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

[Heiner Kallweit <hkallweit1@gmail.com>]

On 11.11.2019 00:07, Tod E. Kurt wrote:
> Hi Heiner,
> 
> Yes, that was what I was starting from. I was hoping there was now an in-situ way of replacing kernel modules without a full kernel recompile.
> 
> I have tried this patch on Raspian 4.19.81 and Ubuntu 19 kernel 5.0.0-32 with no config changes.  I believe it solves the main issue.  However, I'm seeing another problem that I can't explain.
> 
> Specifically:
> - On reboot, device shows up in /sys/class/hidraw/
> - Opening with hidapi and (mis)using hidapi functions works, but,
> - Device is then removed from /sys/class/hidraw/
> 
> Under what circumstances can a device be removed from /sys/class/hidraw? 
> 
> If you'd like to trigger this yourself, run "blink1-tool --list" and see the blink(1) disappear. And yet "blink1-tool" can subsequently still communicate with the blink(1). Which I don't quite understand yet either.
> 
Once a dedicated device driver (like hid-led) is loaded, the raw device disappears.

I compiled blink1-tool on latest linux-next with the hid quirk patch I sent, but the blink(1) never disappears.
According to strace the tool doesn't use the /sys/class/hidraw interface but a low-level USB
interface via libusb.

> Cheers,
> -=Tod
> 
>> On Nov 10, 2019, at 9:25 a, Heiner Kallweit <hkallweit1@gmail.com> wrote:
>>
>> 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
>>>
>>>
>>
> 
>