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

From: Richard Zhao
Date: Tue Jan 03 2012 - 21:33:04 EST


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@xxxxxxxxxx>
> > ---
> > 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
>
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> linux-arm-kernel@xxxxxxxxxxxxxxxxxxx
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>

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