Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Subject: Re: [PATCH v2 2/7] acpi: utils: Add function to fetch dependent
 acpi_devices
To:     "Rafael J. Wysocki" <rafael@kernel.org>
Cc:     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>
References: <20210118003428.568892-1-djrscally@gmail.com>
 <20210118003428.568892-3-djrscally@gmail.com>
 <CAJZ5v0gVQsZ4rxXW8uMidW9zfY_S50zpfrL-Gq0J3Z4-qqBiww@mail.gmail.com>
 <b381b48e-1bf2-f3e7-10a6-e51cd261f43c@gmail.com>
 <CAJZ5v0iU2m4Hs6APuauQ645DwbjYaB8nJFjYH0+7yQnR-FPZBQ@mail.gmail.com>
 <e2d7e5e9-920f-7227-76a6-b166e30e11e5@gmail.com>
 <CAJZ5v0gg5oXG3yOO9iDvPKSsadYrFojW6JcKfZcQbFFpO78zAQ@mail.gmail.com>
 <85ccf00d-7c04-b1da-a4bc-82c805df69c9@gmail.com>
 <CAJZ5v0jO9O1zhBMNRNB5kRt1o86BTjr1kRuFUe=nNVTDwBQhEg@mail.gmail.com>
 <0fac24d2-e8fc-7dc8-0f2f-44c7aadb1daf@gmail.com>
 <CAJZ5v0jVxMMGh6k-vXeBRsCtD0L14poNUrg4kZOpCfOz2sZGZQ@mail.gmail.com>
From:   Daniel Scally <djrscally@gmail.com>
Message-ID: <ee8f6b58-55c8-e0a0-c161-bdef361f9e0a@gmail.com>
Date:   Thu, 21 Jan 2021 21:06:05 +0000
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101
 Thunderbird/68.10.0
MIME-Version: 1.0
In-Reply-To: <CAJZ5v0jVxMMGh6k-vXeBRsCtD0L14poNUrg4kZOpCfOz2sZGZQ@mail.gmail.com>
Content-Type: text/plain; charset=utf-8
Content-Transfer-Encoding: 8bit
Content-Language: en-US
Precedence: bulk


On 21/01/2021 18:08, Rafael J. Wysocki wrote:
> On Thu, Jan 21, 2021 at 5:34 PM Daniel Scally <djrscally@gmail.com> wrote:
>>
>> On 21/01/2021 14:39, Rafael J. Wysocki wrote:
>>> 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?
>>
>> 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

Well it my case it's more to return a pointer to the dep->consumer's
acpi_device for a matching entry, so my idea was where there's multiple
dependents you could use this as an iterator...but it could just be
extended to that if needed later; I don't actually need to do it right now.


> 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

No problem;  I'll tweak that then

>> 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.


Yeah that's what I mean by helper; I'll do that then; thanks