Re: [PATCH] gpio: omap: use raw locks for locking

[Sebastian Andrzej Siewior <bigeasy@linutronix.de>]

On 07/27/2015 02:50 PM, Linus Walleij wrote:
> Patch applied.
thanks.

> 
> Now this question appear in my head:
> 
> Is drivers/gpio full of stuff that will not work with the -RT kernel,
> and is this a change that should be done mutatis mutandis on
> all the GPIO drivers?

I described two call paths where you need a rawlock_t. If your gpio
driver uses irq_chip_generic then you a rawlock here and things should
be fine.

In general: If your gpio controller acts as an interrupts controller
(that is via chained handler) then you need the raw-locks if you need
any locking (if you have a write 1 to mask/unmask/enable/disable
register then you probably don't need any locking here at all). If the
gpio controller does not act as an interrupt controller than the
spinlock_t type should be enough.
If your gpio-interrupt controller requests its interrupt via
requested_threaded_irq() then it should do handle_nested_irq() and a
mutex is probably used for locking.

Using request_irq() with "0" flags is kind of broken. It works in
IRQ-context and delivers the interrupts with generic_handle_irq() and
this one passes it the handler (like handle_edge_irq() /
handle_level_irq()) which takes a raw_lock. Now, if you boot the
vanilla kernel with threadedirq then the irq-handler runs in threaded
context and you can't take a spinlock here anymore. So I think you
should use here IRQF_NO_THREAD here (and the raw lock type). I added
tglx on Cc: to back up because it is Monday.

> Yours,
> Linus Walleij
> 

Sebastian