Re: [PATCH 6/7] drm/i915/skl: Update watermarks for Y tiling

[Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>]

On 02/24/2015 09:42 PM, Daniel Vetter wrote:
> On Mon, Feb 23, 2015 at 03:56:00PM +0000, Tvrtko Ursulin wrote:
>> From: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
>>
>> Display watermarks need different programming for different tiling
>> modes.
>>
>> Set the relevant flag so this happens during the plane commit and
>> add relevant data into a structure made available to the watermark
>> computation code.
>>
>> v2: Pass in tiling info to sprite plane updates as well.
>> v3: Rebased for plane handling changes.
>> v4: Handle fb == NULL when plane is disabled.
>> v5: Refactored for addfb2 interface.
>> v6: Refactored for fb modifier changes.
>> v7: Updated for atomic commit by only updating watermarks when tiling changes.
>>
>> Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
>> Acked-by: Ander Conselvan de Oliveira <ander.conselvan.de.oliveira@intel.com>
>> Acked-by: Matt Roper <matthew.d.roper@intel.com>
>> ---
>>   drivers/gpu/drm/i915/intel_display.c |  6 ++++++
>>   drivers/gpu/drm/i915/intel_drv.h     |  1 +
>>   drivers/gpu/drm/i915/intel_pm.c      | 33 ++++++++++++++++++++++++++++-----
>>   drivers/gpu/drm/i915/intel_sprite.c  |  6 ++++++
>>   4 files changed, 41 insertions(+), 5 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
>> index c622b11..74d4923 100644
>> --- a/drivers/gpu/drm/i915/intel_display.c
>> +++ b/drivers/gpu/drm/i915/intel_display.c
>> @@ -11985,6 +11985,12 @@ intel_check_primary_plane(struct drm_plane *plane,
>>   			INTEL_FRONTBUFFER_PRIMARY(intel_crtc->pipe);
>>
>>   		intel_crtc->atomic.update_fbc = true;
>> +
>> +		/* Update watermarks on tiling changes. */
>> +		if (!plane->state->fb || !state->base.fb ||
>> +		    plane->state->fb->modifier[0] !=
>> +		    state->base.fb->modifier[0])
>> +			intel_crtc->atomic.update_wm = true;
>
> Imo this is fragile. We should unconditionally recomupte watermarks imo
> and just ellide the hw update if nothing changed. Spending a few cpu
> cycles on this per frame shouldn't hurt, and it will avoid duplicated
> logic and checks for watermark recomputation splattered all over the code.
 >
> I know that it's kinda there already, but still minimal enough to patch
> up. But if Matt knows that this will get removed again with the two-stage
> wm code then I'm ok with leaving it in, with a FIXME comment added.

"Splattered all over the code" equals two places going to one when 
primary and sprite planes are unified.

I wouldn't wish for this to become an unbounded task since I am not sure 
it is not good enough as it is. I checked with Matt and Ander and they 
think it is good enough for now.

Not sure if FIXME is warranted here - to say what? That it will be 
refactored with the two-stage wm rewrite?

Regards,

Tvrtko
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