ARM: OMAP2+: clock: allow omap2_dpll_round_rate() to round to next-lowest rate

Change the behavior of omap2_dpll_round_rate() to round to either the
exact rate requested, or the next lowest rate that the clock is able to
provide.

This is not an ideal fix, but is intended to provide a relatively safe
way for drivers to set PLL rates, until a better solution can be
implemented.

For the time being, omap3_noncore_dpll_set_rate() is still allowed to
set its rate to something other than what the caller requested; but will
warn when this occurs.

Cc: Tomi Valkeinen <tomi.valkeinen@ti.com>
Cc: Mike Turquette <mturquette@linaro.org>
Signed-off-by: Paul Walmsley <paul@pwsan.com>

2 files changed, 32 insertions, 9 deletions

diff --git a/arch/arm/mach-omap2/clkt_dpll.c b/arch/arm/mach-omap2/clkt_dpll.c
index 332af927f4d3..85701142c5fc 100644
--- a/arch/arm/mach-omap2/clkt_dpll.c
+++ b/arch/arm/mach-omap2/clkt_dpll.c
@@ -293,10 +293,13 @@ long omap2_dpll_round_rate(struct clk_hw *hw, unsigned long target_rate,
 {
         struct clk_hw_omap *clk = to_clk_hw_omap(hw);
         int m, n, r, scaled_max_m;
+        int min_delta_m = INT_MAX, min_delta_n = INT_MAX;
         unsigned long scaled_rt_rp;
         unsigned long new_rate = 0;
         struct dpll_data *dd;
         unsigned long ref_rate;
+        long delta;
+        long prev_min_delta = LONG_MAX;
         const char *clk_name;
 
         if (!clk || !clk->dpll_data)
@@ -342,23 +345,34 @@ long omap2_dpll_round_rate(struct clk_hw *hw, unsigned long target_rate,
                 if (r == DPLL_MULT_UNDERFLOW)
                         continue;
 
+                /* skip rates above our target rate */
+                delta = target_rate - new_rate;
+                if (delta < 0)
+                        continue;
+
+                if (delta < prev_min_delta) {
+                        prev_min_delta = delta;
+                        min_delta_m = m;
+                        min_delta_n = n;
+                }
+
                 pr_debug("clock: %s: m = %d: n = %d: new_rate = %lu\n",
                          clk_name, m, n, new_rate);
 
-                if (target_rate == new_rate) {
-                        dd->last_rounded_m = m;
-                        dd->last_rounded_n = n;
-                        dd->last_rounded_rate = target_rate;
+                if (delta == 0)
                         break;
-                }
         }
 
-        if (target_rate != new_rate) {
+        if (prev_min_delta == LONG_MAX) {
                 pr_debug("clock: %s: cannot round to rate %lu\n",
                          clk_name, target_rate);
                 return ~0;
         }
 
-        return target_rate;
+        dd->last_rounded_m = min_delta_m;
+        dd->last_rounded_n = min_delta_n;
+        dd->last_rounded_rate = target_rate - prev_min_delta;
+
+        return dd->last_rounded_rate;
 }
 
diff --git a/arch/arm/mach-omap2/dpll3xxx.c b/arch/arm/mach-omap2/dpll3xxx.c
index 6d7ba37e2257..b6860bfb05b3 100644
--- a/arch/arm/mach-omap2/dpll3xxx.c
+++ b/arch/arm/mach-omap2/dpll3xxx.c
@@ -478,6 +478,7 @@ int omap3_noncore_dpll_set_rate(struct clk_hw *hw, unsigned long rate,
 {
         struct clk_hw_omap *clk = to_clk_hw_omap(hw);
         struct clk *new_parent = NULL;
+        unsigned long rrate;
         u16 freqsel = 0;
         struct dpll_data *dd;
         int ret;
@@ -505,8 +506,16 @@ int omap3_noncore_dpll_set_rate(struct clk_hw *hw, unsigned long rate,
                 __clk_prepare(dd->clk_ref);
                 clk_enable(dd->clk_ref);
 
-                if (dd->last_rounded_rate != rate)
-                        rate = __clk_round_rate(hw->clk, rate);
+                /* XXX this check is probably pointless in the CCF context */
+                if (dd->last_rounded_rate != rate) {
+                        rrate = __clk_round_rate(hw->clk, rate);
+                        if (rrate != rate) {
+                                pr_warn("%s: %s: final rate %lu does not match desired rate %lu\n",
+                                        __func__, __clk_get_name(hw->clk),
+                                        rrate, rate);
+                                rate = rrate;
+                        }
+                }
 
                 if (dd->last_rounded_rate == 0)
                         return -EINVAL;