Re: [PATCH] iio: buffer-dmaengine: adjust `bytes_used` with residue info

[Jonathan Cameron <jic23@kernel.org>]

On Sat, 29 Aug 2020 20:30:04 +0200
Lars-Peter Clausen <lars@metafoo.de> wrote:

> On 8/29/20 5:51 PM, Jonathan Cameron wrote:
> > On Wed, 26 Aug 2020 09:36:39 +0300
> > Alexandru Ardelean <ardeleanalex@gmail.com> wrote:
> >  
> >> On Wed, Aug 26, 2020 at 8:22 AM Lars-Peter Clausen <lars@metafoo.de> wrote:  
> >>> From: Alexandru Ardelean <alexandru.ardelean@analog.com>
> >>>
> >>> A transfer may fall shorter than the bytes in the block.
> >>> This information is available in the residue from the DMA engine, so we can
> >>> compute actual `bytes_used` with that by subtracting the residue.
> >>>     
> >> This was in my pipeline as well [obviously].
> >> Thanks :)
> >>  
> >>> Signed-off-by: Alexandru Ardelean <alexandru.ardelean@analog.com>
> >>> Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>  
> > "smells" like a fix.  Is it?  Or are we looking at something that
> > only matters for some future hardware, or an optmization?
> >
> > If it's a fix, where is the fixes tag?  
> 
> It's a feature :)
> 
> When we first added the IIO DMA buffer support this API did not exist in 
> dmaengine. So for the longest time most DMA drivers did not have the 
> ability to report short transfers. Primarily because in many cases the 
> hardware doesn't even support it.
> 
> Now with this patch the IIO DMA buffer implementation supports systems 
> where the DMA can generate short transfers.
Applied to the togreg branch of iio.git and pushed out as testing for
the autobuilders to play with it.

Thanks,

Jonathan

> 
> - Lars
>