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

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Date:   Fri, 8 Jan 2021 23:24:44 +0000
From:   Daniel Scally <djrscally@...il.com>
To:     Andy Shevchenko <andy.shevchenko@...il.com>
Cc:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        linux-i2c <linux-i2c@...r.kernel.org>,
        Linux Media Mailing List <linux-media@...r.kernel.org>,
        devel@...ica.org, "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Len Brown <lenb@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>,
        Linus Walleij <linus.walleij@...aro.org>,
        Bartosz Golaszewski <bgolaszewski@...libre.com>,
        Wolfram Sang <wsa@...nel.org>, Yong Zhi <yong.zhi@...el.com>,
        Sakari Ailus <sakari.ailus@...ux.intel.com>,
        Bingbu Cao <bingbu.cao@...el.com>,
        Tian Shu Qiu <tian.shu.qiu@...el.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Robert Moore <robert.moore@...el.com>,
        Erik Kaneda <erik.kaneda@...el.com>,
        Petr Mladek <pmladek@...e.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        kieran.bingham+renesas@...asonboard.com,
        Jacopo Mondi <jacopo+renesas@...ndi.org>,
        Laurent Pinchart <laurent.pinchart+renesas@...asonboard.com>,
        Jordan Hand <jorhand@...ux.microsoft.com>,
        Tsuchiya Yuto <kitakar@...il.com>,
        "Krogerus, Heikki" <heikki.krogerus@...ux.intel.com>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>
Subject: Re: [PATCH 18/18] ipu3: Add driver for dummy INT3472 ACPI device

Hi Andy

On 08/01/2021 12:17, Andy Shevchenko wrote:
> On Fri, Jan 8, 2021 at 1:56 AM Daniel Scally <djrscally@...il.com> wrote:
>> On 30/11/2020 20:07, Andy Shevchenko wrote:
>>> On Mon, Nov 30, 2020 at 01:31:29PM +0000, Daniel Scally wrote:
> ...
>
>>> It's solely Windows driver design...
>>> Luckily I found some information and can clarify above table:
>>>
>>> 0x00 Reset
>>> 0x01 Power down
>>> 0x0b Power enable
>>> 0x0c Clock enable
>>> 0x0d LED (active high)
>>>
>>> The above text perhaps should go somewhere under Documentation.
>> Coming back to this; there's a bit of an anomaly with the 0x01 Power
>> Down pin for at least one platform.  As listed above, the OV2680 on one
>> of my platforms has 3 GPIOs defined, and the table above gives them as
>> type Reset, Power down and Clock enable. I'd assumed from this table
>> that "power down" meant a powerdown GPIO (I.E. the one usually called
>> PWDNB in Omnivision datasheets and "powerdown" in drivers), but the
>> datasheet for the OV2680 doesn't list a separate reset and powerdown
>> pin, but rather a single pin that performs both functions.
> All of them are GPIOs, the question here is how they are actually
> connected on PCB level and I have no answer to that. You have to find
> schematics somewhere.

Yeah; I've been trying to get those but so far, no dice.

>
>> Am I wrong to treat that as something that ought to be mapped as a
>> powerdown GPIO to the sensors? Or do you know of any other way to
>> reconcile that discrepancy?
> The GPIOs can go directly to the sensors or be a control pin for
> separate discrete power gates.
> So, we can do one of the following:
>  a) present PD GPIO as fixed regulator;
>  b) present PD & Reset GPIOs as regulator;
>  c) provide them as is to the sensor and sensor driver must do what it
> considers right.
>
> Since we don't have schematics (yet?) and we have plenty of variations
> of sensors, I would go to c) and update the driver of the affected
> sensor as needed. Because even if you have separate discrete PD for
> one sensor on one platform there is no guarantee that it will be the
> same on another. Providing a "virtual" PD in a sensor that doesn't
> support it is the best choice I think. Let's hear what Sakari and
> other experienced camera sensor developers say.
>
> My vision is purely based on electrical engineering background,
> experience with existing (not exactly camera) sensor drivers and
> generic cases.

Alright; thanks. I'm happy with C being the answer, so unless someone
thinks differently I'll work on that basis.

>> Failing that; the only way I can think to handle this is to register
>> proxy GPIO pins assigned to the sensors as you suggested previously, and
>> have them toggle the GPIO's assigned to the INT3472 based on platform
>> specific mapping data (I.E. we register a pin called "reset", which on
>> most platforms just toggles the 0x00 pin, but on this specific platform
>> would drive both 0x00 and 0x01 together. We're already heading that way
>> for the regulator consumer supplies so it's sort of nothing new, but I'd
>> still rather not if it can be avoided.
>