linux-kernel - Re: [PATCH RESEND v6] platform: x86: Add ChromeOS ACPI device driver

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Date:   Thu, 14 Apr 2022 14:07:30 +0500
From:   Muhammad Usama Anjum <usama.anjum@...labora.com>
To:     Hans de Goede <hdegoede@...hat.com>,
        "Rafael J. Wysocki" <rafael@...nel.org>
Cc:     usama.anjum@...labora.com, Len Brown <lenb@...nel.org>,
        Mark Gross <markgross@...nel.org>,
        Collabora Kernel ML <kernel@...labora.com>,
        Guenter Roeck <groeck@...omium.org>,
        Benson Leung <bleung@...omium.org>,
        Dmitry Torokhov <dtor@...omium.org>,
        Gwendal Grignou <gwendal@...omium.org>, vbendeb@...omium.org,
        Andy Shevchenko <andy@...radead.org>,
        Ayman Bagabas <ayman.bagabas@...il.com>,
        Benjamin Tissoires <benjamin.tissoires@...hat.com>,
        Blaž Hrastnik <blaz@...n.io>,
        Darren Hart <dvhart@...radead.org>,
        Dmitry Torokhov <dmitry.torokhov@...il.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jeremy Soller <jeremy@...tem76.com>,
        Mattias Jacobsson <2pi@....nu>,
        Mauro Carvalho Chehab <mchehab+samsung@...nel.org>,
        Rajat Jain <rajatja@...gle.com>,
        Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
        Platform Driver <platform-driver-x86@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
        "Rafael J . Wysocki" <rafael.j.wysocki@...el.com>,
        Enric Balletbo i Serra <eballetbo@...il.com>
Subject: Re: [PATCH RESEND v6] platform: x86: Add ChromeOS ACPI device driver

On 4/11/22 6:40 PM, Hans de Goede wrote:
> Hi,
> 
> On 4/11/22 15:37, Rafael J. Wysocki wrote:
>> On Mon, Apr 11, 2022 at 3:26 PM Hans de Goede <hdegoede@...hat.com> wrote:
>>>
>>> Hi,
>>>
>>> On 4/7/22 14:35, Muhammad Usama Anjum wrote:
>>>> From: Enric Balletbo i Serra <enric.balletbo@...labora.com>
>>>>
>>>> The x86 Chromebooks have ChromeOS ACPI device. This driver attaches to
>>>> the ChromeOS ACPI device and exports the values reported by ACPI in a
>>>> sysfs directory. This data isn't present in ACPI tables when read
>>>> through ACPI tools, hence a driver is needed to do it. The driver gets
>>>> data from firmware using ACPI component of the kernel. The ACPI values
>>>> are presented in string form (numbers as decimal values) or binary
>>>> blobs, and can be accessed as the contents of the appropriate read only
>>>> files in the standard ACPI device's sysfs directory tree. This data is
>>>> consumed by the ChromeOS user space.
>>>>
>>>> Cc: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
>>>> Cc: Dmitry Torokhov <dmitry.torokhov@...il.com>
>>>> Signed-off-by: Enric Balletbo i Serra <enric.balletbo@...labora.com>
>>>> Signed-off-by: Muhammad Usama Anjum <usama.anjum@...labora.com>
>>>
>>>
>>> Thanks overall this looks pretty good to me.  The only remark which
>>> I have is that I would like to see the Kconfig symbol changed
>>> from CONFIG_ACPI_CHROMEOS to CONFIG_CHROMEOS_ACPI to match the
>>> filename.
>>>

I'll rename in next version.

>>> CONFIG_ACPI_CHROMEOS to me suggests that this is an ACPI subsystem
>>> Kconfig option which, with the driver living under
>>> drivers/platform/x86 it is not.
>>>
>>> There is no need to send a new version for this, if you agree
>>> with the change let me know and I can change this while merging
>>> the driver.
>>>
>>> Rafael, before I merge this do you have any (more) remarks
>>> about this driver?
>>
>> I'm not sure why it has to be an acpi_driver.
>>
>> I think that the generic enumeration code creates a platform device
>> for this ACPI device object, so why can't it bind to that platform
>> device?
>>
>> Generally speaking, IMV we should avoid adding drivers binding
>> directly to ACPI device objects, because that is confusing (it is kind
>> of like binding directly to an of_node) and it should be entirely
>> avoidable.
> 
> Ah I missed that, good point.
> 
> Muhammad can you give turning this into a platform driver a try please?
> 
> Note this will change all the sysfs attribute paths from:
> 
> /sys/bus/acpi/devices/GGL0001:00/...
> 
> to:
> 
> /sys/bus/platform/devices/GGL0001:00/...
> 
> and the ABI documentation should be updated accordingly.
> 

Thank you for comments and directions. They mean a lot. I'll make the
changes in next version.

> Regards,
> 
> Hans
> 
> 
> 

-- 
Muhammad Usama Anjum