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path: root/drivers/clk/mvebu/armada-37xx-periph.c
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Diffstat (limited to 'drivers/clk/mvebu/armada-37xx-periph.c')
-rw-r--r--drivers/clk/mvebu/armada-37xx-periph.c38
1 files changed, 38 insertions, 0 deletions
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;