Date:   Thu, 21 Jan 2021 19:08:31 +0100
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Daniel Scally <djrscally@...il.com>
Cc:     "Rafael J. Wysocki" <rafael@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
        linux-gpio@...r.kernel.org, linux-i2c <linux-i2c@...r.kernel.org>,
        Platform Driver <platform-driver-x86@...r.kernel.org>,
        "open list:ACPI COMPONENT ARCHITECTURE (ACPICA)" <devel@...ica.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Len Brown <lenb@...nel.org>, andy@...nel.org,
        Mika Westerberg <mika.westerberg@...ux.intel.com>,
        Linus Walleij <linus.walleij@...aro.org>,
        Bartosz Golaszewski <bgolaszewski@...libre.com>,
        Wolfram Sang <wsa@...nel.org>,
        Lee Jones <lee.jones@...aro.org>,
        Hans de Goede <hdegoede@...hat.com>,
        Mark Gross <mgross@...ux.intel.com>,
        Robert Moore <robert.moore@...el.com>,
        Erik Kaneda <erik.kaneda@...el.com>,
        Sakari Ailus <sakari.ailus@...ux.intel.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Kieran Bingham <kieran.bingham@...asonboard.com>
Subject: Re: [PATCH v2 2/7] acpi: utils: Add function to fetch dependent acpi_devices

On Thu, Jan 21, 2021 at 5:34 PM Daniel Scally <djrscally@...il.com> wrote:
>
>
> On 21/01/2021 14:39, Rafael J. Wysocki wrote:
> > On Thu, Jan 21, 2021 at 1:04 PM Daniel Scally <djrscally@...il.com> wrote:
> >>
> >> On 21/01/2021 11:58, Rafael J. Wysocki wrote:
> >>> On Thu, Jan 21, 2021 at 10:47 AM Daniel Scally <djrscally@...il.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@...il.com> wrote:
> >>>>>> On 18/01/2021 16:14, Rafael J. Wysocki wrote:
> >>>>>>> On Mon, Jan 18, 2021 at 1:37 AM Daniel Scally <djrscally@...il.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?
>
>
> I think that this would work fine, if that's the way you want to go.
> We'd just need to move everything inside the if (dep->supplier ==
> handle) block to a new callback, and for my purposes I think also add a
> way to stop parsing the list from the callback (so like have the
> callbacks return int and stop parsing on a non-zero return). Do you want
> to expose that ability to pass a callback outside of ACPI?

Yes.

> Or just export helpers to call each of the callbacks (one to fetch the next
> dependent device, one to decrement the unmet dependencies counter)

If you can run a callback for every matching entry, you don't really
need to have a callback to return the next matching entry.  You can do
stuff for all of them in one go (note that it probably is not a good
idea to run the callback under the lock, so the for loop currently in
there is not really suitable for that).

> Otherwise, I'd just need to update the 5 users of that function either
> to use the new helper or else to also pass the decrement dependencies
> callback.

Or have a wrapper around it passing the decrement dependencies
callback for the "typical" users.

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