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imx233: rework cpu frequency scaling

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When changing the cpu frequency, it is important to make sure that
HBUS stays at a reasonable frequency otherwise the chip will
crash. Special care is needed about auto-slow and clk_p/clk_h
ratio on intermediate steps.

Change-Id: Ief9f68ddf286caabe75c879718dac5027ab1560f
This commit is contained in:
Amaury Pouly 2012-12-26 01:12:24 +01:00
parent e2da3f47d3
commit 09e6b890e6
1 changed files with 23 additions and 8 deletions
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31
firmware/target/arm/imx233/system-imx233.c
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@ -158,16 +158,31 @@ void udelay(unsigned us)
#ifdef HAVE_ADJUSTABLE_CPU_FREQ
void set_cpu_frequency(long frequency)
{
(void) frequency;
/* don't change the frequency if it is useless (changes are expensive) */
if(cpu_frequency == frequency)
return;
cpu_frequency = frequency;
/* disable auto-slow (enable back afterwards) */
imx233_clkctrl_enable_auto_slow(false);
/* go back to a known state in safe way:
* clk_p@24 MHz
* clk_h@6 MHz
* WARNING: we must absolutely avoid that clk_h be too low or too high
* during the change. We first change the clk_p/clk_h ratio to 4 so
* that it cannot be too high (480/4=120 MHz max) or too low
* (24/4=6 MHz min). Then we switch clk_p to bypass. We chose a ratio of 4
* which is greater than all clk_p/clk_h ratios used below so that further
* changes are safe too */
imx233_clkctrl_set_clock_divisor(CLK_HBUS, 4);
imx233_clkctrl_set_bypass_pll(CLK_CPU, true);
switch(frequency)
{
case IMX233_CPUFREQ_454_MHz:
/* go back to a known state: everything at 24MHz ! */
imx233_clkctrl_set_bypass_pll(CLK_CPU, true);
imx233_clkctrl_set_clock_divisor(CLK_HBUS, 1);
/* set VDDD to 1.550 mV (brownout at 1.450 mV) */
imx233_power_set_regulator(REGULATOR_VDDD, 1550, 1450);
/* clk_h@clk_p/2 */
/* clk_h@clk_p/3 */
imx233_clkctrl_set_clock_divisor(CLK_HBUS, 3);
/* clk_p@ref_cpu/1*18/19 */
imx233_clkctrl_set_fractional_divisor(CLK_CPU, 19);
@ -180,9 +195,6 @@ void set_cpu_frequency(long frequency)
* clk_h@130.91 MHz */
break;
case IMX233_CPUFREQ_261_MHz:
/* go back to a known state: everything at 24MHz ! */
imx233_clkctrl_set_bypass_pll(CLK_CPU, true);
imx233_clkctrl_set_clock_divisor(CLK_HBUS, 1);
/* set VDDD to 1.275 mV (brownout at 1.175 mV) */
imx233_power_set_regulator(REGULATOR_VDDD, 1275, 1175);
/* clk_h@clk_p/2 */
@ -200,6 +212,9 @@ void set_cpu_frequency(long frequency)
default:
break;
}
/* enable auto slow again */
imx233_clkctrl_enable_auto_slow(true);
}
#endif