linux-kernel - Re: [PATCH 18/18] ipu3: Add driver for dummy INT3472 ACPI device

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Message-ID: <8c9e8818-6b5b-d5a5-b091-dab2d34ee0ee@gmail.com>
Date:   Thu, 3 Dec 2020 12:37:12 +0000
From:   Dan Scally <djrscally@...il.com>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>
Cc:     Sakari Ailus <sakari.ailus@...ux.intel.com>,
        linux-kernel@...r.kernel.org, linux-acpi@...r.kernel.org,
        linux-gpio@...r.kernel.org, linux-i2c@...r.kernel.org,
        linux-media@...r.kernel.org, devel@...ica.org, rjw@...ysocki.net,
        lenb@...nel.org, gregkh@...uxfoundation.org,
        mika.westerberg@...ux.intel.com, linus.walleij@...aro.org,
        bgolaszewski@...libre.com, wsa@...nel.org, yong.zhi@...el.com,
        bingbu.cao@...el.com, tian.shu.qiu@...el.com, mchehab@...nel.org,
        robert.moore@...el.com, erik.kaneda@...el.com, pmladek@...e.com,
        rostedt@...dmis.org, sergey.senozhatsky@...il.com,
        linux@...musvillemoes.dk, kieran.bingham+renesas@...asonboard.com,
        jacopo+renesas@...ndi.org,
        laurent.pinchart+renesas@...asonboard.com,
        jorhand@...ux.microsoft.com, kitakar@...il.com,
        heikki.krogerus@...ux.intel.com
Subject: Re: [PATCH 18/18] ipu3: Add driver for dummy INT3472 ACPI device

On 02/12/2020 15:08, Andy Shevchenko wrote:
> On Wed, Dec 02, 2020 at 02:42:28PM +0200, Laurent Pinchart wrote:
>> On Wed, Dec 02, 2020 at 01:09:56PM +0200, Sakari Ailus wrote:
>>> On Tue, Dec 01, 2020 at 08:37:58PM +0200, Laurent Pinchart wrote:
> 
> ...
> 
>> I think we should consider ACPI to be a hack in the first place :-)
> 
> I feel that about DT (and all chaos around it) but it's not a topic here.
> 
>>> Could this be just one more platform device for each of the three cases (or
>>> one for the two latter; I'm not quite sure yet)?
>>
>> Using MFD for this seems a bit overkill to me. I won't care much as I
>> won't maintain those drivers, but the current situation is complex
>> enough, it was hard for me to understand how things worked. Adding yet
>> another layer with another platform device won't make it any simpler.
>>
>> If we want to split this in two, I'd rather have a tps68470 driver on
>> one side, without ACPI op region support, but registering regulators,
>> GPIOs and clocks (without using separate drivers and devices for these
>> three features), and an INT3472 driver on the other side, with all the
>> ACPI glue and hacks. The tps68470 code could possibly even be structured
>> in such a way that it would be used as a library by the INT3472 driver
>> instead of requiring a separate platform device.
> 
> I'm afraid TPS68470 is MFD in hardware and its representation in the MFD is
> fine. What we need is to move IN3472 pieces out from it.
> 
> And I agree with your proposal in general.

Way back when I first joined this project we thought we needed i2c
drivers for driving the tps68470's clks and regulators. Tsuchiya found
some in an old Intel tree; they needed some minor tweaks but nothing
drastic. And I think they're designed to work with the mfd driver that's
already in the kernel.

So, can we do this by just checking (in a new
platform/x86/intel_skl_int3472.c) for a CLDB buffer in the PMIC, and
calling devm_mfd_add_devices() with either the GPIO and OpRegion drivers
(if no CLDB buffer found) or with the GPIO, clk and regulator drivers
(If there's a CLDB and it's not a discrete PMIC). Or else, using the
code from this patch directly in the platform driver if the CLDB says
it's a discrete PMIC?

>>> The GPIO regulator case is relatively safe, but the real PMICs require
>>> regulator voltage control as well as enabling and disabling the regulators.
>>> That probably requires either schematics or checking the register values at
>>> runtime on Windows (i.e. finding out which system you're dealing with, at
>>> runtime).
>