linux-kernel - Re: [PATCH 0/2] add regulator driver and mfd cell for Intel Cherry Trail Whiskey Cove PMIC

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Date:   Mon, 28 Oct 2019 14:26:21 +0100
From:   Hans de Goede <hdegoede@...hat.com>
To:     Mark Brown <broonie@...nel.org>,
        Adrian Hunter <adrian.hunter@...el.com>
Cc:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Andrey Zhizhikin <andrey.z@...il.com>, lgirdwood@...il.com,
        lee.jones@...aro.org, linux-kernel@...r.kernel.org,
        Andrey Zhizhikin <andrey.zhizhikin@...ca-geosystems.com>
Subject: Re: [PATCH 0/2] add regulator driver and mfd cell for Intel Cherry
 Trail Whiskey Cove PMIC

Hi,

On 28-10-2019 13:45, Mark Brown wrote:
> On Mon, Oct 28, 2019 at 02:41:46PM +0200, Adrian Hunter wrote:
>> On 25/10/19 10:55 AM, Andy Shevchenko wrote:
> 
>>> Since it's about UHS/SD, Cc to Adrian as well.
> 
>> My only concern is that the driver might conflict with ACPI methods trying
>> to do the same thing, e.g. there is one ACPI SDHC instance from GPDWin DSDT
>> with code like this:

Oh, right that is a very good point.

> That's certainly what's idiomatic for ACPI (though machine specific
> quirks are too!).  The safe thing to do would be to only register the
> supply on systems where we know there's no ACPI method.

Right, so as I mentioned before Andrey told me about the evaluation
board he is using I was aware of only 3 Cherry Trail devices using
the Whiskey Cove PMIC. The GPD win, the GPD pocket and the Lenovo
Yoga book. I've checked the DSDT of all 3 and all 3 of them offer
voltage control through the Intel _DSM method for voltage control.

I've also actually tested this on the GPD win and 1.8V signalling
works fine there without needing Andrey's patch.

So it seems that Andrey's patch should only be active on his
dev-board, as actual production hardware ships with the _DSM method.

I believe that the best solution is for the Whiskey Cove MFD driver:
drivers/mfd/intel_soc_pmic_chtwc.c

To only register the new cell on Andrey's evaluation board model
(based in a DMI match I guess). Another option would be to do
the DMI check in the regulator driver, but that would mean
udev will needlessly modprobe the regulator driver on production
hardware, so doing it in the MFD driver and not registering the cell
seems best,

Regards,

Hans