[lkml]   [2011]   [Feb]   [1]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
SubjectRe: Locking in the clk API, part 2: clk_prepare/clk_unprepare
2011/2/2 Russell King - ARM Linux <>:
> On Tue, Feb 01, 2011 at 04:22:03PM +0100, Uwe Kleine-König wrote:
>> Full ack.  (I wonder if you misunderstood me or wanted to put my
>> statement into more words.  Jassi didn't like that a clk_enable without
>> a previous clk_prepare worked on some platforms and on others it
>> doesn't.  With BUG_ON(clk->ops->prepare && !clk->prepare_count) in
>> clk_enable we have exactly this situation.)
> Even with a NULL clk->ops->prepare function, we still want drivers to
> have called clk_prepare().  So we can do something like:
>        if (WARN_ON(clk->prepare_count == 0))
>                return -EINVAL;
> in clk_enable() should be sufficient and noisy enough not to be missed.
> I'd avoid BUG_ON() here as that will take the system down, which may
> increase the chances of getting useful bug reports.

Having thought about it, I think it's not necessary to immediately catch
drivers that work on some platforms and not on others -- a mere comment
'please add clk_prepare' during code review or a patch adding 'clk_prepare'
later upon stumbling across a platform on which the driver doesn't work,
should be OK. Let us not fret about it.

That leaves us with only having to ensure that :-
a) No two calls to clk_prepare/unprepare _hooks_ are consecutive.
b) clk_prepare is done on the clock (not necessarily by the driver
under consideration) before calls to clk_enable.

I think (a) is already easily managed by having the prepare_count,
and (b) can be reasonably managed by what Russell suggests above.

So, FWIW, I am for the idea.

To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to
More majordomo info at
Please read the FAQ at

 \ /
  Last update: 2011-02-02 03:35    [W:0.100 / U:74.520 seconds]
©2003-2018 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site