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SubjectRe: Locking in the clk API, part 2: clk_prepare/clk_unprepare
On 02/01/2011 07:24 AM, Russell King - ARM Linux wrote:
> A simpler way to write this is:
>
> int clk_prepare(struct clk *clk)
> {
> int ret = 0;
>
> mutex_lock(&clk->mutex);
> if (clk->prepared == 0)
> ret = clk->ops->prepare(clk);
> if (ret == 0)
> clk->prepared++;
> mutex_unlock(&clk->mutex);
>
> return ret;
> }
>
> I think we want to take a common mutex not only for clk_prepare(), but
> also for clk_set_rate(). If prepare() is waiting for a PLL to lock,
> we don't want a set_rate() interfering with that.

Looks like this is the best acknowledgment/response I can expect to get
from Russell on this point that I raised.

Jeremy,

When you update the comments/doc to indicate clk_prepare/unprepare is
not atomic, can you also update the comment for set_rate() and mark it
as non-atomic?

Thanks for starting this thread. My efforts to reignite the other thread
didn't go anywhere. Glad to see it's moving forward.

> I'd also be tempted at this stage to build-in a no-op dummy clock,
> that being the NULL clk:
>[snip]
> as we have various platforms defining a dummy struct clk as a way of
> satisfying various driver requirements. These dummy clocks are exactly
> that - they're complete no-ops.

Unrelated to this thread, but I Ack this request too.

-Saravana

--
Sent by an employee of the Qualcomm Innovation Center, Inc.
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum.


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