linux-kernel - Re: Question about using new request_threaded

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Message-ID: <20121217083759.0cbed418@lwn.net>
Date:	Mon, 17 Dec 2012 08:37:59 -0700
From:	Jonathan Corbet <corbet@....net>
To:	Marcos Lois Bermúdez <marcos.discalis@...il.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: Question about using new request_threaded_irq

On Mon, 17 Dec 2012 16:11:22 +0100
Marcos Lois Bermúdez <marcos.discalis@...il.com> wrote:

> For my understand if i call for example:
> 
> request_threaded_irq(irqmum, NULL, irq_handle, IRQF_TRIGGER_FALLING, 
> DEVICE_NAME, priv);
> 
> This seem to make a old Hard IRQ handler, and inside of this handler 
> sleep APIs can't be used, but i see some SPI drivers that seem to 
> register a IRQ of this form and make API calls that can sleep in the 
> handler.

Not quite.  The prototype for request_threaded_irq() is:

int request_threaded_irq(unsigned int irq, irq_handler_t handler,
			 irq_handler_t thread_fn, unsigned long irqflags,
			 const char *devname, void *dev_id)

Note the presents of *two* handlers, called "handler" and "thread_fn".
The first, "handler", is called in interrupt context; it's job is usually
to quiet the device and return; it cannot sleep.  If it's return value is
IRQ_WAKE_THREAD, the thread_fn() will be called in process context; it
*can* sleep.  In the example you cite, there is no immediate handler, only
the thread_fn(); the call to a blocking function from within the
thread_fn() is correct.

Hope that helps,

jon

Jonathan Corbet / LWN.net / corbet@....net
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