linux-kernel - Re: [PATCH v2] dma: imx-sdma: switch to dynamic context mode after script loaded

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Date:	Thu, 22 Jan 2015 08:28:39 +0100
From:	Sascha Hauer <s.hauer@...gutronix.de>
To:	Robin Gong <b38343@...escale.com>
Cc:	dan.j.williams@...el.com, vinod.koul@...el.com,
	dmaengine@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] dma: imx-sdma: switch to dynamic context mode after
 script loaded

On Thu, Jan 22, 2015 at 11:59:37AM +0800, Robin Gong wrote:
> Below comments got from Page4724 of Reference Manual of i.mx6q:
> http://cache.freescale.com/files/32bit/doc/ref_manual/IMX6DQRM.pdf
> 
> --"Static context mode should be used for the first channel called
> after reset to ensure that the all context RAM for that channel is
> initialized during the context SAVE phase when the channel is
> done or yields. Subsequent calls to the same channel or
> different channels may use any of the dynamic context modes.
> This will ensure that all context locations for the bootload
> channel are initialized, and prevent undefined values in context
> RAM from being loaded during the context restore if the
> channel is re-started later"
> 
> Unfortunately, the rule was broken by commit(5b28aa319bba96987316425a1131813d87cbab35)
> .This patch just take them back.
> 
> Signed-off-by: Robin Gong <b38343@...escale.com>
> ---
>  drivers/dma/imx-sdma.c | 11 ++++++++---
>  1 file changed, 8 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/dma/imx-sdma.c b/drivers/dma/imx-sdma.c
> index d0df198..d84b7a8 100644
> --- a/drivers/dma/imx-sdma.c
> +++ b/drivers/dma/imx-sdma.c
> @@ -330,6 +330,8 @@ struct sdma_engine {
>  	const struct sdma_driver_data	*drvdata;
>  };
>  
> +static bool channel0_first;

Nah, don't break the multi instance capability of drivers without a
reason. Don't use global static variables in driver context.

> +
>  static struct sdma_driver_data sdma_imx31 = {
>  	.chnenbl0 = SDMA_CHNENBL0_IMX31,
>  	.num_events = 32,
> @@ -531,6 +533,12 @@ static int sdma_run_channel0(struct sdma_engine *sdma)
>  		dev_err(sdma->dev, "Timeout waiting for CH0 ready\n");
>  	}
>  
> +	if (!channel0_first) {
> +		/* Set bits of CONFIG register with given context switching mode */
> +		writel_relaxed(SDMA_H_CONFIG_CSM, sdma->regs + SDMA_H_CONFIG);
> +		channel0_first = true;
> +	}

You don't need a variable. How about:

	if (readl(sdma->regs + SDMA_H_CONFIG) == 0)
		writel_relaxed(SDMA_H_CONFIG_CSM, sdma->regs + SDMA_H_CONFIG);

Sascha

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