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From:   Robin Gong <yibin.gong@nxp.com>
To:     Philipp Puschmann <philipp.puschmann@emlix.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
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Subject: RE: [PATCH v5 1/3] dmaengine: imx-sdma: fix buffer ownership
Thread-Topic: [PATCH v5 1/3] dmaengine: imx-sdma: fix buffer ownership
Thread-Index: AQHVchby6WsIv+QhqUqHYVdym6wSTaeqHbhA
Date:   Wed, 4 Dec 2019 09:19:59 +0000
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References: <20190923135808.815-1-philipp.puschmann@emlix.com>
 <20190923135808.815-2-philipp.puschmann@emlix.com>
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On 2019-9-23 Philipp Puschmann <philipp.puschmann@emlix.com> wrote:
> BD_DONE flag marks ownership of the buffer. When 1 SDMA owns the buffer,
> when 0 ARM owns it. When processing the buffers in
> sdma_update_channel_loop the ownership of the currently processed buffer
> was set to SDMA again before running the callback function of the buffer =
and
> while the sdma script may be running in parallel. So there was the possib=
ility to
> get the buffer overwritten by SDMA before it has been processed by kernel
Does this patch need indeed? I don't think any difference here move done fl=
ag
before callback or after callback, because callback never care this flag an=
d actually
done flag is setup for next time rather than this time. Basically, this fla=
g should be
set to 1 quickly asap so that sdma could use this bd asap. If delay the fla=
g may cause
sdma channel stop since all BDs consumed. Could you try again your case wit=
hout
this patch?
> leading to kind of random errors in the upper layers, e.g. bluetooth.
>=20
> Fixes: 1ec1e82f2510 ("dmaengine: Add Freescale i.MX SDMA support")
> Signed-off-by: Philipp Puschmann <philipp.puschmann@emlix.com>
> ---
>=20
> Changelog v5:
>  - no changes
>=20
> Changelog v4:
>  - fixed the fixes tag
>=20
> Changelog v3:
>  - use correct dma_wmb() instead of dma_wb()
>  - add fixes tag
>=20
> Changelog v2:
>  - add dma_wb()
>=20
>  drivers/dma/imx-sdma.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
>=20
> diff --git a/drivers/dma/imx-sdma.c b/drivers/dma/imx-sdma.c index
> 9ba74ab7e912..b42281604e54 100644
> --- a/drivers/dma/imx-sdma.c
> +++ b/drivers/dma/imx-sdma.c
> @@ -802,7 +802,6 @@ static void sdma_update_channel_loop(struct
> sdma_channel *sdmac)
>  		*/
>=20
>  		desc->chn_real_count =3D bd->mode.count;
> -		bd->mode.status |=3D BD_DONE;
>  		bd->mode.count =3D desc->period_len;
>  		desc->buf_ptail =3D desc->buf_tail;
>  		desc->buf_tail =3D (desc->buf_tail + 1) % desc->num_bd; @@ -817,6
> +816,9 @@ static void sdma_update_channel_loop(struct sdma_channel
> *sdmac)
>  		dmaengine_desc_get_callback_invoke(&desc->vd.tx, NULL);
>  		spin_lock(&sdmac->vc.lock);
>=20
> +		dma_wmb();
> +		bd->mode.status |=3D BD_DONE;
> +
>  		if (error)
>  			sdmac->status =3D old_status;
>  	}
> --
> 2.23.0