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

From: Jani Nikula <jani.nikula@intel.com>
To: Matt Roper <matthew.d.roper@intel.com>,
	Stanislav Lisovskiy <stanislav.lisovskiy@intel.com>
Cc: intel-gfx@lists.freedesktop.org
Subject: Re: [Intel-gfx] [PATCH v1 2/3] drm/i915/dsc: force full modeset whenever DSC is enabled at probe
Date: Thu, 13 Feb 2020 23:03:29 +0200	[thread overview]
Message-ID: <87tv3uw672.fsf@intel.com> (raw)
In-Reply-To: <20200213205650.GJ2014153@mdroper-desk1.amr.corp.intel.com>

On Thu, 13 Feb 2020, Matt Roper <matthew.d.roper@intel.com> wrote:
> On Thu, Feb 13, 2020 at 04:04:11PM +0200, Stanislav Lisovskiy wrote:
>> From: Jani Nikula <jani.nikula@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@intel.com>
>> Cc: Vandita Kulkarni <vandita.kulkarni@intel.com>
>> Cc: Ville Syrjala <ville.syrjala@linux.intel.com>
>> Cc: stable@vger.kernel.org
>> Signed-off-by: Jani Nikula <jani.nikula@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?

That added some readout and checks, but the problem existed before them
too.

BR,
Jani.

>
> 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@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
>> 
>> _______________________________________________
>> Intel-gfx mailing list
>> Intel-gfx@lists.freedesktop.org
>> https://lists.freedesktop.org/mailman/listinfo/intel-gfx

-- 
Jani Nikula, Intel Open Source Graphics Center
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