linux-kernel - Re: [PATCH v2 1/3] dmaengine: imx-sdma: fix buffer ownership

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Message-ID: <1b821b38-2206-07b3-eb0a-47b02bced95c@emlix.com>
Date:   Thu, 19 Sep 2019 12:34:57 +0200
From:   Philipp Puschmann <philipp.puschmann@...ix.com>
To:     Lucas Stach <l.stach@...gutronix.de>, linux-kernel@...r.kernel.org
Cc:     yibin.gong@....com, fugang.duan@....com, dan.j.williams@...el.com,
        vkoul@...nel.org, shawnguo@...nel.org, s.hauer@...gutronix.de,
        kernel@...gutronix.de, festevam@...il.com, linux-imx@....com,
        dmaengine@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v2 1/3] dmaengine: imx-sdma: fix buffer ownership

Hi Lucas,


Am 19.09.19 um 12:27 schrieb Lucas Stach:
> Hi Philipp,
> 
> On Do, 2019-09-19 at 12:23 +0200, Philipp Puschmann 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 possibility to get the buffer overwritten by SDMA
>> before
>> it has been processed by kernel leading to kind of random errors in
>> the
>> upper layers, e.g. bluetooth.
>>
>> Signed-off-by: Philipp Puschmann <philipp.puschmann@...ix.com>
>>
>> ---
>>
>> Changelog v2:
>>  - add dma_wb()
>>
>>  drivers/dma/imx-sdma.c | 4 +++-
>>  1 file changed, 3 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/dma/imx-sdma.c b/drivers/dma/imx-sdma.c
>> index 9ba74ab7e912..e029a2443cfc 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)
>>  		*/
>>  
>>  		desc->chn_real_count = bd->mode.count;
>> -		bd->mode.status |= BD_DONE;
>>  		bd->mode.count = desc->period_len;
>>  		desc->buf_ptail = desc->buf_tail;
>>  		desc->buf_tail = (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);
>>  
>> +		dma_wb();
> 
> Has this change been tested? The function you want here is called
> dma_wmb().
embarrassingly you are right. c&p error and even have not tried to build it :/
V3 comes soon..

Regards,
Philipp

> 
> Regards,
> Lucas
> 
>> +		bd->mode.status |= BD_DONE;
>> +
>>  		if (error)
>>  			sdmac->status = old_status;
>>  	}
>