Re: Help writing a custom HID driver

[Jose Diez <jose@mediacru.sh>]

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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