Message-ID: <3690C9ED-FC73-4783-8EB4-2CFA148E8573@gmail.com>
Date: Thu, 10 Jul 2025 08:15:49 -0700
From: "Derek J. Clark" <derekjohn.clark@...il.com>
To: Benjamin Tissoires <bentiss@...nel.org>
CC: Jiri Kosina <jikos@...nel.org>, Mario Limonciello <superm1@...nel.org>,
 Xino Ni <nijs1@...ovo.com>, Zhixin Zhang <zhangzx36@...ovo.com>,
 Mia Shao <shaohz1@...ovo.com>, Mark Pearson <mpearson-lenovo@...ebb.ca>,
 "Pierre-Loup A . Griffais" <pgriffais@...vesoftware.com>,
 linux-input@...r.kernel.org, linux-doc@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/6] HID: Add Legion Go S Driver



On July 3, 2025 6:48:00 AM PDT, Benjamin Tissoires <bentiss@...nel.org> wrote:
>Hi Derek,
>
>[I'll answer to this email with a very high level overview of it, as I'm
>not sure I'll have time to dig much deeper in 6/6 today.]
>
>On Jul 02 2025, Derek J. Clark wrote:
>> This series adds initial support for the Legion Go S's built-in
>> controller HID configuration interface. In the first patch a new HID
>> uevent property is added, HID_FIRMWARE_VERSION, so as to permit fwupd
>> to read the firmware version of the HID interface without detaching the
>> kernel driver.
>
>That immediately raise red flags on my side. HID_FIRMWARE_VERSION will
>likely be used only for this new driver, and that means a special case
>in each and every client.
>
>We had to deal with firmware versions in the past in the HID drivers,
>and we ended up relying on the uniq field of the hid_device (because the
>serial+firmware version uniquely identify the device).
>

>> The second patch adds the ability for an hid_driver to
>> assign new/arbitrary uevent properties for static data that doesn't
>> benefit from having a sysfs entry.
>
>That, in my mind, is even worse (for the reasons above).
>
Hi Benjamin,

Sorry abtthe late reply. Travel & holidays have me a bit behind.

I'll let Mario and Richard hash out the specifics on these points. I'll just add a bit of context to why they're in this series. Prior to this, the fwupd plugin would disconnect this driver to query this information to see if there was an available update. As this can be triggered by a system daemon during gameplay that's not a reasonable expectation. Originally we had these as sysfs entries, and returning to them, would be simple enough, but we felt like this is a fairly standard piece of information that should be available. I wasn't aware of the uniq property being used for this historically, but from an outside looking in perspective this seems a bit convoluted. Apart from just being unintuitive if you're not familiar, userspace is going to need bespoke ways to interpret this anyway as serial numbers and firmware formatting are not consistent between manufacturers.

I'll wait to adjust this until a more thorough discussion has taken place.

>> The third patch adds the VID and PID
>> for the Lenovo Legion Go S MCU. 
>
>Which shouldn't be in its own patch, but part of the driver initial
>patch.

I can do that. My reasoning was simply that if another patch becomes reliant on the VID and you needed to revert the other patches for any reason there would be a conflict.

>> The fourth patch adds ABI documentation
>> for the config interface introduced in the final patch. The fifth patch
>> introduces the core lenovo-legos-hid driver which acts as a routing
>> interface for the different endpoints. 
>
>That "core" patch is IMO useless. All it does is:
>- check for the USB endpoint (but in the wrong way, because if you
>	insert a device through uhid with the same PID/VID it will crash)
>- replace the HID-core core functions with the same code

Can you point me to a better way?

This series only implements the config endpoint. ATM the gamepad, touchpad, and IMU are combined into a single Steam Deck like interface in root level userspace as a uhid device. I do have some plans for how to do this in the kernel instead, but the proposal isn't ready yet so I need to keep the hidraw devices available to userspace that aren't implemented yet for backwards compatibility.

>Really, this should be squashed into the next patch (with 3/6 then).
>
>Also, why adding a new subdirectory? All the hid drivers are flat in the
>drivers/hid/ directory, and the subdirs are for transport layers. There
>is one exception for the surface driver but I don't see why you need
>such an exception (yeah, the code is big, but what's the difference in
>having a 1500 lines of code source in its own subdir vs at the root?)

