linux-kernel - Re: [PATCH 1/2] drm/vram: store dumb bo dimensions.

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Date:   Wed, 26 Jun 2019 18:27:54 +0200
From:   Daniel Vetter <daniel@...ll.ch>
To:     Sam Ravnborg <sam@...nborg.org>
Cc:     Gerd Hoffmann <kraxel@...hat.com>,
        Maxime Ripard <maxime.ripard@...tlin.com>,
        open list <linux-kernel@...r.kernel.org>,
        dri-devel@...ts.freedesktop.org, David Airlie <airlied@...ux.ie>,
        tzimmermann@...e.de, Sean Paul <sean@...rly.run>
Subject: Re: [PATCH 1/2] drm/vram: store dumb bo dimensions.

On Wed, Jun 26, 2019 at 04:40:13PM +0200, Sam Ravnborg wrote:
> Hi Gerd.
> 
> On Wed, Jun 26, 2019 at 08:55:50AM +0200, Gerd Hoffmann wrote:
> > Store width and height of the bo.  Needed in case userspace
> > sets up a framebuffer with fb->width != bo->width..
> > 
> > Signed-off-by: Gerd Hoffmann <kraxel@...hat.com>
> > ---
> >  include/drm/drm_gem_vram_helper.h     | 1 +
> >  drivers/gpu/drm/drm_gem_vram_helper.c | 2 ++
> >  2 files changed, 3 insertions(+)
> > 
> > diff --git a/include/drm/drm_gem_vram_helper.h b/include/drm/drm_gem_vram_helper.h
> > index 1a0ea18e7a74..3692dba167df 100644
> > --- a/include/drm/drm_gem_vram_helper.h
> > +++ b/include/drm/drm_gem_vram_helper.h
> > @@ -39,6 +39,7 @@ struct drm_gem_vram_object {
> >  	struct drm_gem_object gem;
> >  	struct ttm_buffer_object bo;
> >  	struct ttm_bo_kmap_obj kmap;
> > +	unsigned int width, height;
> >  
> >  	/* Supported placements are %TTM_PL_VRAM and %TTM_PL_SYSTEM */
> >  	struct ttm_placement placement;
> > diff --git a/drivers/gpu/drm/drm_gem_vram_helper.c b/drivers/gpu/drm/drm_gem_vram_helper.c
> > index 4de782ca26b2..c02bf7694117 100644
> > --- a/drivers/gpu/drm/drm_gem_vram_helper.c
> > +++ b/drivers/gpu/drm/drm_gem_vram_helper.c
> > @@ -377,6 +377,8 @@ int drm_gem_vram_fill_create_dumb(struct drm_file *file,
> >  	gbo = drm_gem_vram_create(dev, bdev, size, pg_align, interruptible);
> >  	if (IS_ERR(gbo))
> >  		return PTR_ERR(gbo);
> > +	gbo->width = args->width;
> > +	gbo->height = args->height;
> >  
> >  	ret = drm_gem_handle_create(file, &gbo->gem, &handle);
> >  	if (ret)
> 
> Be warned, I may have missed something in the bigger picture.
> 
> Your patch will set width and height only for dumb bo's
> But we have several users of drm_gem_vram_create() that will
> not set the width and height.
> 
> So only in some cases can we rely on them being set.
> Should this be refactored so we always set width, height.
> Or maybe say in a small comment that width,height are only
> set for dumb bo's?

Also for dumb bo allocated buffers if userspace gets the dimensions wrong
between dumb_create and the addfb, something is wrong. Papering over that
by remembering the right dimensions doesn't look like a good solution.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch