On Wed, 14 Nov 2007 22:50:17 -0800
David Brownell <[EMAIL PROTECTED]> wrote:
> > Since this is the code that runs under the lock
>
> No, there's more than that. This is what runs under it in
> the hot paths, yes, but the gpio request/free paths do
> more work than this. (That includes direction setting,
> since that can be an implicit request.)
Yeah, I was talking about the hot paths. That's the only place where
raw vs. non-raw performance matters.
> The get/set bit calls are the hot paths. Locking on those paths
> buys us a consistent locking policy, which is obviously correct.
> It's consistent with the request/free paths.
>
> But I think what you're suggesting is that the "requested" flag
> is effectively a long-term lock, so grabbing the spinlock on
> those paths is not necessary. Right?
Exactly. If we add two (quite reasonable) restrictions:
* The GPIO framework must ensure that GPIO chips cannot be removed
when one or more pins have been assigned to a client.
* The client must ensure that it never calls gpio_free()
simultaneously with gpio_[sg]et_value(), adding locking of its own if
necessary.
this should be safe.
Håvard
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