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

["Tod E. Kurt" <tod@todbot.com>]

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.

Also, is there a mitigation for users running production distros that doesn't involve a recompile? 

Thanks,
-=Tod

> 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