| Message ID | 1325750362-22598-3-git-send-email-richard.zhao@linaro.org |
|---|---|
| State | Changes Requested |
| Headers | show |
Hi Shawn, On Thu, Jan 05, 2012 at 05:23:17PM +0800, Shawn Guo wrote: > 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@linaro.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. Russel mentioned that too. But I cannot understand. If CONFIG_ARM_DMA_MEM_BUFFERABLE, readl/writel always call rmb/wmb. Do we realy need it? It might affect performance. Du to the concern, I didn't convert all the readl/writel. Thanks Richard > > -- > Regards, > Shawn > > _______________________________________________ > linux-arm-kernel mailing list > linux-arm-kernel@lists.infradead.org > http://lists.infradead.org/mailman/listinfo/linux-arm-kernel >
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@linaro.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.
On Thu, Jan 5, 2012 at 5:19 PM, Richard Zhao <richard.zhao@freescale.com> wrote: > Hi Shawn, > > On Thu, Jan 05, 2012 at 05:23:17PM +0800, Shawn Guo wrote: >> 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@linaro.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. > Russel mentioned that too. But I cannot understand. > If CONFIG_ARM_DMA_MEM_BUFFERABLE, readl/writel always call rmb/wmb. Do > we realy need it? It might affect performance. It's generally a good idea to use readl() and writel() unless it's performance critical, e.g. where endian conversion is not necessary and IO read/write order doesn't matter. As MT_DEVICE is strongly ordered, I think it'll be OK for __raw_{read,write}l() to be used for those ioremap() register accesses, not necessarily to those ioremap_*() version though.
On Thu, Jan 05, 2012 at 05:19:05PM +0800, Richard Zhao wrote: > Russel mentioned that too. But I cannot understand. > If CONFIG_ARM_DMA_MEM_BUFFERABLE, readl/writel always call rmb/wmb. Do > we realy need it? It might affect performance. > For safety, I think we need it. The operations should be really fast.
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); } /*
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@linaro.org> --- drivers/dma/imx-sdma.c | 2 +- 1 files changed, 1 insertions(+), 1 deletions(-)