linux-kernel - Re: [PATCH v1 1/2] at_hdmac: check and return DMA

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Message-ID: <d3d93452-70e6-72e5-b28e-1b259d1e489c@microchip.com>
Date:   Tue, 8 Nov 2022 11:50:19 +0000
From:   <Tudor.Ambarus@...rochip.com>
To:     <andriy.shevchenko@...ux.intel.com>, <vkoul@...nel.org>,
        <Nicolas.Ferre@...rochip.com>,
        <linux-arm-kernel@...ts.infradead.org>,
        <dmaengine@...r.kernel.org>, <linux-kernel@...r.kernel.org>
CC:     <Ludovic.Desroches@...rochip.com>
Subject: Re: [PATCH v1 1/2] at_hdmac: check and return DMA_PAUSED status when
 suitable

Hi, Andy,

On 11/8/22 09:49, Andy Shevchenko wrote:
> EXTERNAL EMAIL: Do not click links or open attachments unless you know the content is safe
> 
> device_tx_status() may return DMA_PAUSED status when driver supports it.

Yeah, but you haven't described the why. And that's because dma_cookie_status()
currently considers just DMA_COMPLETE and DMA_IN_PROGRESS for the status of the
cookie, so the controller drivers are forced to query the DMA_PAUSED state
themselves.

Also, I noticed that Vinod prefers that you use the full paragraph in the commit
message, and not a continuation of the patch title, so you may want to reword
the commit message.

> 
> Signed-off-by: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
> ---
>  drivers/dma/at_hdmac.c | 15 ++++++++++++++-
>  1 file changed, 14 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/dma/at_hdmac.c b/drivers/dma/at_hdmac.c
> index 8858470246e1..a9d8dd990d6e 100644
> --- a/drivers/dma/at_hdmac.c
> +++ b/drivers/dma/at_hdmac.c
> @@ -1669,9 +1669,19 @@ atc_tx_status(struct dma_chan *chan,
>         int ret;
> 
>         dma_status = dma_cookie_status(chan, cookie, txstate);
> -       if (dma_status == DMA_COMPLETE || !txstate)
> +       if (dma_status == DMA_COMPLETE)
>                 return dma_status;
> 
> +       /*
> +        * There's no point in calculating the residue if there's
> +        * no txstate to store the value.
> +        */
> +       if (!txstate) {
> +               if (test_bit(ATC_IS_PAUSED, &atchan->status))

there's a helper function that you can use instead: atc_chan_is_paused()

> +                       return DMA_PAUSED;
> +               return DMA_ERROR;

return dma_status please

> +       }
> +
>         spin_lock_irqsave(&atchan->vc.lock, flags);
>         /*  Get number of bytes left in the active transactions */
>         ret = atc_get_residue(chan, cookie, &residue);
> @@ -1684,6 +1694,9 @@ atc_tx_status(struct dma_chan *chan,
>                 dma_set_residue(txstate, residue);
>         }
> 
> +       if (test_bit(ATC_IS_PAUSED, &atchan->status))

The status may change after spin_unlock_irqrestore(). Should the residue
be in sync with the dma status? If yes, you should check the status while
holding the lock.

> +               dma_status = DMA_PAUSED;
> +
>         dev_vdbg(chan2dev(chan), "tx_status %d: cookie = %d residue = %u\n",
>                  dma_status, cookie, residue);
> 
> --
> 2.35.1
> 

-- 
Cheers,
ta