Re: [PATCH v2] drm/panfrost: Document base field location constraint in panfrost_gem_object

[Boris Brezillon <boris.brezillon@collabora.com>]

On Fri, 29 Nov 2019 14:13:33 +0000
Steven Price <steven.price@arm.com> wrote:

> On 29/11/2019 13:56, Boris Brezillon wrote:
> > I've spent hours chasing a memory corruption that was caused by
> > insertion of an extra field field before ->base. Let's document the
> > fact that base has to be the first field in panfrost_gem_object.
> > 
> > Signed-off-by: Boris Brezillon <boris.brezillon@collabora.com>  
> 
> This seems to be a limitation imposed by the gem_create_object()
> callback - e.g. it's assumed that kfree() can be directly called on the
> result. Useful to have the documentation though.

Oh, you're right, I didn't catch that one.

> 
> Reviewed-by: Steven Price <steven.price@arm.com>
> 
> Steve
> 
> > ---
> > Changes in v2:
> > * Use the proper prefix in the subject line
> > ---
> >  drivers/gpu/drm/panfrost/panfrost_gem.h | 4 ++++
> >  1 file changed, 4 insertions(+)
> > 
> > diff --git a/drivers/gpu/drm/panfrost/panfrost_gem.h b/drivers/gpu/drm/panfrost/panfrost_gem.h
> > index b3517ff9630c..d480261fc177 100644
> > --- a/drivers/gpu/drm/panfrost/panfrost_gem.h
> > +++ b/drivers/gpu/drm/panfrost/panfrost_gem.h
> > @@ -10,6 +10,10 @@
> >  struct panfrost_mmu;
> >  
> >  struct panfrost_gem_object {
> > +	/*
> > +	 * Must be the first element because we're using some of the
> > +	 * drm_gem_shmem helpers.
> > +	 */
> >  	struct drm_gem_shmem_object base;
> >  	struct sg_table *sgts;
> >  
> >   
> 

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