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

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Date:   Wed, 2 Dec 2020 14:38:02 +0000
From:   "Zulkifli, Muhammad Husaini" <muhammad.husaini.zulkifli@...el.com>
To:     Andy Shevchenko <andy.shevchenko@...il.com>,
        Ulf Hansson <ulf.hansson@...aro.org>
CC:     "Shevchenko, Andriy" <andriy.shevchenko@...el.com>,
        Linus Walleij <linus.walleij@...aro.org>,
        "Hunter, Adrian" <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 Mohamad, 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



>-----Original Message-----
>From: Andy Shevchenko <andy.shevchenko@...il.com>
>Sent: Wednesday, December 2, 2020 10:35 PM
>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>; Hunter, Adrian
><adrian.hunter@...el.com>; Michal Simek <michal.simek@...inx.com>; 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 Mohamad,
>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.

Maybe there is some misunderstanding regarding my statement in previous discussion.
I quoted "IO Pad" based on the statement in Databook CFG[1][10:7] for AON register.
From the Databook itself with additional confirmation from Keem Bay HW SOC Design Architect,
there is no direct control of these AON register bits from GPIO pads. 

>
>--
>With Best Regards,
>Andy Shevchenko