[PATCH 04/12] drm/client: Add a FIXME around crtc->mode usage

[Dmitry Baryshkov]

On Thu, Apr 04, 2024 at 11:33:28PM +0300, Ville Syrjala wrote:
> From: Ville Syrjälä <ville.syrjala at linux.intel.com>
> 
> crtc->mode is legacy junk and shouldn't really be used with
> atomic drivers.
> 
> Most (all?) atomic drivers do end up still calling
> drm_atomic_helper_update_legacy_modeset_state() at some
> point, so crtc->mode does still get populated, and this
> does work for now. But eventually would be nice to eliminate
> all the legacy stuff from atomic drivers.
> 
> Switching to crtc->state->mode would require some bigger
> changes however, as we currently drop the crtc->mutex
> before we're done using the mode. So leave the junk in
> for now and just add a FIXME to remind us that this
> needs fixing.


What about using allocated duplicate modes to fill modes[] array? This
requires additional allocations, but it will solve most if not all modes
lifetime issues.

> 
> Signed-off-by: Ville Syrjälä <ville.syrjala at linux.intel.com>
> ---
>  drivers/gpu/drm/drm_client_modeset.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/drivers/gpu/drm/drm_client_modeset.c b/drivers/gpu/drm/drm_client_modeset.c
> index 2b7d0be04911..8ef03608b424 100644
> --- a/drivers/gpu/drm/drm_client_modeset.c
> +++ b/drivers/gpu/drm/drm_client_modeset.c
> @@ -699,6 +699,10 @@ static bool drm_client_firmware_config(struct drm_client_dev *client,
>  			 *
>  			 * This is crtc->mode and not crtc->state->mode for the
>  			 * fastboot check to work correctly.
> +			 *
> +			 * FIXME using legacy crtc->mode with atomic drivers
> +			 * is dodgy. Switch to crtc->state->mode, after taking
> +			 * care of the resulting locking/lifetime issues.
>  			 */
>  			DRM_DEBUG_KMS("looking for current mode on connector %s\n",
>  				      connector->name);
> -- 
> 2.43.2
> 

-- 
With best wishes
Dmitry