linux-kernel - RE: [PATCH] dmaengine: remove DMA_MEMCPY

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Date:   Wed, 22 Jun 2022 18:34:57 +0000
From:   "Pandey, Radhey Shyam" <radhey.shyam.pandey@....com>
To:     Vinod Koul <vkoul@...nel.org>,
        Adrian Larumbe <adrianml@...mnos.upm.es>
CC:     Christoph Hellwig <hch@....de>,
        "michal.simek@...inx.com" <michal.simek@...inx.com>,
        "dmaengine@...r.kernel.org" <dmaengine@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>
Subject: RE: [PATCH] dmaengine: remove DMA_MEMCPY_SG once again

> -----Original Message-----
> From: Vinod Koul <vkoul@...nel.org>
> Sent: Tuesday, June 7, 2022 9:34 AM
> To: Adrian Larumbe <adrianml@...mnos.upm.es>
> Cc: Christoph Hellwig <hch@....de>; michal.simek@...inx.com;
> dmaengine@...r.kernel.org; linux-kernel@...r.kernel.org; linux-arm-
> kernel@...ts.infradead.org
> Subject: Re: [PATCH] dmaengine: remove DMA_MEMCPY_SG once again
> 
> On 06-06-22, 20:54, Adrian Larumbe wrote:
> > >On 06.06.2022 23:23, Vinod Koul wrote:
> > >On 06-06-22, 09:47, Christoph Hellwig wrote:
> > >> This was removed before due to the complete lack of users, but
> > >> 3218910fd585 ("dmaengine: Add core function and capability check
> > >> for
> > >> DMA_MEMCPY_SG") and 29cf37fa6dd9 ("dmaengine: Add consumer for
> the
> > >> new DMA_MEMCPY_SG API function.") added it back despite still not
> > >> having any users whatsoever.
> > >>
> > >> Fixes: 3218910fd585 ("dmaengine: Add core function and capability
> > >> check for DMA_MEMCPY_SG")
> > >> Fixes: 29cf37fa6dd9 ("dmaengine: Add consumer for the new
> > >> DMA_MEMCPY_SG API function.")
> > >
> > >This is consumer of the driver API and it was bought back with the
> > >premise that user will also come...
> >
> > It's commit 29cf37fa6dd9 ("dmaengine: Add consumer for the new
> > DMA_MEMCPY_SG API function.")
> >
> > The two previous commits add the new driver API callback and document it.
> >
> > >Adrianm, Michal any reason why user is not mainline yet..?

The dma client are use case dependent and mostly on end-users 
to upstream it. In the Xilinx tree, there is no CDMA  user apart from 
dmatest and as of now, there is no plan to support any other client.

It should be fine to revert this support again.

> >
> > Just double checked the mainline, and all three commits are there.
> 
> There are no clients in mainline which call this API. There is a driver which
> implements this API, but no users...
> 
> $ git grep dmaengine_prep_dma_memcpy_sg
> include/linux/dmaengine.h:static inline struct dma_async_tx_descriptor
> *dmaengine_prep_dma_memcpy_sg(
> 
> --
> ~Vinod