linux-kernel - Re: [PATCH 14/18] acpi: utils: Add function to fetch dependent acpi

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Date:   Tue, 1 Dec 2020 15:23:00 +0000
From:   Dan Scally <djrscally@...il.com>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc:     linux-kernel@...r.kernel.org, linux-acpi@...r.kernel.org,
        linux-gpio@...r.kernel.org, linux-i2c@...r.kernel.org,
        linux-media@...r.kernel.org, devel@...ica.org, rjw@...ysocki.net,
        lenb@...nel.org, gregkh@...uxfoundation.org,
        mika.westerberg@...ux.intel.com, linus.walleij@...aro.org,
        bgolaszewski@...libre.com, wsa@...nel.org, yong.zhi@...el.com,
        sakari.ailus@...ux.intel.com, bingbu.cao@...el.com,
        tian.shu.qiu@...el.com, mchehab@...nel.org, robert.moore@...el.com,
        erik.kaneda@...el.com, pmladek@...e.com, rostedt@...dmis.org,
        sergey.senozhatsky@...il.com, linux@...musvillemoes.dk,
        kieran.bingham+renesas@...asonboard.com, jacopo+renesas@...ndi.org,
        laurent.pinchart+renesas@...asonboard.com,
        jorhand@...ux.microsoft.com, kitakar@...il.com,
        heikki.krogerus@...ux.intel.com
Subject: Re: [PATCH 14/18] acpi: utils: Add function to fetch dependent
 acpi_devices


On 01/12/2020 15:10, Andy Shevchenko wrote:
> On Mon, Nov 30, 2020 at 11:54:44PM +0000, Dan Scally wrote:
>> Hi Andy
>>
>> On 30/11/2020 18:23, Andy Shevchenko wrote:
>>> On Mon, Nov 30, 2020 at 01:31:25PM +0000, Daniel Scally wrote:
>>>> ACPI devices declare themselves dependent on other devices via the _DEP
>>>> buffer. Fetching the dependee from dependent is a matter of parsing
>>>> _DEP, but currently there's no method to fetch dependent from dependee.
>>>> Add one, so we can parse sensors dependent on a PMIC from the PMIC's
>>>> acpi_driver.
>>> Do I understand correctly that it's an existing table provided by firmware that
>>> (ab)uses _DEP in such way? Note, the specification doesn't tell we may use it
>>> in this way, OTOH I don't remember if it strictly forbids such use.
>>>
>>> So, please elaborate in the commit message why you need this and pint out to
>>> the 6.5.8 "_DEP (Operation Region Dependencies)" which clearly says about
>>> OpRegions and that part already supported by ACPI in the Linux, if I'm not
>>> mistaken, need to refresh my memory.
>>
>> Laurent's reply is good explanation, but for example see my Lenovo Miix
>> 510's DSDT:
>>
>>
>> https://gist.githubusercontent.com/djrscally/e64d112180517352fa3392878b0f4a7d/raw/88b90b3ea4204fd7845257b6666fdade47cc2981/dsdt.dsl
>>
>>
>> Search OVTI2680 and OVTI5648 for the cameras. Both are dependent on
>> IN3472 devices (PMI0 and PMI1) which are the discrete type that we're
>> attempting to handle here.
> Yes, it seems since PMIC is kinda "power resource" (don't mix with real power
> resource as by ACPI specifications) and that's why they decided to include it
> into _DEP.  So, it seems a de facto common practice. Thus, it would be nice to
> have the above in the commit message in some form. Can you do it?
>
Sure, no problem. I'll include that in the next version