Re: [PATCH v8 3/4] gpiolib: add irq_not_threaded flag to gpio_chip

[Alexandre Courbot <gnurou@xxxxxxxxx>]

On Mon, Oct 20, 2014 at 7:19 PM, Octavian Purdila
<octavian.purdila@xxxxxxxxx> wrote:
> On Mon, Oct 20, 2014 at 8:08 AM, Alexandre Courbot <gnurou@xxxxxxxxx> wrote:
>>
>> On Wed, Oct 15, 2014 at 11:48 PM, Octavian Purdila
>> <octavian.purdila@xxxxxxxxx> wrote:
>> > Some GPIO chips (e.g. the DLN2 USB adapter) have blocking get/set
>> > operation but do not need a threaded irq handler.
>>
>> Sorry if you already explained this (I have been a little bit late
>> with the GPIO reviews recently), but does this optimization bring a
>> significant benefit that justifies adding another field in struct
>> gpio_chip? If so it would be nice to have it in the commit message. If
>> not, do we need this at all?
>
> Hi Alexandre,
>
> In the case DLN2 USB GPIO adapter the GPIO interrupt is generated in
> the completion routine of a receive URB, which means that we are in
> interrupt context. If a threaded irq is used, we would have to
> schedule work instead of running to interrupt handler directly which
> is unnecessary and adds latency.
>
> BTW, AFAIC Linus W already merged this patch in his next tree, I am
> keeping it in this series because it was not pulled in the mfd-next
> tree.

You're right, it's all good then. Thanks for the explanation.
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