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From:   "Rafael J. Wysocki" <rafael@kernel.org>
Date:   Tue, 19 Jan 2021 14:15:21 +0100
Message-ID: <CAJZ5v0iU2m4Hs6APuauQ645DwbjYaB8nJFjYH0+7yQnR-FPZBQ@mail.gmail.com>
Subject: Re: [PATCH v2 2/7] acpi: utils: Add function to fetch dependent acpi_devices
To:     Daniel Scally <djrscally@gmail.com>
Cc:     "Rafael J. Wysocki" <rafael@kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        ACPI Devel Maling List <linux-acpi@vger.kernel.org>,
        linux-gpio@vger.kernel.org, linux-i2c <linux-i2c@vger.kernel.org>,
        Platform Driver <platform-driver-x86@vger.kernel.org>,
        "open list:ACPI COMPONENT ARCHITECTURE (ACPICA)" <devel@acpica.org>,
        "Rafael J. Wysocki" <rjw@rjwysocki.net>,
        Len Brown <lenb@kernel.org>, andy@kernel.org,
        Mika Westerberg <mika.westerberg@linux.intel.com>,
        Linus Walleij <linus.walleij@linaro.org>,
        Bartosz Golaszewski <bgolaszewski@baylibre.com>,
        Wolfram Sang <wsa@kernel.org>,
        Lee Jones <lee.jones@linaro.org>,
        Hans de Goede <hdegoede@redhat.com>,
        Mark Gross <mgross@linux.intel.com>,
        Robert Moore <robert.moore@intel.com>,
        Erik Kaneda <erik.kaneda@intel.com>,
        Sakari Ailus <sakari.ailus@linux.intel.com>,
        Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
        Laurent Pinchart <laurent.pinchart@ideasonboard.com>,
        Kieran Bingham <kieran.bingham@ideasonboard.com>
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On Mon, Jan 18, 2021 at 9:51 PM Daniel Scally <djrscally@gmail.com> wrote:
>
> On 18/01/2021 16:14, Rafael J. Wysocki wrote:
> > On Mon, Jan 18, 2021 at 1:37 AM Daniel Scally <djrscally@gmail.com> wrote:
> >> In some ACPI tables we encounter, devices use the _DEP method to assert
> >> a dependence on other ACPI devices as opposed to the OpRegions that the
> >> specification intends. We need to be able to find those devices "from"
> >> the dependee, so add a function to parse all ACPI Devices and check if
> >> the include the handle of the dependee device in their _DEP buffer.
> > What exactly do you need this for?
>
> So, in our DSDT we have devices with _HID INT3472, plus sensors which
> refer to those INT3472's in their _DEP method. The driver binds to the
> INT3472 device, we need to find the sensors dependent on them.
>

Well, this is an interesting concept. :-)

Why does _DEP need to be used for that?  Isn't there any other way to
look up the dependent sensors?

>
> > Would it be practical to look up the suppliers in acpi_dep_list instead?
> >
> > Note that supplier drivers may remove entries from there, but does
> > that matter for your use case?
>
> Ah - that may work, yes. Thank you, let me test that.

Even if that doesn't work right away, but it can be made work, I would
very much prefer that to the driver parsing _DEP for every device in
the namespace by itself.