Re: [PATCH 19/32] drm: Store a pointer to drm_format_info under drm_framebuffer

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Thu, Nov 17, 2016 at 08:06:10PM +0200, Ville Syrjälä wrote:
> On Thu, Nov 17, 2016 at 07:57:27PM +0200, Laurent Pinchart wrote:
> > Hi Ville,
> > 
> > Thank you for the patch.
> > 
> > On Thursday 17 Nov 2016 18:14:18 ville.syrjala@linux.intel.com wrote:
> > > From: Ville Syrjälä <ville.syrjala@linux.intel.com>
> > > 
> > > To avoid having to look up the format information struct every time,
> > > let's just store a pointer to it under drm_framebuffer.
> > > 
> > > Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
> > > ---
> > >  drivers/gpu/drm/drm_framebuffer.c    | 4 +++-
> > >  drivers/gpu/drm/drm_modeset_helper.c | 1 +
> > >  include/drm/drm_framebuffer.h        | 4 ++++
> > >  3 files changed, 8 insertions(+), 1 deletion(-)
> > > 
> > > diff --git a/drivers/gpu/drm/drm_framebuffer.c
> > > b/drivers/gpu/drm/drm_framebuffer.c index 527220c08f9b..47478678d609 100644
> > > --- a/drivers/gpu/drm/drm_framebuffer.c
> > > +++ b/drivers/gpu/drm/drm_framebuffer.c
> > > @@ -632,8 +632,10 @@ int drm_framebuffer_init(struct drm_device *dev, struct
> > > drm_framebuffer *fb, int ret;
> > > 
> > >  	INIT_LIST_HEAD(&fb->filp_head);
> > > -	if (WARN_ON_ONCE(fb->dev != dev))
> > > +	if (WARN_ON_ONCE(fb->dev != dev)) {
> > >  		fb->dev = dev;
> > > +		fb->format = drm_format_info(fb->pixel_format);
> > > +	}
> > 
> > 
> > With this drivers will start relying on fb->format. I believe we should commit 
> > to provide a non-NULL format info to avoid having to sprinkle NULL checks in 
> > all drivers. Should drm_framebuffer_init() return an error in that case ? Or 
> > do we guarantee already through another mean that the pixel format is valid 
> > and will always lead to a non-NULL format info here ?
> 
> I think for normal cases we already reject the NULL format info. I am a
> little worried that I might have missed some special case where that
> might not hold. But I'm not sure what would be the best way to guard
> against it. I really don't want to sprinkle NULL checks everywhere, and
> in fact I didn't.

And by normal I mean the addfb/addfb2 ioctls. Those will go through
framebuffer_check() which does:

info = __drm_format_info(...)
if (!info) {
	...
	return -EINVAL;
}

Well, you should know since you write the code ;)

So the more special cases of internally created fbs is where the danger
lies I think.

I guess we could have drm_framebuffer_init() return a failure (also
maybe in the fb->dev!=dev case?). That would at least protect all the
uses after drm_framebuffer_init(). And I guess the uses before _init()
are somewhat of a special case, and up to each driver to make sure that
it knows what it's doing if it has uses like that.

> 
> > 
> > >  	fb->funcs = funcs;
> > > 
> > >  	ret = drm_mode_object_get_reg(dev, &fb->base, DRM_MODE_OBJECT_FB,
> > > diff --git a/drivers/gpu/drm/drm_modeset_helper.c
> > > b/drivers/gpu/drm/drm_modeset_helper.c index 57a319e3f780..1aa5e3bcc8a1
> > > 100644
> > > --- a/drivers/gpu/drm/drm_modeset_helper.c
> > > +++ b/drivers/gpu/drm/drm_modeset_helper.c
> > > @@ -91,6 +91,7 @@ void drm_helper_mode_fill_fb_struct(struct drm_device
> > > *dev, }
> > > 
> > >  	fb->dev = dev;
> > > +	fb->format = info;
> > >  	fb->width = mode_cmd->width;
> > >  	fb->height = mode_cmd->height;
> > >  	for (i = 0; i < 4; i++) {
> > > diff --git a/include/drm/drm_framebuffer.h b/include/drm/drm_framebuffer.h
> > > index b3141a0e609b..741b3a994d1f 100644
> > > --- a/include/drm/drm_framebuffer.h
> > > +++ b/include/drm/drm_framebuffer.h
> > > @@ -122,6 +122,10 @@ struct drm_framebuffer {
> > >  	 */
> > >  	struct drm_mode_object base;
> > >  	/**
> > > +	 * @format: framebuffer format information
> > > +	 */
> > > +	const struct drm_format_info *format;
> > > +	/**
> > >  	 * @funcs: framebuffer vfunc table
> > >  	 */
> > >  	const struct drm_framebuffer_funcs *funcs;
> > 
> > -- 
> > Regards,
> > 
> > Laurent Pinchart
> 
> -- 
> Ville Syrjälä
> Intel OTC
> _______________________________________________
> dri-devel mailing list
> dri-devel@lists.freedesktop.org
> https://lists.freedesktop.org/mailman/listinfo/dri-devel

-- 
Ville Syrjälä
Intel OTC
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