linux-kernel - Re: [PATCH v2] dmaengine: imx-sdma: Correct src_addr

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Date:   Thu, 14 Sep 2017 14:49:08 -0700
From:   Nicolin Chen <nicoleotsuka@...il.com>
To:     Fabio Estevam <festevam@...il.com>
Cc:     Vinod Koul <vinod.koul@...el.com>,
        Fabio Estevam <fabio.estevam@....com>,
        Dan Williams <dan.j.williams@...el.com>,
        dmaengine@...r.kernel.org,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] dmaengine: imx-sdma: Correct src_addr_widths and
 directions

On Thu, Sep 14, 2017 at 04:43:08PM -0300, Fabio Estevam wrote:
> Hi Nicolin,
> 
> On Thu, Sep 14, 2017 at 3:46 PM, Nicolin Chen <nicoleotsuka@...il.com> wrote:
> > The driver already supports DMA_DEV_TO_DEV in sdma_config(),
> > DMA_SLAVE_BUSWIDTH_2_BYTES and DMA_SLAVE_BUSWIDTH_1_BYTE in
> > sdma_prep_slave_sg(). So this patch adds them to the lists.
> >
> > Signed-off-by: Nicolin Chen <nicoleotsuka@...il.com>
> 
> Patch looks good.
> 
> Just curious: what is the specific usecase that triggered this change?

Any audio test case. The ASoC generic dmaengine gets the DMA
cap (4_BYTES only) and apply it to hw->formats in ASoC core.
SSI + WM8962 could have S8_LE, S16_LE and S24_LE formats but
it turns out that it only has S24_LE now because of this.

I haven't seen any side effect by DMA_DEV_TO_DEV yet but it
could potentially break ASRC once a similar constrain based
on the "directions" is applied.