Re: [PATCH 1/3] drm/vc4: Set PPF scaling when the source image is only vertically scaled

From: Eric Anholt <eric@anholt.net>
To: Boris Brezillon <boris.brezillon@bootlin.com>
Cc: dri-devel@lists.freedesktop.org, stable@vger.kernel.org
Subject: Re: [PATCH 1/3] drm/vc4: Set PPF scaling when the source image is only vertically scaled
Date: Wed, 07 Nov 2018 09:08:02 -0800	[thread overview]
Message-ID: <87r2fwyfwt.fsf@anholt.net> (raw)
In-Reply-To: <20181024170238.4f65f5f2@bbrezillon>

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Boris Brezillon <boris.brezillon@bootlin.com> writes:

> On Wed, 24 Oct 2018 12:05:03 +0200
> Boris Brezillon <boris.brezillon@bootlin.com> wrote:
>
>> The source image might be only vertically scaled, and in this case
>> ->is_unity will be false, but we'd still have to force ->x_scaling[0]  
>> to VC4_SCALING_PPF for YUV conversion to work properly.
>> 
>> Let's replace the ->is_unity test by->x_scaling[0] == VC4_SCALING_NONE
>> to cope with that.
>> 
>> Fixes: 658d8cbd07da ("drm/vc4: Fix the "no scaling" case on multi-planar YUV formats")
>> Cc: <stable@vger.kernel.org>
>> Signed-off-by: Boris Brezillon <boris.brezillon@bootlin.com>
>> ---
>>  drivers/gpu/drm/vc4/vc4_plane.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>> 
>> diff --git a/drivers/gpu/drm/vc4/vc4_plane.c b/drivers/gpu/drm/vc4/vc4_plane.c
>> index 60d5ad19cedd..32b7b9f47c5d 100644
>> --- a/drivers/gpu/drm/vc4/vc4_plane.c
>> +++ b/drivers/gpu/drm/vc4/vc4_plane.c
>> @@ -318,7 +318,7 @@ static int vc4_plane_setup_clipping_and_scaling(struct drm_plane_state *state)
>>  		 * even on a plane that's otherwise 1:1. Looks like only PPF
>>  		 * works in that case, so let's pick that one.
>>  		 */
>> -		if (vc4_state->is_unity)
>> +		if (vc4_state->x_scaling[0] == VC4_SCALING_NONE)
>>  			vc4_state->x_scaling[0] = VC4_SCALING_PPF;
>
> Actually, I'm not sure about this patch is needed. According to the
> spec, we should not enable the scaler on the Y channel when ->is_unity
> is true.
> I tested it, and it seems to work if we just leave x_scaling[0] to
> VC4_SCALING_NONE.

Sorry, I've been delaying on this series until I could spend some time
looking at the spec.

I think you're right, I see no reason to kick us out of is_unity for
YUV -- you can have is_unity, Y unscaled, and UV scaled.

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