Messages in this thread | | | Date | Tue, 1 Feb 2011 20:32:01 +0100 | From | Uwe Kleine-König <> | Subject | Re: Locking in the clk API, part 2: clk_prepare/clk_unprepare |
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On Tue, Feb 01, 2011 at 05:06:37PM +0000, Russell King - ARM Linux wrote: > On Tue, Feb 01, 2011 at 04:53:44PM +0100, Uwe Kleine-König wrote: > > On Tue, Feb 01, 2011 at 03:24:58PM +0000, Russell King - ARM Linux wrote: > > > On Tue, Feb 01, 2011 at 04:18:46PM +0100, Uwe Kleine-König wrote: > > > > yeah, didn't thought about multiple consumers, so (as Jeremy suggested) > > > > the right thing is to sleep until CLK_BUSY is cleared. > > > > > > 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; > > > } > > But you cannot call this in atomic context when you know the clock is > > already prepared. > > So? You're not _supposed_ to call it from any atomic context ever. My motivation for a more complicated clk_prepare was to make clk_prepare atomic when that's possible (i.e. when the clk is already prepared) and call it before the enable callback in clk_enable. Then everything behaves nicely even if clk_enable is called from atomic context provided that the clock was prepared before (or doesn't need to).
If a driver writer doesn't know that a certain clock might need to sleep at some point he runs into an atomic might_sleep with your approach and with mine.
Best regards Uwe
-- Pengutronix e.K. | Uwe Kleine-König | Industrial Linux Solutions | http://www.pengutronix.de/ | -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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