Re: [PATCH] dma-buf: add dma_data_direction to unmap dma_buf_op

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

Hi Daniel,

On Tuesday 31 January 2012 11:36:02 Daniel Vetter wrote:
> On Tue, Jan 31, 2012 at 10:42:59AM +0100, Laurent Pinchart wrote:
> > Hi Sumit,
> > 
> > > On Friday 27 January 2012 10:43:28 Sumit Semwal wrote:
> > [snip]
> > 
> > >  static inline void dma_buf_unmap_attachment(struct dma_buf_attachment
> > > 
> > > *attach,
> > > -                                            struct sg_table *sg)
> > > +                     struct sg_table *sg, enum dma_data_direction
> > > write)
> > 
> > On a second thought, would it make sense to store the direction in struct
> > dma_buf_attachment in dma_buf_map_attachment(), and pass the value
> > directly to the .unmap_dma_buf() instead of requiring the
> > dma_buf_unmap_attachment() caller to remember it ? Or is an attachment
> > allowed to map the buffer several times with different directions ?
> 
> Current dma api functions already require you to supply the direction
> argument on unmap

If I understand it correctly, that's mostly because the DMA API doesn't keep 
track of DMA mappings in a way that it can store the direction on map(), and 
use it on unmap(). In this case we have an attachment object that we can use 
to cache the information.

> and I think for cpu access I'm also leaning towards an interface where the
> importer has to supply the direction argument for both begin_access and
> end_access. So for consistency reasons I'm leaning towards adding it to
> unmap.

I'm OK with keeping the direction as an argument to unmap() if you think 
that's better.

-- 
Regards,

Laurent Pinchart