Re: spinlock_irq & spinlock_irq_save

[Chris Wright <chris@wirex.com>]

* Daniele Bellucci (bellucda@tiscali.it) wrote:
> Hi list,
> i'm a bit confused about the usage of spinlock_irq & spinlock_irq_save...
> when do i need to save flags? ... and when i don't need to take care about  flags?
> 

spin_lock_irq/spin_unlock_irq will blindly disable irq then re-enable.
this is fine if you _know_ irq is enabled.

spin_lock_irqsave/spin_unlock_irqrestore allows you to save the current
irq state, disable, then restore to original state.  this is required
when you _don't know_ if the irq was originally enabled.

imagine:  irq off -> spin_lock_irq/spin_unlock_irq -> oops, irq is now on

thanks,
-chris
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