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

From: radhey pandey <radheydmaengine@gmail.com>
To: Vinod Koul <vkoul@kernel.org>
Cc: Lars-Peter Clausen <lars@metafoo.de>,
	Adrian Larumbe <adrian.martinezlarumbe@imgtec.com>,
	dmaengine@vger.kernel.org, michal.simek@xilinx.com,
	linux-arm-kernel@lists.infradead.org, radheys@xilinx.com
Subject: Re: [PATCH 0/4] Expand Xilinx CDMA functions
Date: Tue, 1 Jun 2021 15:59:35 +0530	[thread overview]
Message-ID: <CAK8fcYC3Hdxas-5qUbXTi=a6VMXavt9O+yWn=1+8fPewehKy2w@mail.gmail.com> (raw)
In-Reply-To: <YIMB6DpM//wrPC6q@vkoul-mobl.Dlink>

On Fri, Apr 23, 2021 at 10:51 PM Vinod Koul <vkoul@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.
>
> > > 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