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

From: Vinod Koul <vkoul@kernel.org>
To: Adrian Larumbe <adrian.martinezlarumbe@imgtec.com>
Cc: radhey pandey <radheydmaengine@gmail.com>,
	Lars-Peter Clausen <lars@metafoo.de>,
	dmaengine@vger.kernel.org, michal.simek@xilinx.com,
	linux-arm-kernel@lists.infradead.org, radheys@xilinx.com
Subject: Re: [EXTERNAL] Re: [PATCH 0/4] Expand Xilinx CDMA functions
Date: Mon, 5 Jul 2021 09:23:16 +0530	[thread overview]
Message-ID: <YOKCLNL/mLnYV6rp@matsya> (raw)
In-Reply-To: <20210702142310.vowvjanfwfivu45a@adrianlarumbe-HP-Elite-7500-Series-MT>

On 02-07-21, 15:23, Adrian Larumbe wrote:
> On 01.06.2021 15:59, radhey pandey wrote:
> > 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.
> 
> 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.

I guess I should start putting this regularly now! Yes it is okay to
bring dma sg support, provided
1. We have a user
2. the sematics of how that api works is well defined. Esp in the case where is src_sg and dstn_sg are different

Also, I would not accept patches which implement this in guise of a
different API.

Thanks

-- 
~Vinod