Re: Linux "hid_led" vs "hidraw" USB HID question

[Heiner Kallweit <hkallweit1@gmail.com>]

On 10.11.2019 17:59, Tod E. Kurt wrote:
> Hi Heiner, (and others on the list)
> 
> Thanks for your quick and detailed response. 
> 
> I am endeavoring to try the patch out now.  But I've not built a desktop Linux kernel or kernel modules in about 15 years.  Do you have a preferred recipe for applying this patch to an existing distro?  Since 'hid-quirks' isn't a module, this means recompiling the entire HID driver, correct?  I mostly test against various modern Ubuntu or Raspian flavors of Debian, if that matters.
> 
See e.g. here: https://wiki.ubuntu.com/Kernel/BuildYourOwnKernel

> Also, is there a mitigation for users running production distros that doesn't involve a recompile? 
> 
I don't think so (at least from kernel perspective). What you could do is adding an integration with
the /sys/class/led interface in your library (if it should be suitable for your use cases) and
auto-detect which interface to use.

> Thanks,
> -=Tod
> 
Heiner

>> On Nov 10, 2019, at 2:44 a, Heiner Kallweit <hkallweit1@gmail.com> wrote:
>>
>> On 10.11.2019 04:26, Tod E. Kurt wrote:
>>> HiI
>>>
>> Hi Tod,
>>
>>> Since you are listed as author of "hid-led.c": 
>>>   https://github.com/torvalds/linux/blob/master/drivers/hid/hid-led.c, 
>>> I was wondering if you could offer some insight on an issue I'm seeing.
>>> I'm a maintainer of "hidapi" and "node-hid", cross-platform C and NodeJs libraries for accessing HID devices, and I'm the creator of the ThingM blink(1) USB LED that "hid-led" controls.
>>>
>>> On the distros I've seen (Ubuntu, Raspian) where "hid-led" is enabled, when inserting a blink(1) device, the "hid-led" driver appears to grab the device and remove it from available "hidraw" devices.  This makes generic hidraw-based systems (like "hidapi" and the upcoming Chrome WebHID) unable to see the blink(1)
>>>
>>> I have tried blacklisting the "hid-led" module but the problem persist. Ffrom dmesg and lsmod the module does appear to not be loaded on reboot.
>>>
>>> Any insights on what's going on?  Any tips on how to debug this or how to prevent this from occurring?
>>>
>> When hid-led was written it was needed to add the LED devices to hid_have_special_driver list.
>> Else the driver can't take control over the device. Side effect is that even if hid-led
>> isn't loaded hid-generic can't take control.
>> I think since e04a0442d33b ("HID: core: remove the absolute need of hid_have_special_driver[]")
>> it's no longer needed to have the LED devices in hid_have_special_driver.
>> Could you please test the following patch? If hid-led is loaded is should control the
>> device, if it's blacklisted hid-generic should have the control.
>>
>>
>> diff --git a/drivers/hid/hid-quirks.c b/drivers/hid/hid-quirks.c
>> index c50bcd967..bdaab79f7 100644
>> --- a/drivers/hid/hid-quirks.c
>> +++ b/drivers/hid/hid-quirks.c
>> @@ -419,13 +419,6 @@ static const struct hid_device_id hid_have_special_driver[] = {
>> #if IS_ENABLED(CONFIG_HID_LCPOWER)
>> 	{ HID_USB_DEVICE(USB_VENDOR_ID_LCPOWER, USB_DEVICE_ID_LCPOWER_LC1000) },
>> #endif
>> -#if IS_ENABLED(CONFIG_HID_LED)
>> -	{ HID_USB_DEVICE(USB_VENDOR_ID_DREAM_CHEEKY, USB_DEVICE_ID_DREAM_CHEEKY_WN) },
>> -	{ HID_USB_DEVICE(USB_VENDOR_ID_DREAM_CHEEKY, USB_DEVICE_ID_DREAM_CHEEKY_FA) },
>> -	{ HID_USB_DEVICE(USB_VENDOR_ID_MICROCHIP, USB_DEVICE_ID_LUXAFOR) },
>> -	{ HID_USB_DEVICE(USB_VENDOR_ID_RISO_KAGAKU, USB_DEVICE_ID_RI_KA_WEBMAIL) },
>> -	{ HID_USB_DEVICE(USB_VENDOR_ID_THINGM, USB_DEVICE_ID_BLINK1) },
>> -#endif
>> #if IS_ENABLED(CONFIG_HID_LENOVO)
>> 	{ HID_USB_DEVICE(USB_VENDOR_ID_LENOVO, USB_DEVICE_ID_LENOVO_TPKBD) },
>> 	{ HID_USB_DEVICE(USB_VENDOR_ID_LENOVO, USB_DEVICE_ID_LENOVO_CUSBKBD) },
>> -- 
>> 2.24.0
>>
>>> I can send you blink(1) devices and "hidapi" test programs if you'd like to try to replicate this.
>>>
>> Thanks for the offer, I've got a blink(1) already. Just tested the patch with this device
>> and it worked properly like described above.
>>
>>> Thanks!
>>> -=Tod
>>
>> Heiner
> 
>