Re: [PATCH v3 03/12] drm/i915/display: Use async flip when available for initial plane config

[Maarten Lankhorst <maarten.lankhorst@linux.intel.com>]

Hello,

Den 2024-10-03 kl. 18:14, skrev Ville Syrjälä:
> On Thu, Oct 03, 2024 at 05:44:12PM +0200, Maarten Lankhorst wrote:
>> I'm planning to reorder readout in the Xe sequence in such a way that
>> interrupts will not be available, so just use an async flip.
>>
>> Since the new FB points to the same pages, it will not tear. It also
>> has the benefit of perhaps being slightly faster.
>>
>> Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
>> ---
>>   drivers/gpu/drm/i915/display/skl_universal_plane.c | 13 +++++++++++--
>>   1 file changed, 11 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/i915/display/skl_universal_plane.c b/drivers/gpu/drm/i915/display/skl_universal_plane.c
>> index fdb141cfa4274..73a3624e34098 100644
>> --- a/drivers/gpu/drm/i915/display/skl_universal_plane.c
>> +++ b/drivers/gpu/drm/i915/display/skl_universal_plane.c
>> @@ -2800,7 +2800,7 @@ bool skl_fixup_initial_plane_config(struct intel_crtc *crtc,
>>   		to_intel_plane_state(plane->base.state);
>>   	enum plane_id plane_id = plane->id;
>>   	enum pipe pipe = crtc->pipe;
>> -	u32 base;
>> +	u32 base, plane_ctl;
>>   
>>   	if (!plane_state->uapi.visible)
>>   		return false;
>> @@ -2814,7 +2814,16 @@ bool skl_fixup_initial_plane_config(struct intel_crtc *crtc,
>>   	if (plane_config->base == base)
>>   		return false;
>>   
>> +	/* Perform an async flip to the new surface. */
>> +	plane_ctl = intel_read(i915, PLANE_CTL(pipe, plane_id));
>> +	plane_ctl |= PLANE_CTL_ASYNC_FLIP;
>> +
> 
> No async flips!

Can you please explain your reasoning? I think async flip would fit 
perfectly here. We cannot perform a wait_for_vblank as we will not have 
interrupts enabled yet. Additionally an async flip would cause a faster 
driver loading. Since the FB is exactly the same except set to a 
different address, no tearing will occur.

Cheers,
~Maarten