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

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Message-ID: <CAGb2v66Ma7QmJpNO=Gv=ojrwL3n_MZm3H5XNKA2fpf_3AbOTBA@mail.gmail.com>
Date:	Sat, 23 Jan 2016 19:04:54 +0800
From:	Chen-Yu Tsai <wens@...e.org>
To:	Maxime Ripard <maxime.ripard@...e-electrons.com>
Cc:	Chen-Yu Tsai <wens@...e.org>, Ulf Hansson <ulf.hansson@...aro.org>,
	Hans de Goede <hdegoede@...hat.com>,
	"linux-mmc@...r.kernel.org" <linux-mmc@...r.kernel.org>,
	linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	linux-sunxi <linux-sunxi@...glegroups.com>
Subject: Re: [PATCH RFC 08/15] ARM: dts: sun6i: Add mmc3 pins for 8 bit emmc

Hi,

On Sat, Jan 23, 2016 at 4:31 AM, Maxime Ripard
<maxime.ripard@...e-electrons.com> wrote:
> 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.

All eMMC devices have a reset pin. The MMC standard specifies this as
one way to reset the card, others being a special reset command, or
powering the card off. It also notes a state when the card will not
accept commands, and will require a power cycle or asserting the reset
pin.

I assume all designs would route this pin. The FEX files also have this
pin included by default.


Regards
ChenYu