linux-kernel - Re: [PATCH] mmc: sunxi: fix unusuable eMMC on some H6 boards by disabling DDR

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Date:   Wed, 28 Aug 2019 14:52:30 +0200
From:   Linus Walleij <linus.walleij@...aro.org>
To:     Alejandro González 
        <alejandro.gonzalez.correo@...il.com>
Cc:     Ulf Hansson <ulf.hansson@...aro.org>,
        Maxime Ripard <maxime.ripard@...tlin.com>,
        Chen-Yu Tsai <wens@...e.org>,
        Greg KH <gregkh@...uxfoundation.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-mmc <linux-mmc@...r.kernel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        linux-sunxi <linux-sunxi@...glegroups.com>
Subject: Re: [PATCH] mmc: sunxi: fix unusuable eMMC on some H6 boards by
 disabling DDR

On Sun, Aug 25, 2019 at 5:06 PM Alejandro González
<alejandro.gonzalez.correo@...il.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.
(...)
> 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!

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.

Yours,
Linus Walleij