[Intel-gfx] [PATCH] drm/i915: Remove src adjustment in intel_check_sprite_plane.

[Maarten Lankhorst]

Op 23-04-18 om 16:30 schreef Ville Syrjälä:
> On Mon, Apr 23, 2018 at 12:49:22PM +0200, Maarten Lankhorst wrote:
>> The rounding can cause a perfectly normal 16x16 src to full-screen
>> dst to be rounded down, even without clipping involved. Because of
>> this we should just remove the adjustment, as no other driver or plane
>> does it.
>>
>> Signed-off-by: Maarten Lankhorst <maarten.lankhorst at linux.intel.com>
>> ---
>>  drivers/gpu/drm/i915/intel_sprite.c | 5 -----
>>  1 file changed, 5 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/i915/intel_sprite.c b/drivers/gpu/drm/i915/intel_sprite.c
>> index a1d048af0261..203ca8b362a5 100644
>> --- a/drivers/gpu/drm/i915/intel_sprite.c
>> +++ b/drivers/gpu/drm/i915/intel_sprite.c
>> @@ -996,11 +996,6 @@ intel_check_sprite_plane(struct intel_plane *plane,
>>  			return vscale;
>>  		}
>>  
>> -		/* Make the source viewport size an exact multiple of the scaling factors. */
>> -		drm_rect_adjust_size(src,
>> -				     drm_rect_width(dst) * hscale - drm_rect_width(src),
>> -				     drm_rect_height(dst) * vscale - drm_rect_height(src));
>> -
> This makes the scaling factor checks a slightly incorrect. Ie. we might
> exceed the max h/vscale a bit without realizing it. It's a shame the
> hardware doesn't let us actually program the scaling factors/increments
> and starting phases anymore :( Also we don't actually know how the
> hardware calculates that stuff (assuming it has such things internally),
> so I'm not actually sure how we should be checking the max limit so
> that we actually check what the hardware will use.
>
> Without a more detailed study of the hardware behaviour I'm thinking
> we should perhaps just check the final src vs. dst coordinates like so:
> if (src > dst*max)
> 	fail;
> as that would avoid the precision issues with the .16 scaling factors.
>
> Another option could be to round h/vscale up. That should guarantee
> that we never exceed the max.
Could we take a pessimistic view for both sides? Round up if scaling > 1, round down when scaling < 1?
That way we should never be afraid of any limits..

~Maarten