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

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Message-ID: <20160124165631.GB7908@lukather>
Date:	Sun, 24 Jan 2016 17:56:31 +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-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

Hi,

On Sat, Jan 23, 2016 at 12:21:55PM +0800, Chen-Yu Tsai wrote:
> 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.

Ok. I've applied this patch and changed the commit log to remove the
voltage switching mention then, since it won't happen.

Thanks!
Maxime

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

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