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    SubjectRe: [PATCH v2 1/2] i2c: add DMA support for freescale i2c driver
    Date
    On Thursday, March 06, 2014 at 06:02:03 AM, Yao Yuan wrote:
    > On Thu, March 06, 2014 at 12:44:14 PM, Marek Vasut wrote:
    > > On Thursday, March 06, 2014 at 05:36:14 AM, Yao Yuan wrote:
    > > > On Thu, March 06, 2014 at 11:23:50 AM, Marek Vasut wrote:
    > > > > On Wednesday, March 05, 2014 at 07:52:31 AM, Yuan Yao wrote:
    > > > > > Add dma support for i2c. This function depend on DMA driver.
    > > > > > You can turn on it by write both the dmas and dma-name properties
    > > > > > in dts node.
    > > > > >
    > > > > > Signed-off-by: Yuan Yao <yao.yuan@freescale.com>
    > > > > > ---
    > > > >
    > > > > [...]
    > > > >
    > > > > > @@ -601,6 +826,7 @@ static int i2c_imx_probe(struct
    > > > > > platform_device
    > > > >
    > > > > *pdev)
    > > > >
    > > > > > void __iomem *base;
    > > > > > int irq, ret;
    > > > > > u32 bitrate;
    > > > > >
    > > > > > + u32 phy_addr;
    > > > > >
    > > > > > dev_dbg(&pdev->dev, "<%s>\n", __func__);
    > > > > >
    > > > > > @@ -611,6 +837,7 @@ static int i2c_imx_probe(struct
    > > > > > platform_device
    > > > >
    > > > > *pdev)
    > > > >
    > > > > > }
    > > > > >
    > > > > > res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
    > > > > >
    > > > > > + phy_addr = res->start;
    > > > >
    > > > > Uh ... Shawn, I really think I am lost here. Don't you need to map
    > > > > this memory before you can use it for DMA ? The DMA mapping function
    > > > > should give you the physical address and is the right way to go
    > > > > about this instead of pulling the address from here, no ?
    > > > >
    > > > > I might be wrong here, I am rather uncertain, so please help me out.
    > > > > Thanks!
    > > >
    > > > Hi, Marek, Thanks for your suggestion.
    > > > Here you can review the code in include/linux/ioport.h The
    > > > resource->start describes the entity on the CPU bus as a starting
    > > > physical address. So I thinks it can used for dma directly.
    > >
    > > This doesn't feel right for some reason. If this is a register area, you
    > > should
    > > ioremap() it. If it's a memory area you do DMA to/from, you need to make
    > > sure you correctly flush/invalidate caches and properly handle the
    > > effects the write buffer might have. But I have a feeling you actually do
    > > DMA to/from register space here ?
    >
    > Yes, It's a register area. But I don't know why I should ioremap() it? It's
    > a bus address and DMA can use it directly. Is there some problem for my
    > understanding ?

    I am not too sure here, thus I am poking someone who can clearly answer this.

    Best regards,
    Marek Vasut


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