[ARM] 4254/1: i.MX/MX1 CPU Frequency scaling honor boot loader set BCLK_DIV.

The minimal bus clock prescaler should be kept at value
selected by the board / boot loader designer.
Switching frequency above startup limit could
lead to the external memory/devices misbehave.

Signed-off-by: Pavel Pisa <pisa@cmp.felk.cvut.cz>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

1 files changed, 6 insertions, 3 deletions

diff --git a/arch/arm/mach-imx/cpufreq.c b/arch/arm/mach-imx/cpufreq.c
index 4f66e90db74f..43525ee504d5 100644
--- a/arch/arm/mach-imx/cpufreq.c
+++ b/arch/arm/mach-imx/cpufreq.c
@@ -50,6 +50,7 @@
 #define CR_920T_ASYNC_MODE      0xC0000000
 
 static u32 mpctl0_at_boot;
+static u32 bclk_div_at_boot;
 
 static void imx_set_async_mode(void)
 {
@@ -182,7 +183,7 @@ static int imx_set_target(struct cpufreq_policy *policy,
         unsigned long flags;
         long freq;
         long sysclk;
-        unsigned int bclk_div = 1;
+        unsigned int bclk_div = bclk_div_at_boot;
 
         /*
          * Some governors do not respects CPU and policy lower limits
@@ -202,7 +203,7 @@ static int imx_set_target(struct cpufreq_policy *policy,
 
         sysclk = imx_get_system_clk();
 
-        if (freq > sysclk + 1000000) {
+        if (freq > sysclk / bclk_div_at_boot + 1000000) {
                 freq = imx_compute_mpctl(&mpctl0, mpctl0_at_boot, freq, relation);
                 if (freq < 0) {
                         printk(KERN_WARNING "imx: target frequency %ld Hz cannot be set\n", freq);
@@ -217,6 +218,8 @@ static int imx_set_target(struct cpufreq_policy *policy,
 
                         if(bclk_div > 16)
                                 bclk_div = 16;
+                        if(bclk_div < bclk_div_at_boot)
+                                bclk_div = bclk_div_at_boot;
                 }
                 freq = (sysclk + bclk_div / 2) / bclk_div;
         }
@@ -285,7 +288,7 @@ static struct cpufreq_driver imx_driver = {
 
 static int __init imx_cpufreq_init(void)
 {
-
+        bclk_div_at_boot = __mfld2val(CSCR_BCLK_DIV, CSCR) + 1;
         mpctl0_at_boot = 0;
 
         if((CSCR & CSCR_MPEN) &&