Do not deprecate binary semaphore or do allow mutex in software interrupt contexts

[Matti Linnanvuori <mattilinnanvuori@yahoo.com>]

Peter Zijlstra <peterz@infradead.org>:
> Yes it is.

Why do you think it is broken?

> If you have to wait a long time in an atomic context you've done
> something wrong.

I saw an implementation where there were two atomic contexts, one to initiate reading and another to complete the reading. 
That way, there was no busy wait for a long time in an atomic context.

> If you're only reading it from an atomic context you
> might consider storing a copy that can be quickly updated and protect
> that using a spinlock.

You suggested that a user-space task read from the device. 
But that includes more context switching and therefore consumes more resources than reading just from an atomic context.

> Not being too familiar with the timer stuff, it smells wrong what you
> say.

Why?




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