linux-kernel - Re: [PATCH RFC 09/15] ARM: dts: sun6i: sina31s: Switch to mmc3 for onboard eMMC

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Date:	Sat, 23 Jan 2016 12:21:55 +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 09/15] ARM: dts: sun6i: sina31s: Switch to mmc3 for
 onboard eMMC

On Sat, Jan 23, 2016 at 4:39 AM, Maxime Ripard
<maxime.ripard@...e-electrons.com> wrote:
> Hi,
>
> On Thu, Jan 21, 2016 at 01:26:36PM +0800, Chen-Yu Tsai wrote:
>> According to Allwinner, only mmc3 supports 8 bit DDR transfers for eMMC.
>> Switch to mmc3 for the onboard eMMC, and also assign vqmmc for signal
>> voltage sensing/switching, and "cap-mmc-hw-reset" to denote this
>> instance can use eMMC hardware reset.
>>
>> Signed-off-by: Chen-Yu Tsai <wens@...e.org>
>> ---
>>  arch/arm/boot/dts/sun6i-a31s-sina31s-core.dtsi | 6 ++++--
>>  1 file changed, 4 insertions(+), 2 deletions(-)
>>
>> diff --git a/arch/arm/boot/dts/sun6i-a31s-sina31s-core.dtsi b/arch/arm/boot/dts/sun6i-a31s-sina31s-core.dtsi
>> index ea69fb8ad4d8..4ec0c8679b2e 100644
>> --- a/arch/arm/boot/dts/sun6i-a31s-sina31s-core.dtsi
>> +++ b/arch/arm/boot/dts/sun6i-a31s-sina31s-core.dtsi
>> @@ -61,12 +61,14 @@
>>  };
>>
>>  /* eMMC on core board */
>> -&mmc2 {
>> +&mmc3 {
>>       pinctrl-names = "default";
>> -     pinctrl-0 = <&mmc2_8bit_emmc_pins>;
>> +     pinctrl-0 = <&mmc3_8bit_emmc_pins>;
>>       vmmc-supply = <&reg_dcdc1>;
>> +     vqmmc-supply = <&reg_dcdc1>;
>
> That seems odd. IIRC the VCC was supposed to be fixed and VCCQ could
> be either at 1.8 or 3V. Having the same regulator on both would make
> VCCQ forced to 3.3V, which seems to go against your commit log.
>
> What's the catch ? :)

That is how the board is routed. Which means the only use for
vqmmc-supply is the driver will know that it can only do 3.3V,
i.e. voltage sensing.

It is the reason I requested Olimex to look into this. Allwinner
reference designs all tie vqmmc directly to 3.3V.

Actually with the latest driver patches, this is not even needed. To
make the driver backward compatible, if no vqmmc-supply is given, it
just assumes 3.3V signaling.

Regards
ChenYu