Re: [PATCH 2/2] regmap: Make regmap-mmio usable from different contexts

[Lars-Peter Clausen <lars@metafoo.de>]

On 05/23/2013 04:31 PM, Mark Brown wrote:
> On Thu, May 23, 2013 at 04:20:27PM +0200, Lars-Peter Clausen wrote:
>> On 05/23/2013 04:05 PM, Mark Brown wrote:
> 
>>> This seems really invasive, why not just have the lock that gets passed
>>> in point to a struct which has both the lock and the flags?  As far as
>>> the core is concerned the lock is just whatever data is required to do
>>> the locking, the fact that it's actually two values is an implementation
>>> detail of this locking implementation.
> 
>> I think that won't work. spin_lock_irqsave() will write to the flags
>> parameter before it has successfully taken the look. So if a process running
>> on another CPU tries to acquire the the lock while it is already held we'll
>> end up overwriting the flags. E.g:
> 
> So you'd have to allocate a struct on the stack with a pointer and the
> flags in it and initialise the pointer.  Not awesome but not the end of
> the world.

I'm not sure I understand what you mean. This needs to be done for each
caller of a lock()/unlock() pair. We can't allocate the flags on the stack
inside the lock() function since the stack will be gone once the function exits.

- Lars