linux-kernel - Re: [PATCH v2 1/2] dmaengine: stm32-mdma: align TLEN and buffer length on burst

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Date:   Wed, 11 Apr 2018 16:14:23 +0100
From:   Robin Murphy <robin.murphy@....com>
To:     Pierre-Yves MORDRET <pierre-yves.mordret@...com>,
        Vinod Koul <vinod.koul@...el.com>,
        Maxime Coquelin <mcoquelin.stm32@...il.com>,
        Alexandre Torgue <alexandre.torgue@...com>,
        Dan Williams <dan.j.williams@...el.com>,
        M'boumba Cedric Madianga <cedric.madianga@...il.com>,
        dmaengine@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/2] dmaengine: stm32-mdma: align TLEN and buffer
 length on burst

On 11/04/18 15:44, Pierre-Yves MORDRET wrote:
> Both buffer Transfer Length (TLEN if any) and transfer size have to be
> aligned on burst size (burst beats*bus width).
> 
> Signed-off-by: Pierre-Yves MORDRET <pierre-yves.mordret@...com>
> ---
>    Version history:
>      v1:
>         * Initial
>      v2:
> ---
> ---
>   drivers/dma/stm32-mdma.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/dma/stm32-mdma.c b/drivers/dma/stm32-mdma.c
> index daa1602..fbcffa2 100644
> --- a/drivers/dma/stm32-mdma.c
> +++ b/drivers/dma/stm32-mdma.c
> @@ -413,7 +413,7 @@ static u32 stm32_mdma_get_best_burst(u32 buf_len, u32 tlen, u32 max_burst,
>   	u32 best_burst = max_burst;
>   	u32 burst_len = best_burst * width;
>   
> -	while ((burst_len > 0) && (tlen % burst_len)) {
> +	while ((burst_len > 0) && (((tlen | buf_len) & (burst_len - 1)) != 0)) {
>   		best_burst = best_burst >> 1;
>   		burst_len = best_burst * width;
>   	}

FWIW, doesn't that whole loop come down to just:

	burst_len = min(ffs(tlen | buf_len), max_burst * width);

?

Robin.