Re: [PATCH 3/3] videobuf2-core.h: Document the alloc memop size argument as page aligned

[Laurent Pinchart <laurent.pinchart@ideasonboard.com>]

Hi Sakari,

On Thursday, 13 December 2018 15:02:03 EET Sakari Ailus wrote:
> On Thu, Dec 13, 2018 at 02:59:50PM +0200, Laurent Pinchart wrote:
> > On Thursday, 13 December 2018 12:40:06 EET Sakari Ailus wrote:
> > > The size argument of the alloc memop, which allocates buffer memory, is
> > > page aligned. Document it as such, as code elsewhere has not taken this
> > > into account.
> > > 
> > > Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
> > > ---
> > > 
> > >  include/media/videobuf2-core.h | 3 ++-
> > >  1 file changed, 2 insertions(+), 1 deletion(-)
> > > 
> > > diff --git a/include/media/videobuf2-core.h
> > > b/include/media/videobuf2-core.h index e86981d615ae4..68b9fe660e4f1
> > > 100644
> > > --- a/include/media/videobuf2-core.h
> > > +++ b/include/media/videobuf2-core.h
> > > @@ -54,7 +54,8 @@ struct vb2_threadio_data;
> > >   *		will then be passed as @buf_priv argument to other ops in this
> > >   *		structure. Additional gfp_flags to use when allocating the
> > >   *		are also passed to this operation. These flags are from the
> > > - *		gfp_flags field of vb2_queue.
> > > + *		gfp_flags field of vb2_queue. The size argument to this function
> > > + *		shall be *page aligned*.
> > >   * @put:	inform the allocator that the buffer will no longer be used;
> > >   *		usually will result in the allocator freeing the buffer (if
> > >   *		no other users of this buffer are present); the @buf_priv
> > 
> > I wonder if a WARN_ON() to ensure this would make sense. In any case,
> 
> There's a single place where the alloc() op is called. I thought it'd be
> silly to put a check after the line of code that performs the alignment.

I was thinking about WARN_ON in the memory allocators, but if it's called from 
a single place, I agree it may not be needed. A comment in the dma-sg 
allocator would be useful though.

> Perhaps a comment right there?
> 
> I'm open to other ideas that don't seem silly. :-)

Stop calling my ideas silly :-)

> > Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>

-- 
Regards,

Laurent Pinchart