[EXTERNAL] Re: [PATCH 0/4] Expand Xilinx CDMA functions

[Adrian Larumbe]

On 01.06.2021 15:59, radhey pandey wrote:
> On Fri, Apr 23, 2021 at 10:51 PM Vinod Koul <vkoul at kernel.org> wrote:
> >
> > On 23-04-21, 15:51, Lars-Peter Clausen wrote:
> > > On 4/23/21 3:24 PM, Vinod Koul wrote:
> > > > On 23-04-21, 11:17, Lars-Peter Clausen wrote:
> > > > > It seems to me what we are missing from the DMAengine API is the equivalent
> > > > > of device_prep_dma_memcpy() that is able to take SG lists. There is already
> > > > > a memset_sg, it should be possible to add something similar for memcpy.
> > > > You mean something like dmaengine_prep_dma_sg() which was removed?
> > > >
> > > Ah, that's why I could have sworn we already had this!
> >
> > Even at that time we had the premise that we can bring the API back if
> > we had users. I think many have asked for it, but I havent seen a patch
> > with user yet :)
> Right.  Back then we had also discussed bringing the dma_sg API
> but the idea was dropped as we didn't had a xilinx/any consumer
> client driver for it in the mainline kernel.
> 
> I think it's the same state now.

Would it be alright if I brought back the old DMA_SG interface that was removed
in commit c678fa66341c?  It seems that what I've effectively done is
implementing the semantics of that API call under the guise of
dma_prep_slave. However I still need mem2mem SG transfer support on CDMA, which
seems long gone from the driver, even though the HW does offer it.

If people are fine with it I can restore that interface and CDMA as the sole consumer.

>
> > > static inline struct dma_async_tx_descriptor *dmaengine_prep_dma_sg(
> > >                 struct dma_chan *chan,
> > >                 struct scatterlist *dst_sg, unsigned int dst_nents,
> > >                 struct scatterlist *src_sg, unsigned int src_nents,
> > >                 unsigned long flags)
> > >
> > > The problem with this API is that it would work only when src_sg and
> > > dst_sg is of similar nature, if not then how should one go about
> > > copying...should we fill without a care for dst_sg being different than
> > > src_sg as long as total data to be copied has enough space in dst...
> > At least for the CDMA the only requirement is that both buffers have the
> > same total size.
>
> I will merge if with a user but semantics need to be absolutely clear on
> what is allowed and not, do I hear a volunteer ?
> --
> ~Vinod