2019-09-19 14:25:59

by Lucas Stach

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

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 <[email protected]>
>
> ---
>
> 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().

Regards,
Lucas

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

2019-09-19 14:26:11

by Philipp Puschmann

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 <[email protected]>
>>
>> ---
>>
>> 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;
>> }
>