To: linux-kernel@vger.kernel.org
From: Rich Walker <rw@shadow.org.uk>
Subject: Re: best way to handle LEDs
Date: Thu, 03 Nov 2005 14:26:28 +0000
Organization: Shadow Robot Company
Message-ID: <m3oe51erjf.fsf@shadow.org.uk>
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Russell King <rmk+lkml@arm.linux.org.uk> writes:

>
> I also have issues with a generic GPIO layer.  As I mentioned in the
> past, there's serious locking issues with any generic abstraction of
> GPIOs.
>
> 1. You want to be able to change GPIO state from interrupts.  This
>    implies you can not sleep in GPIO state changing functions.
>
> 2. Some GPIOs are implemented on I2C devices.  This means that to
>    change state, you must sleep.
>
> (1) and (2) are incompatible requirements, so you can not offer a
> generic interface for these GPIOs which has a consistent behaviour -
> where users of the interface know whether the function may sleep or
> may be used from interrupt context.
>

So you have a request_gpio API, where you specify usage characteristics
and get back a handle?

cheers, Rich.

-- 
rich walker         |  Shadow Robot Company | rw@shadow.org.uk
technical director     251 Liverpool Road   |
need a Hand?           London  N1 1LX       | +UK 20 7700 2487
www.shadow.org.uk/products/newhand.shtml

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