linux-kernel - Re: [PATCH v1] dma: imx-sdma: switch to dynamic context mode after script loaded

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Date:	Tue, 20 Jan 2015 08:16:14 +0100
From:	Sascha Hauer <s.hauer@...gutronix.de>
To:	Robin Gong <b38343@...escale.com>
Cc:	vinod.koul@...el.com, dan.j.williams@...el.com,
	dmaengine@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1] dma: imx-sdma: switch to dynamic context mode after
 script loaded

On Tue, Jan 13, 2015 at 01:09:17PM +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 | 7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/dma/imx-sdma.c b/drivers/dma/imx-sdma.c
> index d0df198..510e463 100644
> --- a/drivers/dma/imx-sdma.c
> +++ b/drivers/dma/imx-sdma.c
> @@ -1323,6 +1323,10 @@ static void sdma_load_firmware(const struct firmware *fw, void *context)
>  	sdma_load_script(sdma, ram_code,
>  			header->ram_code_size,
>  			addr->ram_code_start_addr);
> +
> +	/* Set bits of CONFIG register with given context switching mode */
> +	writel_relaxed(SDMA_H_CONFIG_CSM, sdma->regs + SDMA_H_CONFIG);
> +

You move the CONFIG register initialization to a place which may never
be called. Look at the top of sdma_load_firmware:

	if (!fw) {
		dev_info(sdma->dev, "external firmware not found, using ROM firmware\n");
		/* In this case we just use the ROM firmware. */
		return;
	}

Sascha

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