Re: [PATCH] dmaengine: stm32-mdma: correct desc prep when channel running

[Alain Volmat <alain.volmat@foss.st.com>]

Hi Amélie,

thanks a lot.

Tested-by: Alain Volmat <alain.volmat@foss.st.com>

Regards,
Alain

On Mon, Oct 09, 2023 at 10:24:50AM +0200, Amelie Delaunay wrote:
> From: Alain Volmat <alain.volmat@foss.st.com>
> 
> In case of the prep descriptor while the channel is already running, the
> CCR register value stored into the channel could already have its EN bit
> set.  This would lead to a bad transfer since, at start transfer time,
> enabling the channel while other registers aren't yet properly set.
> To avoid this, ensure to mask the CCR_EN bit when storing the ccr value
> into the mdma channel structure.
> 
> Fixes: a4ffb13c8946 ("dmaengine: Add STM32 MDMA driver")
> Signed-off-by: Alain Volmat <alain.volmat@foss.st.com>
> Signed-off-by: Amelie Delaunay <amelie.delaunay@foss.st.com>
> Cc: stable@vger.kernel.org
> ---
>  drivers/dma/stm32-mdma.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/dma/stm32-mdma.c b/drivers/dma/stm32-mdma.c
> index bae08b3f55c7..f414efdbd809 100644
> --- a/drivers/dma/stm32-mdma.c
> +++ b/drivers/dma/stm32-mdma.c
> @@ -489,7 +489,7 @@ static int stm32_mdma_set_xfer_param(struct stm32_mdma_chan *chan,
>  	src_maxburst = chan->dma_config.src_maxburst;
>  	dst_maxburst = chan->dma_config.dst_maxburst;
>  
> -	ccr = stm32_mdma_read(dmadev, STM32_MDMA_CCR(chan->id));
> +	ccr = stm32_mdma_read(dmadev, STM32_MDMA_CCR(chan->id)) & ~STM32_MDMA_CCR_EN;
>  	ctcr = stm32_mdma_read(dmadev, STM32_MDMA_CTCR(chan->id));
>  	ctbr = stm32_mdma_read(dmadev, STM32_MDMA_CTBR(chan->id));
>  
> @@ -965,7 +965,7 @@ stm32_mdma_prep_dma_memcpy(struct dma_chan *c, dma_addr_t dest, dma_addr_t src,
>  	if (!desc)
>  		return NULL;
>  
> -	ccr = stm32_mdma_read(dmadev, STM32_MDMA_CCR(chan->id));
> +	ccr = stm32_mdma_read(dmadev, STM32_MDMA_CCR(chan->id)) & ~STM32_MDMA_CCR_EN;
>  	ctcr = stm32_mdma_read(dmadev, STM32_MDMA_CTCR(chan->id));
>  	ctbr = stm32_mdma_read(dmadev, STM32_MDMA_CTBR(chan->id));
>  	cbndtr = stm32_mdma_read(dmadev, STM32_MDMA_CBNDTR(chan->id));
> -- 
> 2.25.1
>