Sure, I can change it to a single file if that's preferable in this subsystem. This is my first foray into kernel HID drivers so I'm not super familiar with the style preferences yet. Breaking everything up by logical subset made sense to me but I'm not married to it. There

>> The sixth path introduces the 
>> config lenovo-legos-hid driver wich uses both the HID_FIRMWARE_VERSION
>> as well as arbitrary uevent properties. Additional interfaces and config
>> properties are planned to be added in a future series.
>
>That one is too big for my liking. Generally speaking, a commit
>descrition which says "this does this and that" can be split into 2
>patches at least :)

I figured, but I wasn't sure how you'd prefer I break it up. I was thinking that one patch per attribute group would make sense but wanted some feedback before I did that to avoid going down the wrong path with them.

>What kind of future interfaces and config properties are you planning?

The MCU has a gamepad interface that is more complete than what the xpad driver uses, which includes some back paddles as well as native gyro data which is passed through from the IMU. There's also a separate IMU endpoint so there are a couple options how this can be used. My thoughts are that a sysfs attribute could toggle if gyro is added to one of the joysticks using the IMU data included in the gamepad report, and the external one could be exposed as a motion sensor with the same uniq. Then userspace can determine how to use it.

The touchpad works in both abs and rel modes with the default kernel implementations but additional functionality can be gained through Steam Input if this is integrated into the gamepad.

As far as additional attributes for the config interface, there is hardware level button remapping and calibration for all axes that need to be added but weren't considered critical for initial support from Lenovo.

>> 
>> Patch 6 introduces a checkpatch WARNING that I'm unable to resolve:
>> WARNING: ENOSYS means 'invalid syscall nr' and nothing else
>> 1292: FILE: drivers/hid/lenovo-legos-hid/lenovo-legos-hid-config.c:1085:
>> +       case -ENOSYS: /* during rmmod -ENOSYS is expected */
>
>We can losely waive those while merging. We do it quite often actually.
>
>But trying to minimize checkpatch warnings is a good thing, so thanks
>for that.

Cool, I'll keep a brief note for posterity. 

Thanks,
Derek

>> 
>> This error handling case was added as it is experienced in the real world
>> when the driver is rmmod. The LED subsystem produces this error code in
>> its legacy code and this is not a new novel use of -ENOSYS, we are simply
>> catching the case to avoid spurious errors in dmesg when the driver is
>> removed. If there is a way to prevent this error from being triggered by
>> checkpatch in the first place, that would be an ideal remedy, but I'm not
>> aware how that can be done at this time.
>
>Again, nothing to worry about.
>
>Cheers,
>Benjamin
>
>> 
>> Signed-off-by: Derek J. Clark <derekjohn.clark@...il.com>
>> 
>> 
>> Derek J. Clark (4):
>>   HID: Add Legion Go S ID's
>>   HID: Add documentation for lenovo-legos-hid driver
>>   HID: Add lenovo-legos-hid core
>>   HID: Add lenovo-legos-hid configuration endpoint interface
>> 
>> Mario Limonciello (2):
>>   HID: Include firmware version in the uevent
>>   HID: Allow HID drivers to add more uevent variables
>> 
>>  .../ABI/testing/sysfs-driver-lenovo-legos-hid |  269 +++
>>  MAINTAINERS                                   |    7 +
>>  drivers/hid/Kconfig                           |    2 +
>>  drivers/hid/Makefile                          |    2 +
>>  drivers/hid/hid-core.c                        |   11 +
>>  drivers/hid/hid-ids.h                         |    4 +
>>  drivers/hid/lenovo-legos-hid/Kconfig          |   11 +
>>  drivers/hid/lenovo-legos-hid/Makefile         |    6 +
>>  drivers/hid/lenovo-legos-hid/config.c         | 1518 +++++++++++++++++
>>  drivers/hid/lenovo-legos-hid/config.h         |   19 +
>>  drivers/hid/lenovo-legos-hid/core.c           |  122 ++
>>  drivers/hid/lenovo-legos-hid/core.h           |   25 +
>>  include/linux/hid.h                           |    2 +
>>  13 files changed, 1998 insertions(+)
>>  create mode 100644 Documentation/ABI/testing/sysfs-driver-lenovo-legos-hid
>>  create mode 100644 drivers/hid/lenovo-legos-hid/Kconfig
>>  create mode 100644 drivers/hid/lenovo-legos-hid/Makefile
>>  create mode 100644 drivers/hid/lenovo-legos-hid/config.c
>>  create mode 100644 drivers/hid/lenovo-legos-hid/config.h
>>  create mode 100644 drivers/hid/lenovo-legos-hid/core.c
>>  create mode 100644 drivers/hid/lenovo-legos-hid/core.h
>> 
>> -- 
>> 2.50.0
>> 

Powered by blists - more mailing lists