On Tue, Jul 02, 2013 at 11:43:13AM +0100, Huang Shijie wrote:

? 2013?07?02? 17:56, Mark Rutland ??:

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On Tue, Jul 02, 2013 at 07:30:26AM +0100, Huang Shijie wrote:

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 The imx6 uart can supports the DMA, imx uart driver has added a new
 compatible property for the imx6 uart.
 
 In order to enable the DMA for some uart port in imx6, we rename the
 uart's compatible property to "fsl,imx6-uart".

Doesn't this change break using these dts with an older kernel? You

is it reasonable to use a new dts with an old kernel?

As long as everything required to boot is described in a fashion the old
kernel understands, I see no reason it shouldn't be. I certainly see no
reason to break compatibility with an old kernel by *removing* a
compatible string ("fsl,imx21-uart") that should not break newer
kernels if they choose to use the more-specific compatible string.

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remove the "fsl,imx21-uart" string older kernels understand.

Given you already had "fsl,imx6q-uart" and "fsl,imx6sl-uart" strings,
would it not have made more sense to just add these to the driver?

I think it's not a good idea.

Are there instances of "fsl-imx6q-uart" or "fsl,imx6sl-uart" that aren't
compatible with this new "fsl,imx6-uart" (i.e. are any not DMA capable)?

If not, then using the existing binding gives the same behaviour without
confusing everyone by adding a slightly different compatible string,
without the churn caused by modifying the dts, and the cost to Linux is
a single line. Boards with a pre-built dtb will get the new
functionality by just changing the Linux image.

I don't see what's wrong with this.

Thanks,
Mark.

Shawn, what's your opinion about this?

thanks
Huang Shijie