linux-kernel - Re: [PATCH 01/01] MFD: add ADC support to DA9052/53 MFD core v2

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Message-Id: <201202211204.45658.arnd@arndb.de>
Date:	Tue, 21 Feb 2012 12:04:45 +0000
From:	Arnd Bergmann <arnd@...db.de>
To:	Ashish Jangam <ashish.jangam@...tcummins.com>
Cc:	broonie@...nsource.wolfsonmicro.com, sameo@...ux.intel.com,
	linux-kernel@...r.kernel.org, dajun.chen@...semi.com
Subject: Re: [PATCH 01/01] MFD: add ADC support to DA9052/53 MFD  core v2

On Tuesday 21 February 2012, Ashish Jangam wrote:
> > On Mon, Feb 20, 2012 at 12:07:27PM +0000, Arnd Bergmann wrote:
> > 
> > > Also, I would recommend using request_irq instead of 
> > > request_threaded_irq here because the function only has a single 
> > > "complete()" call in it, just like a threaded IRQ handler has. There 
> > > is no point going through another thread just to wake up the one that is blocked.
> > 
> > Actually in this case that won't work as the interrupt is generated by the chip interrupt controller and as the chip is I2C/SPI controlled it is itself threaded and can only generate threaded interrupts as genirq can't get back into hard interrupt context.
> > 
> > As a result of this restriction when an interrupt handler doesn't care what context it runs in it's better to use request_any_context_irq().
> > This will do a normal IRQ when it can but will bind successfully to a threaded IRQ if that's what's provided.
> 
> as threaded IRQs are only being used, request_any_context_irq() will
> internally call request_threaded_irq() so is there any other need to
> replace the current request_threaded_irq()?

No, it's certainly ok to keep using request_threaded_irq, my suggestion was
only in order to improve performance, which it will not do as Mark commented.

I don't any strong reason one way or another.

	Arnd
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