Espressobi: Fix switching CPU rate from 300Mhz to 1.2GHz

patch/kernel/mvebu64-next/1-2-clk-mvebu-armada-37xx-periph-Fix-switching-CPU-rate-from-300Mhz-to-1.2GHz.patch

@@ -0,0 +1,63 @@
+diff --git a/drivers/clk/mvebu/armada-37xx-periph.c b/drivers/clk/mvebu/armada-37xx-periph.c
+index 6860bd5a37c5..44e4e27eddad 100644
+--- a/drivers/clk/mvebu/armada-37xx-periph.c
++++ b/drivers/clk/mvebu/armada-37xx-periph.c
+@@ -35,6 +35,7 @@
+ #define CLK_SEL		0x10
+ #define CLK_DIS		0x14
+ 
++#define  ARMADA_37XX_DVFS_LOAD_1 1
+ #define LOAD_LEVEL_NR	4
+ 
+ #define ARMADA_37XX_NB_L0L1	0x18
+@@ -507,6 +508,40 @@ static long clk_pm_cpu_round_rate(struct clk_hw *hw, unsigned long rate,
+ 	return -EINVAL;
+ }
+ 
++/*
++ * Switching the CPU from the L2 or L3 frequencies (300 and 200 Mhz
++ * respectively) to L0 frequency (1.2 Ghz) requires a significant
++ * amount of time to let VDD stabilize to the appropriate
++ * voltage. This amount of time is large enough that it cannot be
++ * covered by the hardware countdown register. Due to this, the CPU
++ * might start operating at L0 before the voltage is stabilized,
++ * leading to CPU stalls.
++ *
++ * To work around this problem, we prevent switching directly from the
++ * L2/L3 frequencies to the L0 frequency, and instead switch to the L1
++ * frequency in-between. The sequence therefore becomes:
++ * 1. First switch from L2/L3(200/300MHz) to L1(600MHZ)
++ * 2. Sleep 20ms for stabling VDD voltage
++ * 3. Then switch from L1(600MHZ) to L0(1200Mhz).
++ */
++static void clk_pm_cpu_set_rate_wa(unsigned long rate, struct regmap *base)
++{
++	unsigned int cur_level;
++
++	if (rate != 1200 * 1000 * 1000)
++		return;
++
++	regmap_read(base, ARMADA_37XX_NB_CPU_LOAD, &cur_level);
++	cur_level &= ARMADA_37XX_NB_CPU_LOAD_MASK;
++	if (cur_level <= ARMADA_37XX_DVFS_LOAD_1)
++		return;
++
++	regmap_update_bits(base, ARMADA_37XX_NB_CPU_LOAD,
++			   ARMADA_37XX_NB_CPU_LOAD_MASK,
++			   ARMADA_37XX_DVFS_LOAD_1);
++	msleep(20);
++}
++
+ static int clk_pm_cpu_set_rate(struct clk_hw *hw, unsigned long rate,
+ 			       unsigned long parent_rate)
+ {
+@@ -537,6 +572,9 @@ static int clk_pm_cpu_set_rate(struct clk_hw *hw, unsigned long rate,
+ 			 */
+ 			reg = ARMADA_37XX_NB_CPU_LOAD;
+ 			mask = ARMADA_37XX_NB_CPU_LOAD_MASK;
++
++			clk_pm_cpu_set_rate_wa(rate, base);
++
+ 			regmap_update_bits(base, reg, mask, load_level);
+ 
+ 			return rate;