[PATCH v5 10/10] clk: fix set_rate_range when current rate is out of range

[Jerome Brunet]

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: 1c8e600440c7 ("clk: Add rate constraints to clocks")
Tested-by: Maxime Ripard <maxime.rip...@free-electrons.com>
Acked-by: Michael Turquette <mturque...@baylibre.com>
Signed-off-by: Jerome Brunet <jbru...@baylibre.com>
---
 drivers/clk/clk.c | 37 +++++++++++++++++++++++++++++++++----
 1 file changed, 33 insertions(+), 4 deletions(-)

diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c
index edd965d8f41d..369933831705 100644
--- a/drivers/clk/clk.c
+++ b/drivers/clk/clk.c
@@ -2010,6 +2010,7 @@ 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;
@@ -2026,10 +2027,38 @@ 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) {
-               clk->min_rate = min;
-               clk->max_rate = max;
-               ret = clk_core_set_rate_nolock(clk->core, clk->core->req_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;
+
+       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)
-- 
2.14.3