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From:   Chen-Yu Tsai <wens@csie.org>
Date:   Wed, 28 Aug 2019 21:29:32 +0800
Message-ID: <CAGb2v67e8EiS-LUuhAyPc57nWd4iOBEWC_SZbH801Lzi4QWGyg@mail.gmail.com>
Subject: Re: [linux-sunxi] Re: [PATCH] mmc: sunxi: fix unusuable eMMC on some
 H6 boards by disabling DDR
To:     =?UTF-8?Q?Alejandro_Gonz=C3=A1lez?= 
        <alejandro.gonzalez.correo@gmail.com>
Cc:     Linus Walleij <linus.walleij@linaro.org>,
        Ulf Hansson <ulf.hansson@linaro.org>,
        Greg KH <gregkh@linuxfoundation.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        linux-mmc <linux-mmc@vger.kernel.org>,
        Linux ARM <linux-arm-kernel@lists.infradead.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        linux-sunxi <linux-sunxi@googlegroups.com>,
        Maxime Ripard <mripard@kernel.org>
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On Wed, Aug 28, 2019 at 8:52 PM Linus Walleij <linus.walleij@linaro.org> wrote:
>
> On Sun, Aug 25, 2019 at 5:06 PM Alejandro González
> <alejandro.gonzalez.correo@gmail.com> wrote:
>
> > Jernej Skrabec compared the BSP driver with this
> > driver, and found that the BSP driver configures pinctrl to operate at
> > 1.8 V when entering DDR mode (although 3.3 V operation is supported), while
> > the mainline kernel lacks any mechanism to switch voltages dynamically.

AFAIK The Pine H64 does not have the ability to switch I/O voltages. It is
fixed to either 1.8V (the default based on the schematics) or 3.3V.

> (...)
> > the kernel lacks the required
> > dynamic pinctrl control for now
>
> This is not a pin control thing, the I/O voltage level is usually
> controlled by a regulator called VCCQ, if the selection of the
> voltage rails is inside the pin control registers, see the solution
> in drivers/pinctrl/sh-pfc/pfc-sh73a0.c where we simply provide
> a regulator from inside the pinctrl driver to make things easy
> for the MMC core. Do this thing!

Or if it's simply voltage trimming for input, the a80 pinctrl driver
has something similar. Basically it registers a notifier on the
voltage rail supplying a set of pins, and toggles the register
to match the external voltage provided.

Unfortunately the user manual is quite vague on what it actually is.

> If you don't have time to fix it up properly right now I would slap
> in a big FIXME in the code so people know this needs
> to be fixed properly.

+1

ChenYu