OMAPDSS: fix dss_fck clock rate rounding

DSS func clock is calculated with prate / div * m. However, the current
omapdss code calculates it with prate * m / div, which yields a slightly
different result when there's a remainder. For example, 432000000 / 14 *
2 = 61714284, but 432000000 * 2 / 14 = 61714285.

In addition to that, the clock framework wants the clock rate given with
clk_set_rate to be higher than the actual (truncated) end result. So, if
prate is 432000000, and div is 14, the real result is 30857142.8571...
We need to call clk_set_rate with 30857143, which gives us a clock of
30857142. That's why we need to use DIV_ROUND_UP() when calling
clk_set_rate.

This patch fixes the clock calculation.

Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>

1 files changed, 11 insertions, 6 deletions

diff --git a/drivers/video/omap2/dss/dss.c b/drivers/video/omap2/dss/dss.c
index fdd32e8d9212..b9f6f245d4a1 100644
--- a/drivers/video/omap2/dss/dss.c
+++ b/drivers/video/omap2/dss/dss.c
@@ -480,6 +480,7 @@ bool dss_div_calc(unsigned long fck_min, dss_div_calc_func func, void *data)
         unsigned long fck_hw_max;
         unsigned long fckd_hw_max;
         unsigned long prate;
+        unsigned m;
 
         if (dss.dpll4_m4_ck == NULL) {
                 /*
@@ -495,15 +496,16 @@ bool dss_div_calc(unsigned long fck_min, dss_div_calc_func func, void *data)
         fck_hw_max = dss_feat_get_param_max(FEAT_PARAM_DSS_FCK);
         fckd_hw_max = dss.feat->fck_div_max;
 
-        prate = dss_get_dpll4_rate() * dss.feat->dss_fck_multiplier;
+        m = dss.feat->dss_fck_multiplier;
+        prate = dss_get_dpll4_rate();
 
         fck_min = fck_min ? fck_min : 1;
 
-        fckd_start = min(prate / fck_min, fckd_hw_max);
-        fckd_stop = max(DIV_ROUND_UP(prate, fck_hw_max), 1ul);
+        fckd_start = min(prate * m / fck_min, fckd_hw_max);
+        fckd_stop = max(DIV_ROUND_UP(prate * m, fck_hw_max), 1ul);
 
         for (fckd = fckd_start; fckd >= fckd_stop; --fckd) {
-                fck = prate / fckd;
+                fck = prate / fckd * m;
 
                 if (func(fckd, fck, data))
                         return true;
@@ -521,7 +523,8 @@ int dss_set_clock_div(struct dss_clock_info *cinfo)
                 prate = clk_get_rate(clk_get_parent(dss.dpll4_m4_ck));
                 DSSDBG("dpll4_m4 = %ld\n", prate);
 
-                r = clk_set_rate(dss.dpll4_m4_ck, prate / cinfo->fck_div);
+                r = clk_set_rate(dss.dpll4_m4_ck,
+                                DIV_ROUND_UP(prate, cinfo->fck_div));
                 if (r)
                         return r;
         } else {
@@ -531,7 +534,9 @@ int dss_set_clock_div(struct dss_clock_info *cinfo)
 
         dss.dss_clk_rate = clk_get_rate(dss.dss_clk);
 
-        WARN_ONCE(dss.dss_clk_rate != cinfo->fck, "clk rate mismatch");
+        WARN_ONCE(dss.dss_clk_rate != cinfo->fck,
+                        "clk rate mismatch: %lu != %lu", dss.dss_clk_rate,
+                        cinfo->fck);
 
         DSSDBG("fck = %ld (%d)\n", cinfo->fck, cinfo->fck_div);