Re: [PATCHv4 1/4] arm: dts: Add support for SD/MMC on SOCFPGA

[Arnd Bergmann <arnd@arndb.de>]

On Thursday 05 December 2013, dinguyen@altera.com wrote:
> From: Dinh Nguyen <dinguyen@altera.com>
> 
> Re-use the "rockchip,rk2928-dw-mshc" binding that will support SD/MMC on
> Altera's SOCFPGA platform.
> 
> Signed-off-by: Dinh Nguyen <dinguyen@altera.com>
> ---
> v3: Re-use "rockchip,rk2928-dw-mshc" binding
> v3: none
> v2: none
> ---
>  arch/arm/boot/dts/socfpga.dtsi          |   11 +++++++++++
>  arch/arm/boot/dts/socfpga_arria5.dtsi   |   12 ++++++++++++
>  arch/arm/boot/dts/socfpga_cyclone5.dtsi |   12 ++++++++++++
>  arch/arm/boot/dts/socfpga_vt.dts        |   12 ++++++++++++
>  4 files changed, 47 insertions(+)
> 
> diff --git a/arch/arm/boot/dts/socfpga.dtsi b/arch/arm/boot/dts/socfpga.dtsi
> index f936476..3d9f01b 100644
> --- a/arch/arm/boot/dts/socfpga.dtsi
> +++ b/arch/arm/boot/dts/socfpga.dtsi
> @@ -469,6 +469,17 @@
>  			cache-level = <2>;
>  		};
>  
> +		mmc: dwmmc0@ff704000 {
> +			compatible = "rockchip,rk2928-dw-mshc";
> +			reg = <0xff704000 0x1000>;
> +			interrupts = <0 139 4>;
> +			fifo-depth = <0x400>;
> +			#address-cells = <1>;
> +			#size-cells = <0>;
> +			clocks = <&l4_mp_clk>, <&sdmmc_clk>;
> +			clock-names = "biu", "ciu";
> +		};


I think it's great that you can reuse the existing driver, but I'd recommend
using a generic compatible string here in addition to one that identifies
your specific implementation. You can list "rockchip,rk2928-dw-mshc" as
well, but that is probably not necessary.

What I'd expect to see here is either

	compatible = "altr,socfpga-dw-mshc", "rockchip,rk2928-dw-mshc", "snps,dw-mshc";

or 

	compatible = "altr,socfpga-dw-mshc", "rockchip,rk2928-dw-mshc", "snps,dw-mshc";


It's probably not too late to generalize the SDMMC_CMD_USE_HOLD_REG
handling, which is currently the only difference between the generic
"snps,dw-mshc" and the newer "rockchip,rk2928-dw-mshc" variant.

It's quite likely that all implementations should actually set
SDMMC_CMD_USE_HOLD_REG (if both rockchips and altera set it) and you
don't need to have any distinction in the dw_mmc-pltfm.c driver at all.

If it's actually needed on some but not others, you could add a binary
DT property to tell the driver about it rather than keying it off of
the compatible string. If it's needed only on older (or only on newer)
versions of the dw-mshc design, it could be encoded as a version in the
string, such as "snps,dw-mshc-1.234".

	Arnd