[Intel-gfx] [PATCH v1 2/3] drm/i915/dsc: force full modeset whenever DSC is enabled at probe

[Matt Roper]

On Thu, Feb 13, 2020 at 04:04:11PM +0200, Stanislav Lisovskiy wrote:
> From: Jani Nikula <jani.nikula at intel.com>
> 
> We lack full state readout of DSC config, which may lead to DSC enable
> using a config that's all zeros, failing spectacularly. Force full
> modeset and thus compute config at probe to get a sane state, until we
> implement DSC state readout. Any fastset that did appear to work with
> DSC at probe, worked by coincidence. [1] is an example of a change that
> triggered the issue on TGL DSI DSC.
> 
> [1] http://patchwork.freedesktop.org/patch/msgid/20200212150102.7600-1-ville.syrjala@linux.intel.com
> 
> Cc: Manasi Navare <manasi.d.navare at intel.com>
> Cc: Vandita Kulkarni <vandita.kulkarni at intel.com>
> Cc: Ville Syrjala <ville.syrjala at linux.intel.com>
> Cc: stable at vger.kernel.org
> Signed-off-by: Jani Nikula <jani.nikula at intel.com>

Should this be

Fixes: fbacb15ea814 ("drm/i915/dsc: add basic hardware state readout support")

since that's where we added the basic readout with a FIXME to add more
later?

I don't know the specifics of DSC and what state we need, but the
approach here seems reasonable.

Acked-by: Matt Roper <matthew.d.roper at intel.com>

> ---
>  drivers/gpu/drm/i915/display/intel_display.c | 18 ++++++++++++++++++
>  1 file changed, 18 insertions(+)
> 
> diff --git a/drivers/gpu/drm/i915/display/intel_display.c b/drivers/gpu/drm/i915/display/intel_display.c
> index 61ba1f2256a0..1e3f2cc27db8 100644
> --- a/drivers/gpu/drm/i915/display/intel_display.c
> +++ b/drivers/gpu/drm/i915/display/intel_display.c
> @@ -17828,6 +17828,24 @@ static int intel_initial_commit(struct drm_device *dev)
>  			 * have readout for pipe gamma enable.
>  			 */
>  			crtc_state->uapi.color_mgmt_changed = true;
> +
> +			/*
> +			 * FIXME hack to force full modeset when DSC is being
> +			 * used.
> +			 *
> +			 * As long as we do not have full state readout and
> +			 * config comparison of crtc_state->dsc, we have no way
> +			 * to ensure reliable fastset. Remove once we have
> +			 * readout for DSC.
> +			 */
> +			if (crtc_state->dsc.compression_enable) {
> +				ret = drm_atomic_add_affected_connectors(state,
> +									 &crtc->base);
> +				if (ret)
> +					goto out;
> +				crtc_state->uapi.mode_changed = true;
> +				drm_dbg_kms(dev, "Force full modeset for DSC\n");
> +			}
>  		}
>  	}
>  
> -- 
> 2.24.1.485.gad05a3d8e5
> 
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-- 
Matt Roper
Graphics Software Engineer
VTT-OSGC Platform Enablement
Intel Corporation
(916) 356-2795