Re: [igt-dev] [PATCH i-g-t v5 07/13] igt: fb: Don't pass the stride when allocating a dumb, multi-planar buffer

[Maxime Ripard <maxime.ripard@bootlin.com>]

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Hi!

On Tue, Jan 29, 2019 at 03:08:10PM -0500, Lyude Paul wrote:
> On Fri, 2019-01-25 at 15:58 +0100, Maxime Ripard wrote:
> > The dumb buffer allocation API only considers a single plane, and even
> > though allocating multi-planar buffers through it is allowed, the stride it
> > gives back is the the width times the bpp passed as an argument.
> > 
> > That doesn't work in our case, since the bpp is going to be the one we give
> > as an argument, but split over three planes so the stride doesn't match
> > anymore.
> > 
> > A proper fix for this would be to have a better dumb buffer allocation API,
> > but for the time being, let's do it that way.
> > 
> > Reviewed-by: Paul Kocialkowski <paul.kocialkowski@bootlin.com>
> > Signed-off-by: Maxime Ripard <maxime.ripard@bootlin.com>
> > ---
> >  lib/igt_fb.c | 17 ++++++++++++++++-
> >  1 file changed, 16 insertions(+), 1 deletion(-)
> > 
> > diff --git a/lib/igt_fb.c b/lib/igt_fb.c
> > index 1c52aebb674e..048d274e5d36 100644
> > --- a/lib/igt_fb.c
> > +++ b/lib/igt_fb.c
> > @@ -530,6 +530,7 @@ static int create_bo_for_fb(struct igt_fb *fb)
> >  {
> >  	const struct format_desc_struct *fmt = lookup_drm_format(fb-
> > >drm_format);
> >  	unsigned int plane, bpp;
> > +	unsigned *strides = &fb->strides[0];
> >  	int fd = fb->fd;
> >  
> >  	if (fb->tiling || fb->size || fb->strides[0] || igt_format_is_yuv(fb-
> > >drm_format)) {
> > @@ -575,8 +576,22 @@ static int create_bo_for_fb(struct igt_fb *fb)
> >  				    plane ? fmt->hsub * fmt->vsub : 1);
> >  
> >  	fb->is_dumb = true;
> > +
> > +	/*
> > +	 * We can't really pass the stride array here since the dumb
> > +	 * buffer allocation is assuming that it operates on one
> > +	 * plane, and therefore will calculate the stride as if each
> > +	 * pixels were stored on a single plane.
> 
> nitpick: s/each pixels were/each pixel was/
> 
> > +	 *
> > +	 * This might cause issues at some point on drivers that would
> > +	 * change the stride of YUV buffers, but we haven't
> > +	 * encountered any yet.
> > +	 */
> Is it possible to add an igt_assert to check for this? Either way, with those
> changes:

I'm not sure we can test this actually. If we don't pass any pointer,
then we don't get a stride back, and if we do then we will always get
a stride that is wrong for what we're trying to do :/

Maxime

-- 
Maxime Ripard, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com

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