Re: [PATCH] clk: Fix race conditions between clk_set_parent() andclk_enable()

From: Saravana Kannan
Date: Tue May 15 2012 - 16:09:02 EST

On 05/15/2012 01:00 PM, Sascha Hauer wrote:
On Tue, May 15, 2012 at 12:51:06PM -0700, Saravana Kannan wrote:
ret = clk->ops->set_parent(clk->hw, i);

You call ->set_parent while holding a spinlock. This won't work with i2c

I did account for that. I explained it in the commit text. Please
let me know if any part of that is not clear or is not correct.

I missed this part in the commit log. I have no idea whether we can live
with this limitation though.


It's not really an artificial limitation of the patch. This has to be enforced if the clock is to be managed correctly while allowing .set_parent to NOT be atomic.

There is no way to guarantee that the enable/disable is properly propagated to the parent clock if we can't guarantee mutual exclusion between changing parents and calling enable/disable.

Since we can't do mutual exclusion be using spinlock (since .set_parent is NOT atomic for these clocks), then only other way of ensuring mutual exclusion is to force an unprepare and then mutually exclude a prepare while changing the parent. This by association (can't enable unprepared clock) mutually excludes the changing of parent and calling enable/disable.


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