linux-kernel - Re: [PATCH v2] platform/x86: add Gigabyte WMI temperature driver

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Date:   Fri, 9 Apr 2021 23:40:00 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Hans de Goede <hdegoede@...hat.com>,
        Thomas Weißschuh <linux@...ssschuh.net>
Cc:     platform-driver-x86@...r.kernel.org,
        Mark Gross <mgross@...ux.intel.com>,
        linux-kernel@...r.kernel.org,
        Barnabás Pőcze <pobrn@...tonmail.com>,
        Matthew Garrett <mjg59@...f.ucam.org>
Subject: Re: [PATCH v2] platform/x86: add Gigabyte WMI temperature driver

On 4/8/21 9:07 AM, Hans de Goede wrote:
> Hi Guenter,
> 
> On 4/8/21 5:08 PM, Guenter Roeck wrote:
>> On Mon, Apr 05, 2021 at 10:48:10PM +0200, Thomas Weißschuh wrote:
>>> Changes since v1:
>>> * Incorporate feedback from Barnabás Pőcze
>>>   * Use a WMI driver instead of a platform driver
>>>   * Let the kernel manage the driver lifecycle
>>>   * Fix errno/ACPI error confusion
>>>   * Fix resource cleanup
>>>   * Document reason for integer casting
>>>
>>> Thank you Barnabás for your review, it is much appreciated.
>>>
>>> -- >8 --
>>>
>>> Tested with a X570 I Aorus Pro Wifi.
>>> The mainboard contains an ITE IT8688E chip for management.
>>> This chips is also handled by drivers/hwmon/i87.c but as it is also used
>>> by the firmware itself it needs an ACPI driver.
>>>
>>> Unfortunately not all sensor registers are handled by the firmware and even
>>> less are exposed via WMI.
>>>
>>> Signed-off-by: Thomas Weißschuh <linux@...ssschuh.net>
>>> ---
>>>  drivers/platform/x86/Kconfig        |  11 +++
>>>  drivers/platform/x86/Makefile       |   1 +
>>>  drivers/platform/x86/gigabyte-wmi.c | 138 ++++++++++++++++++++++++++++
>>
>> Originally drivers/platform was supposed to be used for platform specific
>> code. Not that I have control over it, but I really dislike that more and
>> more hwmon drivers end up there.
>>
>> At least hwmon is in good company - I see drivers for various other subsystems
>> there as well. I just wonder if that is such a good idea. That entire directory
>> is bypassing subsystem maintainer reviews.
> 
> In case you are not aware I've recent(ish) taken over the drivers/platform/x86
> maintainership from Andy Shevchenko.
> 
> Yes it is a bit of an odd grab-bag it mostly deals with vendor specific
> ACPI / WMI interfaces which often more or less require using a single
> driver while offering multiple functionalities. These firmware interfaces
> do not really lend themselves to demultiplexing through something like
> MFD. These are mostly found on laptops where they deal with some or all of:
> 
> - Hotkeys for brightness adjust / wlan-on/off toggle, touchpad on/off toggle, etc.
>   (input subsystem stuff)
> - Mic. / Speaker mute LEDS (and other special LEDs) found on some laptops
>   (LED subsystem stuff)
> - Enabling/disabling radios
>   (rfkill stuff)
> - Controlling the DPTF performance profile
>   (ACPI stuff)
> - Various sensors, some hwmon, some IIO
> - Backlight control (drm/kms subsys)
> - Enabling/disabling of LCD-builtin privacy filters (requires KMS/DRM subsys integration, pending)
> - Fan control (hwmon subsys)
> 
> And often all of this in a single driver. This is all "stuff" for which
> there are no standard APIs shared between vendors, so it is a free for
> all and often it is all stuffed behind a single WMI or ACPI object,
> because that is how the vendor's drivers under Windows work.
> 
> It certainly is not my intention to bypass review by other subsystem
> maintainers and when there are significant questions I do try to always
> get other subsys maintainers involved. See e.g. this thread, but also the
> "[PATCH 1/3] thinkpad_acpi: add support for force_discharge" thread
> where I asked for input from sre for the power-supply aspects of that.
> 
> The WMI code was reworked a while back to make WMI be a bus and have
> individual WMI objects be devices on that bus. version 2 of this
> driver has been reworked to use this. Since this new driver is just a hwmon
> driver and as this is for a desktop I expect it will stay that way,
> I'm fine with moving this one over to drivers/hwmon if that has your
> preference.
> 
I thought about it, but I don't think it makes much sense since all other
WMI drivers are in drivers/platform.

> As for other cases then this driver, if you want to make sure you are at
> least Cc-ed on all hwmon related changes I'm fine with adding you as a
> reviewer to the pdx86 MAINTAINERS entry.
> 
I think I have a better idea: I'll add a regex pattern into the MAINTAINERS
entry for hardware monitoring drivers. This way we should get copied whenever
anyone adds a hardware monitoring driver into the tree.

Thanks,
Guenter