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From: Heiner Kallweit <>
To: "Tod E. Kurt" <>
Cc: "open list:HID CORE LAYER" <>,
	Linux USB Mailing List <>
Subject: Re: Linux "hid_led" vs "hidraw" USB HID question
Date: Sun, 10 Nov 2019 11:44:31 +0100
Message-ID: <> (raw)
In-Reply-To: <>

On 10.11.2019 04:26, Tod E. Kurt wrote:
> HiI
Hi Tod,

> Since you are listed as author of "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[] = {

> 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


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Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <>
2019-11-10 10:44 ` Heiner Kallweit [this message]
2019-11-10 16:59   ` Tod E. Kurt
2019-11-10 17:25     ` Heiner Kallweit
2019-11-10 23:07       ` Tod E. Kurt
2019-11-11 21:31         ` Heiner Kallweit

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