linux-kernel - Re: [PATCH v2 2/2] dma/imx-sdma: add wmb before enable a channel

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Message-ID: <20120104023157.GJ2414@b20223-02.ap.freescale.net>
Date:	Wed, 4 Jan 2012 10:31:58 +0800
From:	Richard Zhao <richard.zhao@...escale.com>
To:	Russell King - ARM Linux <linux@....linux.org.uk>
CC:	Richard Zhao <richard.zhao@...aro.org>, <patches@...aro.org>,
	<vinod.koul@...el.com>, <linux-kernel@...r.kernel.org>,
	<eric.miao@...aro.org>, <kernel@...gutronix.de>,
	<dan.j.williams@...el.com>, <shawn.guo@...aro.org>,
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v2 2/2] dma/imx-sdma: add wmb before enable a channel

On Tue, Jan 03, 2012 at 05:46:39PM +0000, Russell King - ARM Linux wrote:
> On Sun, Jan 01, 2012 at 10:38:12PM +0800, Richard Zhao wrote:
> > dma_alloc_coherent memory may be bufferable. We need to add
> > nececcary memory barrier.
> > 
> > Signed-off-by: Richard Zhao <richard.zhao@...aro.org>
> > ---
> >  drivers/dma/imx-sdma.c |    1 +
> >  1 files changed, 1 insertions(+), 0 deletions(-)
> > 
> > diff --git a/drivers/dma/imx-sdma.c b/drivers/dma/imx-sdma.c
> > index f8e87b5..9301bff 100644
> > --- a/drivers/dma/imx-sdma.c
> > +++ b/drivers/dma/imx-sdma.c
> > @@ -394,6 +394,7 @@ static int sdma_config_ownership(struct sdma_channel *sdmac,
> >  
> >  static void sdma_enable_channel(struct sdma_engine *sdma, int channel)
> >  {
> > +	wmb();
> >  	__raw_writel(1 << channel, sdma->regs + SDMA_H_START);
> 
> Use writel().  That's what it's there for:
> 
> #ifdef CONFIG_ARM_DMA_MEM_BUFFERABLE
> #define __iowmb()               wmb()
> #endif
> #define writel_relaxed(v,c)     ((void)__raw_writel((__force u32) \
>                                         cpu_to_le32(v),__mem_pci(c)))
> #define writel(v,c)             ({ __iowmb(); writel_relaxed(v,c); })
Why does writel always call wmb? ioremap memory needs mb too?
Isn't it supposed to be when there's prior touch of dma memory? 

Thanks
Richard
> 
> _______________________________________________
> linux-arm-kernel mailing list
> linux-arm-kernel@...ts.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
> 

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