[PATCH mvebu v2 05/10] clk: mvebu: armada-37xx-periph: Fix switching CPU freq from 250 Mhz to 1 GHz

Pali Rohár
2021-01-14T12:42:30Z

It was observed that the workaround introduced by commit 61c40f35f5cd
("clk: mvebu: armada-37xx-periph: Fix switching CPU rate from 300Mhz to
1.2GHz") when base CPU frequency is 1.2 GHz is also required when base
CPU frequency is 1 GHz. Otherwise switching CPU frequency directly from
L2 (250 MHz) to L0 (1 GHz) causes a crash.

When base CPU frequency is just 800 MHz no crashed were observed during
switch from L2 to L0.

Signed-off-by: Pali Rohár <pali@kernel.org>
Fixes: 2089dc33ea0e ("clk: mvebu: armada-37xx-periph: add DVFS support for cpu clocks")
Cc: stable@vger.kernel.org # 61c40f35f5cd ("clk: mvebu: armada-37xx-periph: Fix switching CPU rate from 300Mhz to 1.2GHz")
---
drivers/clk/mvebu/armada-37xx-periph.c | 12 +++++++-----
1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/drivers/clk/mvebu/armada-37xx-periph.c b/drivers/clk/mvebu/armada-37xx-periph.c
index 6507bd2c5f31..b15e177bea7e 100644
--- a/drivers/clk/mvebu/armada-37xx-periph.c
+++ b/drivers/clk/mvebu/armada-37xx-periph.c
@@ -487,8 +487,10 @@ static long clk_pm_cpu_round_rate(struct clk_hw *hw, unsigned long rate,
}

/*
- * Switching the CPU from the L2 or L3 frequencies (300 and 200 Mhz
- * respectively) to L0 frequency (1.2 Ghz) requires a significant
+ * Workaround when base CPU frequnecy is 1000 or 1200 MHz
+ *
+ * Switching the CPU from the L2 or L3 frequencies (250/300 or 200 MHz
+ * respectively) to L0 frequency (1/1.2 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
@@ -498,15 +500,15 @@ static long clk_pm_cpu_round_rate(struct clk_hw *hw, unsigned long rate,
* 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)
+ * 1. First switch from L2/L3 (200/250/300 MHz) to L1 (500/600 MHz)
* 2. Sleep 20ms for stabling VDD voltage
- * 3. Then switch from L1(600MHZ) to L0(1200Mhz).
+ * 3. Then switch from L1 (500/600 MHz) to L0 (1000/1200 MHz).
*/
static void clk_pm_cpu_set_rate_wa(unsigned long rate, struct regmap *base)
{
unsigned int cur_level;

- if (rate != 1200 * 1000 * 1000)
+ if (rate < 1000 * 1000 * 1000)
return;

regmap_read(base, ARMADA_37XX_NB_CPU_LOAD, &cur_level);
--
2.20.1