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

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Date:   Fri, 25 Oct 2019 12:11:37 +0200
From:   Andrey Zhizhikin <andrey.z@...il.com>
To:     Hans de Goede <hdegoede@...hat.com>
Cc:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        lgirdwood@...il.com, broonie@...nel.org, 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

On Fri, Oct 25, 2019 at 11:38 AM Hans de Goede <hdegoede@...hat.com> wrote:
>
> Hi,
>
> On 25-10-2019 09:53, Andy Shevchenko wrote:
> > On Thu, Oct 24, 2019 at 02:29:37PM +0000, Andrey Zhizhikin wrote:
> >> This patchset introduces additional regulator driver for Intel Cherry
> >> Trail Whiskey Cove PMIC. It also adds a cell in mfd driver for this
> >> PMIC, which is used to instantiate this regulator.
> >>
> >> Regulator support for this PMIC was present in kernel release from Intel
> >> targeted Aero platform, but was not entirely ported upstream and has
> >> been omitted in mainline kernel releases. Consecutively, absence of
> >> regulator caused the SD Card interface not to be provided with Vqcc
> >> voltage source needed to operate with UHS-I cards.
> >>
> >> Following patches are addessing this issue and making sd card interface
> >> to be fully operable with UHS-I cards. Regulator driver lists an ACPI id
> >> of the SD Card interface in consumers and exposes optional "vqmmc"
> >> voltage source, which mmc driver uses to switch signalling voltages
> >> between 1.8V and 3.3V.
> >>
> >> This set contains of 2 patches: one is implementing the regulator driver
> >> (based on a non upstreamed version from Intel Aero), and another patch
> >> registers this driver as mfd cell in exising Whiskey Cove PMIC driver.
> >
> > Thank you.
> > Hans, Cc'ed, has quite interested in these kind of patches.
> > Am I right, Hans?
>
> Yes since I do a lot of work on Bay and Cherry Trail hw enablement I'm
> always interested in CHT specific patches.
>
> Overall this series looks good (from a high level view I did not
> do a detailed review) but I wonder if we really want to export all the
> regulators when we just need the vsdio one?

I thought about this point, and actually came to a personal conclusion
that if I do this as a new driver - then it is better to list all
possible regulators, creating some sort of "skeleton" which people
could then work on if need be. I do agree that at the present moment
the one regulator which is exposed is the one for vsdio, but listing
all possibilities should not hurt. This was my motivation to put them
all into the driver on the first place.

If you believe additional regulator elements should be removed from
this version of the driver - I can clean them up and come up with v2
here.

>
> Most regulators are controlled by either the P-Unit inside the CHT SoC
> or through ACPI OpRegion accesses.  Luckily the regulator subsys does not
> expose a sysfs interface for users to directly poke regulators, but this will
> still make it somewhat easier for users to poke regulators which they should
> leave alone.

Agree, this is a valid point. But honestly I would really be surprised
if a user would directly touch something which can burn his silicon to
pieces. Regulators are usually not approached by users; unless they
are really HW engineers and know what they are doing.

>
> Note I'm not saying this is wrong, having support for all regulators in place
> in case we need it in the future is also kinda nice. OTOH if we just need the
> one now, maybe we should just support the one for now ?

This I've already covered above I guess.

> Andrey, may I ask which device you are testing this on?

Sure, I use the original Intel Aero board. It used to have an official
image from Aero team with a heavily patched 4.4.y kernel, but when I
decided to have this updated to the latest stable branch - I've faced
the issue of missing core functionality, which led me to this patch.

>
> Anyways overall good work, thank you for doing this!

You're welcome, and thanks for looking into this!

>
> Regards,
>
> Hans
>

-- 
Regards,
Andrey.