	if (cmd->cvt)
> +	if (strlen(cmd->name))
> +		mode = drm_named_mode(dev, cmd);

I'm trying to track how this generated mode fits into to it all and
AFAICS if the connector already supports a mode with the same xres/yres
as the named mode, the named mode will never be created because of the
check at the beginning of drm_helper_probe_add_cmdline_mode(). It will
just mark the existing mode with USERDEF and return.

If the connector doesn't already support a mode with such a resolution
it will be created, but should we do that? If the driver supported such
a mode it would certainly already have added it to the mode list,
wouldn't it? After all it's just 2 variants NTSC and PAL.

We have this in drm_client_modeset.c:drm_connector_pick_cmdline_mode():

	list_for_each_entry(mode, &connector->modes, head) {
		/* Check (optional) mode name first */
		if (!strcmp(mode->name, cmdline_mode->name))
			return mode;

Here it looks like the named mode thing is a way to choose a mode, not
to add one.

I couldn't find any documentation on how named modes is supposed to
work, have you seen any?

Noralf.

> +	else if (cmd->cvt)
>  		mode = drm_cvt_mode(dev,
>  				    cmd->xres, cmd->yres,
>  				    cmd->refresh_specified ? cmd->refresh : 60,