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Commit 6562fbcf authored by Jerome Brunet's avatar Jerome Brunet Committed by Michael Turquette
Browse files

clk: fix set_rate_range when current rate is out of range 



Calling clk_core_set_rate() with core->req_rate is basically a no-op
because of the early bail-out mechanism.

This may leave the clock in inconsistent state if the rate is out the
requested range. Calling clk_core_set_rate() with the closest rate
limit could solve the problem but:
- The underlying determine_rate() callback needs to account for this
  corner case (rounding within the range, if possible)
- if only round_rate() is available, we rely on luck unfortunately.

Fixes: 1c8e6004 ("clk: Add rate constraints to clocks")
Tested-by: default avatarMaxime Ripard <maxime.ripard@free-electrons.com>
Acked-by: default avatarMichael Turquette <mturquette@baylibre.com>
Signed-off-by: default avatarJerome Brunet <jbrunet@baylibre.com>
Signed-off-by: default avatarMichael Turquette <mturquette@baylibre.com>
Link: lkml.kernel.org/r/20171201215200.23523-11-jbrunet@baylibre.com
parent 55e9b8b7

drivers/clk/clk.c

+33 −4
Original line number Diff line number Diff line
@@ -2000,6 +2000,7 @@ EXPORT_SYMBOL_GPL(clk_set_rate_exclusive); 
int clk_set_rate_range(struct clk *clk, unsigned long min, unsigned long max)

{

	int ret = 0;

	unsigned long old_min, old_max, rate;



	if (!clk)

		return 0;
@@ -2016,10 +2017,38 @@ int clk_set_rate_range(struct clk *clk, unsigned long min, unsigned long max) 
	if (clk->exclusive_count)

		clk_core_rate_unprotect(clk->core);



	if (min != clk->min_rate || max != clk->max_rate) {

	/* Save the current values in case we need to rollback the change */

	old_min = clk->min_rate;

	old_max = clk->max_rate;

	clk->min_rate = min;

	clk->max_rate = max;

		ret = clk_core_set_rate_nolock(clk->core, clk->core->req_rate);



	rate = clk_core_get_rate_nolock(clk->core);

	if (rate < min || rate > max) {

		/*

		 * FIXME:

		 * We are in bit of trouble here, current rate is outside the

		 * the requested range. We are going try to request appropriate

		 * range boundary but there is a catch. It may fail for the

		 * usual reason (clock broken, clock protected, etc) but also

		 * because:

		 * - round_rate() was not favorable and fell on the wrong

		 *   side of the boundary

		 * - the determine_rate() callback does not really check for

		 *   this corner case when determining the rate

		 */



		if (rate < min)

			rate = min;

		else

			rate = max;



		ret = clk_core_set_rate_nolock(clk->core, rate);

		if (ret) {

			/* rollback the changes */

			clk->min_rate = old_min;

			clk->max_rate = old_max;

		}

	}



	if (clk->exclusive_count)