Re: Help writing a custom HID driver

[Jose Diez <jose@mediacru.sh>]

Okay, so I've solved the watchdog issue, and now I want the driver to be 
loaded automatically. I've copied the module to /lib/modules/<kernel>/ 
and run depmod -a, and I can see it in modules.alias, but it looks like 
hid_generic grabs it first upon boot - my module is loaded correctly, 
but it doesn't grab the HID device.

If I `modprobe -r hid_generic` and then load my module, everything works 
correctly.
On 06/11/14 19:28, Jose Diez wrote:
> Thanks Benjamin. That fixed the issue. Have a great day.
>
> On 06/11/14 18:57, Benjamin Tissoires wrote:
>> Hi Jose,
>>
>> On Thu, Nov 6, 2014 at 1:33 PM, Jose Diez <jose@mediacru.sh> wrote:
>>> Hello linux-input,
>>>
>>> I'm trying to write a custom HID driver. It works fine, and I can send
>>> reports just fine, but one of the requirements of this device is 
>>> that I have
>>> to reply to reports with code 62 with another report with code 62, 
>>> which
>>> resets a watchdog in the device.
>>>
>>> This is my code so far: http://codepad.org/m4QiWhDt
>>>
>>> The problem is in line 40. It seems like I'm not allowed to call
>>> hid_hw_output_report from the raw_event callback handler. I've tried
>>> surrounding the call with spin_locks, but I still get the 
>>> "scheduling while
>>> atomic" error.
>> Yeah, when you are in the .event callback, you are basically called by
>> an IRQ, so you can not schedule a potentially blocking operation.
>>
>>> I'm not sure how to approach this - can someone help? It would be much
>>> appreciated. Thanks.
>> I would use a worker to do what you are trying to do. You can have a
>> look at the reset_worker we have in drivers/hid/hid-rmi.c.
>> When the event is not one we expected, we schedule a worker thread
>> which then sends an output report to the device. This way, the
>> blocking operation is sent from a different thread than the IRQ one.
>> It is kind of what you are willing to do.
>> There are many other examples of workers in the hid subtree, or you
>> can refer to the doc to find out more.
>>
>> Cheers,
>> Benjamin
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