linux-kernel - Re: [PATCH v6 0/4] mmc: sdhci-of-arasan: Enable UHS-1 support for Keem Bay SOC

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Message-ID: <CAHp75Vf66eWnJFom66oZZnZ4Rcw0VF0QkGWgM5Mm40mTVt6i4A@mail.gmail.com>
Date:   Wed, 2 Dec 2020 16:34:44 +0200
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Ulf Hansson <ulf.hansson@...aro.org>
Cc:     "Shevchenko, Andriy" <andriy.shevchenko@...el.com>,
        Linus Walleij <linus.walleij@...aro.org>,
        "Zulkifli, Muhammad Husaini" <muhammad.husaini.zulkifli@...el.com>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Michal Simek <michal.simek@...inx.com>,
        "linux-mmc@...r.kernel.org" <linux-mmc@...r.kernel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "Raja Subramanian, Lakshmi Bai" 
        <lakshmi.bai.raja.subramanian@...el.com>,
        Wan Ahmad Zainie <wan.ahmad.zainie.wan.mohamad@...el.com>,
        Mark Gross <mgross@...ux.intel.com>
Subject: Re: [PATCH v6 0/4] mmc: sdhci-of-arasan: Enable UHS-1 support for
 Keem Bay SOC

On Wed, Dec 2, 2020 at 4:10 PM Ulf Hansson <ulf.hansson@...aro.org> wrote:
> On Wed, 2 Dec 2020 at 14:09, Andy Shevchenko <andy.shevchenko@...il.com> wrote:
> > On Wed, Dec 2, 2020 at 2:44 PM Ulf Hansson <ulf.hansson@...aro.org> wrote:

...

> > My point is that it may be *not* a pin control at all.
>
> Sorry, but I don't quite follow, what is *not* a pinctrl?
>
> According to the information I have received from the previous
> discussions [1], it's clear to me that the ARM SMC call ends up
> changing settings for the I/O-pads. Or did I get that wrong?

I'm discussing the possible implication of the solution (faking pin
control) you are proposing.
In this case we know that it's a pin control *under the hood of IPC*
(!) but in another hardware generation it may be, for example,custom
voltage regulator.

What you are proposing seems to me suboptimal and actually lying about
hardware. Because we do not have direct access to control this pad.
What we have is an IPC to firmware. And it's not our business what is
under the hood.

It seems it was a mistake to talk about these details in the first
place because it brings more confusion about hardware. So, consider
that it's not a pin control from OS perspective, but a firmware magic.

-- 
With Best Regards,
Andy Shevchenko