linux-kernel - Re: [RFC PATCH v3 9/9] ipu3-cio2: Add functionality allowing software_node connections to sensors on platforms designed for Windows

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Message-ID: <CAHp75Vc9uYVvhBe3OyCJzCsU0EY9yi62hsxt3pAwppSfjB+jDg@mail.gmail.com>
Date:   Thu, 29 Oct 2020 22:26:56 +0200
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Laurent Pinchart <laurent.pinchart@...asonboard.com>
Cc:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Dan Scally <djrscally@...il.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux Media Mailing List <linux-media@...r.kernel.org>,
        Linus Walleij <linus.walleij@...aro.org>,
        prabhakar.mahadev-lad.rj@...renesas.com,
        "Krogerus, Heikki" <heikki.krogerus@...ux.intel.com>,
        Dmitry Torokhov <dmitry.torokhov@...il.com>,
        laurent.pinchart+renesas@...asonboard.com,
        kieran.bingham+renesas@...asonboard.com,
        Jacopo Mondi <jacopo+renesas@...ndi.org>,
        Rob Herring <robh@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Petr Mladek <pmladek@...e.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Tian Shu Qiu <tian.shu.qiu@...el.com>,
        Bingbu Cao <bingbu.cao@...el.com>,
        Sakari Ailus <sakari.ailus@...ux.intel.com>,
        Yong Zhi <yong.zhi@...el.com>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Tsuchiya Yuto <kitakar@...il.com>
Subject: Re: [RFC PATCH v3 9/9] ipu3-cio2: Add functionality allowing
 software_node connections to sensors on platforms designed for Windows

On Thu, Oct 29, 2020 at 10:21 PM Laurent Pinchart
<laurent.pinchart@...asonboard.com> wrote:
> On Mon, Oct 26, 2020 at 06:10:50PM +0200, Andy Shevchenko wrote:
> > On Sat, Oct 24, 2020 at 12:37:02PM +0300, Laurent Pinchart wrote:
> > > On Sat, Oct 24, 2020 at 09:50:07AM +0100, Dan Scally wrote:
> > > > On 24/10/2020 02:24, Laurent Pinchart wrote:
> > > > > On Mon, Oct 19, 2020 at 11:59:03PM +0100, Daniel Scally wrote:
> >
> > > > >> +              adev = acpi_dev_get_first_match_dev(supported_devices[i], NULL, -1);
> > > > >
> > > > > What if there are multiple sensor of the same model ?
> > > >
> > > > Hmm, yeah, that would be a bit of a pickle. I guess the newer
> > > > smartphones have multiple sensors on the back, which I presume are the
> > > > same model. So that will probably crop up at some point. How about
> > > > instead I use bus_for_each_dev() and in the applied function check if
> > > > the _HID is in the supported list?
> > >
> > > Sounds good to me.
> > >
> > > > >> +              if (!adev)
> > > > >> +                      continue;
> >
> > Please, don't.
> >
> > If we have so weird ACPI tables it must be w/a differently. The all, even badly
> > formed, ACPI tables I have seen so far are using _UID to distinguish instance
> > of the device (see second parameter to the above function).
> >
> > If we meet the very broken table I would like rather to know about, then
> > silently think ahead what could be best.
> >
> > I.o.w. don't change this until we will have a real example of the problematic
> > firmware.
>
> I'm not sure to follow you. Daniel's current code loops over all the
> supported HID (as stored in the supported_devices table), and then gets
> the first ACPI device for each of them. If multiple ACPI devices exist
> with the same HID, we need to handle them all, so enumerating all ACPI
> devices and checking whether their HID is one we handle seems to be the
> right option to me.

Devices with the same HID should be still different by another
parameter in ACPI. The above mentioned call just uses the rough
estimation for relaxed conditions. If you expect more than one device
with the same HID how do you expect to distinguish them? The correct
way is to use _UID. It may be absent, or set to a value. And this
value should be unique (as per U letter in UID abbreviation). That
said, the above is good enough till we find the firmware with the
above true (several devices with the same HID). Until then the code is
fine.


-- 
With Best Regards,
Andy Shevchenko