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

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Message-ID: <efd0ae7a-4ba2-e02e-6111-7f3d382d1eac@gmail.com>
Date:   Tue, 1 Dec 2020 21:05:11 +0000
From:   Dan Scally <djrscally@...il.com>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>
Cc:     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,
        sakari.ailus@...ux.intel.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,
        Hans de Goede <hdegoede@...hat.com>
Subject: Re: [PATCH 18/18] ipu3: Add driver for dummy INT3472 ACPI device


On 01/12/2020 19:21, Andy Shevchenko wrote:
> On Tue, Dec 01, 2020 at 09:06:38PM +0200, Laurent Pinchart wrote:
>> On Tue, Dec 01, 2020 at 09:05:23PM +0200, Andy Shevchenko wrote:
>>> On Tue, Dec 01, 2020 at 08:55:48PM +0200, Laurent Pinchart wrote:
>>>
>>>> Do you think the Windows driver would use DMI ?
>>> Linux is using DMI for quirks.
>>>
>>>> That seems quite
>>>> unlikely to me, given how they would have to release a new driver binary
>>>> for every machine. I'm pretty sure that a different mechanism is used to
>>>> identify camera integration, and I think it would make sense to follow
>>>> the same approach. That would allow us to avoid large tables of DMI
>>>> identifiers that would need to be constently updated, potentially making
>>>> user experience better.
>>> All Surface family can be matched in a way as Apple machines [1].
>>>
>>> [1]: https://lkml.org/lkml/2020/4/15/1198
>> But not all Surface machines necessarily have the same camera
>> architecture. My point is that there seems to be identifiers reported in
>> ACPI for the exact purpose of identifying the camera architecture. If we
>> used DMI instead, we would have to handle each machine individually.
> With help of DMI we may narrow down the search.
>
> But again, we are talking about uncertainity. It may be your way (a lot of
> platforms that have different settings), or mine (only a few with more or less
> standard sets of settings).
>
> DMI is simply standard in Linux (people usually easier can grep for quirks for
> a specific platform).
>
> I would rather ask Hans' opinion since he has quite an expertise with DMI for
> good and bad.
>
I have no real preference as to the current method or DMI, but thoughts
that come to mind are:


1. given your info that low byte 0x0c means clock enable, we need to
register a clock too. Do we need to extend this device specific section
to map a clock name, or is it acceptable for them to be nameless (ISTR
that the API will let you fetch a clock using devm_clock_get(dev, NULL);)

2. Given only 0x0b pin is actually a regulator and it's controlling
multiple devices, my plan when we got round to adding the VCM / EEPROM
support was simply to extend those mapping tables so that those
supplementary devices were also able to get that regulator...and the two
would share it. I think, from reading the regulator code and
documentation, that that's all fine - and it won't actually be disabled
until both drivers disable it. Does that sound about right?