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From:   "Rafael J. Wysocki" <rafael@kernel.org>
Date:   Thu, 21 Jan 2021 15:39:55 +0100
Message-ID: <CAJZ5v0jO9O1zhBMNRNB5kRt1o86BTjr1kRuFUe=nNVTDwBQhEg@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 Thu, Jan 21, 2021 at 1:04 PM Daniel Scally <djrscally@gmail.com> wrote:
>
>
> On 21/01/2021 11:58, Rafael J. Wysocki wrote:
> > On Thu, Jan 21, 2021 at 10:47 AM Daniel Scally <djrscally@gmail.com> wrote:
> >> Hi Rafael
> >>
> >> On 19/01/2021 13:15, Rafael J. Wysocki wrote:
> >>> 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.
> >>
> >> This does work; do you prefer it in scan.c, or in utils.c (in which case
> >> with acpi_dep_list declared as external var in internal.h)?
> > Let's put it in scan.c for now, because there is the lock protecting
> > the list in there too.
> >
> > How do you want to implement this?  Something like "walk the list and
> > run a callback for the matching entries" or do you have something else
> > in mind?
>
>
> Something like this (though with a mutex_lock()). It could be simplified
> by dropping the prev stuff, but we have seen INT3472 devices with
> multiple sensors declaring themselves dependent on the same device
>
>
> struct acpi_device *
> acpi_dev_get_next_dependent_dev(struct acpi_device *supplier,
>                 struct acpi_device *prev)
> {
>     struct acpi_dep_data *dep;
>     struct acpi_device *adev;
>     int ret;
>
>     if (!supplier)
>         return ERR_PTR(-EINVAL);
>
>     if (prev) {
>         /*
>          * We need to find the previous device in the list, so we know
>          * where to start iterating from.
>          */
>         list_for_each_entry(dep, &acpi_dep_list, node)
>             if (dep->consumer == prev->handle &&
>                 dep->supplier == supplier->handle)
>                 break;
>
>         dep = list_next_entry(dep, node);
>     } else {
>         dep = list_first_entry(&acpi_dep_list, struct acpi_dep_data,
>                        node);
>     }
>
>
>     list_for_each_entry_from(dep, &acpi_dep_list, node) {
>         if (dep->supplier == supplier->handle) {
>             ret = acpi_bus_get_device(dep->consumer, &adev);
>             if (ret)
>                 return ERR_PTR(ret);
>
>             return adev;
>         }
>     }
>
>     return NULL;
> }

That would work I think, but would it be practical to modify
acpi_walk_dep_device_list() so that it runs a callback for every
consumer found instead of or in addition to the "delete from the list
and free the entry" operation?