Re: [PATCH v3] staging: android: ion: Add implementation of dma_buf_vmap and dma_buf_vunmap

[Alexey Skidanov]

On 01/31/2018 03:00 PM, Greg KH wrote:
> On Wed, Jan 31, 2018 at 02:03:42PM +0200, Alexey Skidanov wrote:
> > Any driver may access shared buffers, created by ion, using dma_buf_vmap and
> > dma_buf_vunmap dma-buf API that maps/unmaps previosuly allocated buffers into
> > the kernel virtual address space. The implementation of these API is missing in
> > the current ion implementation.
> >
> > Signed-off-by: Alexey Skidanov <alexey.skidanov@xxxxxxxxx>
> > ---
>
> No review from any other Intel developers? :(
Will add.
> Anyway, what in-tree driver needs access to these functions?
I'm not sure that there are the in-tree drivers using these functions 
and ion as buffer exporter because they are not implemented in ion :) 
But there are some in-tree drivers using these APIs (gpu drivers) with 
other buffer exporters.
> And are you sure that you don't need to do any "real" logic in the
> vmap/vunmap calls?  That feels like there would be some reference
> counting problems here.
dma_buf_start_cpu_access is called before the call to dma_buf_vmap. It 
actually increments the reference count. dma_buf_end_cpu_access is 
called after the dma_buf_vunmap. It actually decrements the reference 
count.>>
> > diff --git a/drivers/staging/android/ion/ion.c b/drivers/staging/android/ion/ion.c
> > index f480885..4f1dc7f 100644
> > --- a/drivers/staging/android/ion/ion.c
> > +++ b/drivers/staging/android/ion/ion.c
> > @@ -327,6 +327,17 @@ static void ion_dma_buf_kunmap(struct dma_buf *dmabuf, unsigned long offset,
> >   {
> >   }
> >   
> > +static void *ion_dma_buf_vmap(struct dma_buf *dmabuf)
> > +{
> > +	struct ion_buffer *buffer = dmabuf->priv;
> > +
> > +	return buffer->vaddr;
>
> Just call ion_dma_buf_kmap(dmabuf, 0)?
Sure.
> Again, please get this reviewed by someone else in Intel first.  Don't
> ignore the resources you have, to do so would be foolish :)
Sure. Will do.
> thanks,
>
> greg k-h

Thanks,
Alexey