linux-kernel - Re: [PATCH v3 2/2] dma/imx-sdma: use writel to write register when enable a channel

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Date:	Thu, 5 Jan 2012 17:23:17 +0800
From:	Shawn Guo <shawn.guo@...aro.org>
To:	Richard Zhao <richard.zhao@...aro.org>
Cc:	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	dan.j.williams@...el.com, vinod.koul@...el.com,
	kernel@...gutronix.de, eric.miao@...aro.org, patches@...aro.org,
	Arnd Bergmann <arnd@...db.de>
Subject: Re: [PATCH v3 2/2] dma/imx-sdma: use writel to write register when
 enable a channel

On Thu, Jan 05, 2012 at 03:59:22PM +0800, Richard Zhao wrote:
> dma_alloc_coherent memory may be bufferable when set
> CONFIG_ARM_DMA_MEM_BUFFERABLE. We need to add nececcary
> memory barrier. writel implicitly call wmb in such case.
> 
> Signed-off-by: Richard Zhao <richard.zhao@...aro.org>
> ---
>  drivers/dma/imx-sdma.c |    2 +-
>  1 files changed, 1 insertions(+), 1 deletions(-)
> 
> diff --git a/drivers/dma/imx-sdma.c b/drivers/dma/imx-sdma.c
> index c2bc4f1..e987468 100644
> --- a/drivers/dma/imx-sdma.c
> +++ b/drivers/dma/imx-sdma.c
> @@ -396,7 +396,7 @@ static int sdma_config_ownership(struct sdma_channel *sdmac,
>  
>  static void sdma_enable_channel(struct sdma_engine *sdma, int channel)
>  {
> -	__raw_writel(1 << channel, sdma->regs + SDMA_H_START);
> +	writel(1 << channel, sdma->regs + SDMA_H_START);
>  }
>  

As educated by Arnd, generally it's safer to use pair of readl/writel
than __raw_readl/__raw_writel in driver.  I'm wondering if it's a good
opportunity for us to change the pair all over this driver.

-- 
Regards,
Shawn
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