Re: [PATCH] drm/i915: Unset legacy_cursor_update early in intel_atomic_commit, v2.

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Op 18-09-17 om 17:03 schreef Ville Syrjälä:
> On Mon, Sep 18, 2017 at 12:12:50PM +0200, Maarten Lankhorst wrote:
>> Commit b44d5c0c105a ("drm/i915: Always wait for flip_done, v2.") removed
>> the call to wait_for_vblanks and replaced it with flip_done.
>>
>> Unfortunately legacy_cursor_update was unset too late, and the
>> replacement call drm_atomic_helper_wait_for_flip_done() was
>> a noop. Make sure that its unset before setup_commit() is
>> called to fix this issue.
>>
>> Changes since v1:
>> - Force vblank wait for watermarks not yet converted to atomic too. (Ville)
>> - Use for_each_new_intel_crtc_in_state. (Ville)
>>
>> Signed-off-by: Maarten Lankhorst <maarten.lankhorst@xxxxxxxxxxxxxxx>
>> Fixes: b44d5c0c105a ("drm/i915: Always wait for flip_done, v2.")
>> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=102675
>> Testcase: kms_cursor_crc
>> Cc: Daniel Vetter <daniel.vetter@xxxxxxxx>
>> Cc: Jani Nikula <jani.nikula@xxxxxxxxxxxxxxx>
>> Reported-by: Marta Löfstedt <marta.lofstedt@xxxxxxxxx>
>> Cc: Marta Löfstedt <marta.lofstedt@xxxxxxxxx>
>> Tested-by: Marta Löfstedt <marta.lofstedt@xxxxxxxxx>
>> Cc: Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx>
>> ---
>>  drivers/gpu/drm/i915/intel_display.c | 45 +++++++++++++++++++++---------------
>>  1 file changed, 26 insertions(+), 19 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
>> index 8599e425abb1..8d051256da1e 100644
>> --- a/drivers/gpu/drm/i915/intel_display.c
>> +++ b/drivers/gpu/drm/i915/intel_display.c
>> @@ -12517,21 +12517,10 @@ static int intel_atomic_commit(struct drm_device *dev,
>>  	struct drm_i915_private *dev_priv = to_i915(dev);
>>  	int ret = 0;
>>  
>> -	ret = drm_atomic_helper_setup_commit(state, nonblock);
>> -	if (ret)
>> -		return ret;
>> -
>>  	drm_atomic_state_get(state);
>>  	i915_sw_fence_init(&intel_state->commit_ready,
>>  			   intel_atomic_commit_ready);
>>  
>> -	ret = intel_atomic_prepare_commit(dev, state);
>> -	if (ret) {
>> -		DRM_DEBUG_ATOMIC("Preparing state failed with %i\n", ret);
>> -		i915_sw_fence_commit(&intel_state->commit_ready);
>> -		return ret;
>> -	}
>> -
>>  	/*
>>  	 * The intel_legacy_cursor_update() fast path takes care
>>  	 * of avoiding the vblank waits for simple cursor
>> @@ -12540,19 +12529,37 @@ static int intel_atomic_commit(struct drm_device *dev,
>>  	 * updates happen during the correct frames. Gen9+ have
>>  	 * double buffered watermarks and so shouldn't need this.
>>  	 *
>> -	 * Do this after drm_atomic_helper_setup_commit() and
>> -	 * intel_atomic_prepare_commit() because we still want
>> -	 * to skip the flip and fb cleanup waits. Although that
>> -	 * does risk yanking the mapping from under the display
>> -	 * engine.
>> +	 * Unset state->legacy_cursor_update before the call to
>> +	 * drm_atomic_helper_setup_commit() because otherwise
>> +	 * drm_atomic_helper_wait_for_flip_done() is a noop and
>> +	 * we get FIFO underruns because we didn't wait
>> +	 * for vblank.
>>  	 *
>>  	 * FIXME doing watermarks and fb cleanup from a vblank worker
>>  	 * (assuming we had any) would solve these problems.
>>  	 */
>> -	if (INTEL_GEN(dev_priv) < 9)
>> -		state->legacy_cursor_update = false;
>> +	if (INTEL_GEN(dev_priv) < 9 && state->legacy_cursor_update) {
>> +		struct intel_crtc_state *new_crtc_state;
>> +		struct intel_crtc *crtc;
>> +		int i;
>> +
>> +		for_each_new_intel_crtc_in_state(intel_state, crtc, new_crtc_state, i)
>> +			if (new_crtc_state->wm.need_postvbl_update ||
>> +			    new_crtc_state->update_wm_post)
>> +				state->legacy_cursor_update = false;
> Hmm. I guess that's better. But I still don't see why you want to change
> this bit of code in this patch. AFAICS it's got nothing to do with the fix
> itself, and instead it's just trying to optimize some cursor updates
> that were kicked over to the slow path. Or am I missing something?

We accidentally removed the vblank wait for the slowpath, but I don't think we should reintroduce the vblank except where we need it..

~Maarten

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