linux-kernel - Re: [PATCH RFC 08/15] ARM: dts: sun6i: Add mmc3 pins for 8 bit emmc

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Message-ID: <20160122203138.GB3682@lukather>
Date:	Fri, 22 Jan 2016 21:31:38 +0100
From:	Maxime Ripard <maxime.ripard@...e-electrons.com>
To:	Chen-Yu Tsai <wens@...e.org>
Cc:	Ulf Hansson <ulf.hansson@...aro.org>,
	Hans de Goede <hdegoede@...hat.com>,
	linux-mmc@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org, linux-sunxi@...glegroups.com
Subject: Re: [PATCH RFC 08/15] ARM: dts: sun6i: Add mmc3 pins for 8 bit emmc

Hi, 

On Thu, Jan 21, 2016 at 01:26:35PM +0800, Chen-Yu Tsai wrote:
> mmc2 and mmc3 are available on the same pins, with different mux values.
> However, only mmc3 supports 8 bit DDR transfer modes.
> 
> Since preference for mmc3 over mmc2 is due to DDR transfer modes, just
> set the drive strength to 40mA, which is needed for DDR.
> 
> This pinmux setting also includes the hardware reset pin for emmc.
> 
> Signed-off-by: Chen-Yu Tsai <wens@...e.org>
> ---
>  arch/arm/boot/dts/sun6i-a31.dtsi | 10 ++++++++++
>  1 file changed, 10 insertions(+)
> 
> diff --git a/arch/arm/boot/dts/sun6i-a31.dtsi b/arch/arm/boot/dts/sun6i-a31.dtsi
> index b6ad7850fac6..1867af24ff52 100644
> --- a/arch/arm/boot/dts/sun6i-a31.dtsi
> +++ b/arch/arm/boot/dts/sun6i-a31.dtsi
> @@ -709,6 +709,16 @@
>  				allwinner,pull = <SUN4I_PINCTRL_NO_PULL>;
>  			};
>  
> +			mmc3_8bit_emmc_pins: mmc3@1 {
> +				allwinner,pins = "PC6", "PC7", "PC8", "PC9",
> +						 "PC10", "PC11", "PC12",
> +						 "PC13", "PC14", "PC15",
> +						 "PC24";
> +				allwinner,function = "mmc3";
> +				allwinner,drive = <SUN4I_PINCTRL_40_MA>;
> +				allwinner,pull = <SUN4I_PINCTRL_NO_PULL>;
> +			};
> +

Is that reset pin optional?

If so, I'd prefer it to be a separate node, like we're doing for the
SPI chip selects for example.

It allows more reusability between different devices without declaring
new nodes.

Thanks!
Maxime

-- 
Maxime Ripard, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com

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