Messages in this thread | | | Date | Thu, 24 Jun 2010 11:06:23 +1200 | From | Ryan Mallon <> | Subject | Re: [RFC PATCH] Rework gpio cansleep (was Re: gpiolib and sleeping gpios) |
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On 06/24/2010 10:53 AM, Jamie Lokier wrote: > Ryan Mallon wrote: >> On 06/23/2010 04:37 PM, David Brownell wrote: >> I'm not. Some gpios, such as those on io expanders, may sleep in their >> implementations of the gpio_(set/get) functions. > > I'm having a hard time figuring out where some GPIOs I'm using fit > into this picture. > > I have some hardware that is currently using a 2.4.26 kernel, but I > look from time to time at forward-porting all the drivers to 2.6.recent. > > It has an I2C driven GPIO expander, with a watchdog reset chip hanging > off the expander. > > The watchdog is kept alive off the back end of a timer BH, which means > the I2C GPIO routines are written to be safe in BH context (which > isn't sleepable), but they can't be used in IRQ context because the > necessary spin_lock_irqsave() would turn off interrupts for too long > for other subsystems to function properly.
Do the implementations of the get/set calls for the io expander gpios sleep at all?
> How should I flag those GPIO routines in your scheme? They're safe to > use in some non-sleeping contexts, but not safe in irq context.
The idea in my proposal is to use gpio_request in a driver if the requested gpio can never sleep (ie because of the context it is used in), and gpio_request_cansleep if the gpio is never used from non-sleep safe context in a driver. I suggested stripping back the patch to just add the gpio_request_cansleep function.
In the current code, if a driver ever calls gpio_(set/get)_value on a gpio then you cannot pass a sleeping gpio to that driver. The request will succeed, but you will get warnings with the get/get calls are made. My idea is basically to move the denotation of whether a gpio will be used in non-sleep safe context to the gpio request.
~Ryan
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