[Intel-gfx] [PATCH] drm/i915: Readout conn_state->max_bpc

[Chris Wilson]

Quoting Ville Syrjala (2021-02-16 16:00:35)
> From: Ville Syrjälä <ville.syrjala at linux.intel.com>
> 
> Populate conn_state->max_bpc with something sensible from the start.
> Otherwise it's possible that we get to compute_sink_pipe_bpp() with
> max_bpc==0.
> 
> The specific scenario goes as follows:
> 1. Initial connector state allocated with max_bpc==0
> 2. Trigger a modeset on the crtc feeding the connector, without
>    actually adding the connector to the commit
> 3. drm_atomic_connector_check() is skipped because the
>    connector has not yet been added, hence conn_state->max_bpc
>    retains its current value
> 4. drm_atomic_helper_check_modeset() ->
>    drm_atomic_add_affected_connectors() -> the connector
>    is now part of the commit
> 5. compute_baseline_pipe_bpp() -> MISSING_CASE(max_bpc==0)
> 
> Note that pipe_bpp itself may not be populated on pre-g4x machines,
> in which case we just fall back to max_bpc==8 and let .compute_config()
> limit the resulting pipe_bpp further if necessary.
> 
> Cc: Daniel Vetter <daniel at ffwll.ch>
> Reported-by: Chris Wilson <chris at chris-wilson.co.uk>
> Signed-off-by: Ville Syrjälä <ville.syrjala at linux.intel.com>
Tested-by: Chris Wilson <chris at chris-wilson.co.uk>
-Chris