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

From: "Pali Rohár" <pali@kernel.org>
To: Gregory Clement <gregory.clement@bootlin.com>,
	Andrew Lunn <andrew@lunn.ch>,
	Michael Turquette <mturquette@baylibre.com>,
	Stephen Boyd <sboyd@kernel.org>,
	linux-arm-kernel@lists.infradead.org,
	linux-kernel@vger.kernel.org, linux-clk@vger.kernel.org
Cc: "Marek Behún" <kabel@kernel.org>,
	"Miquel Raynal" <miquel.raynal@bootlin.com>,
	"Tomasz Maciej Nowak" <tmn505@gmail.com>,
	"Luka Perkov" <luka.perkov@sartura.hr>,
	"Andre Heider" <a.heider@gmail.com>,
	"Vladimir Vid" <vladimir.vid@sartura.hr>,
	"Russell King" <rmk+kernel@armlinux.org.uk>,
	"Gérald Kerma" <gerald@gk2.net>,
	"Konstantin Porotchkin" <kostap@marvell.com>
Subject: [PATCH mvebu v2 05/10] clk: mvebu: armada-37xx-periph: Fix switching CPU freq from 250 Mhz to 1 GHz
Date: Thu, 14 Jan 2021 13:40:27 +0100	[thread overview]
Message-ID: <20210114124032.12765-6-pali@kernel.org> (raw)
In-Reply-To: <20210114124032.12765-1-pali@kernel.org>

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

