linux-kernel - [PATCH 4.19 60/84] cpufreq: armada-37xx: forbid cpufreq for 1.2 GHz variant

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Date:   Tue, 24 Aug 2021 13:02:26 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     Marek Behún <kabel@...nel.org>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH 4.19 60/84] cpufreq: armada-37xx: forbid cpufreq for 1.2 GHz variant

From: Marek Behún <kabel@...nel.org>

[ Upstream commit 484f2b7c61b9ae58cc00c5127bcbcd9177af8dfe ]

The 1.2 GHz variant of the Armada 3720 SOC is unstable with DVFS: when
the SOC boots, the WTMI firmware sets clocks and AVS values that work
correctly with 1.2 GHz CPU frequency, but random crashes occur once
cpufreq driver starts scaling.

We do not know currently what is the reason:
- it may be that the voltage value for L0 for 1.2 GHz variant provided
  by the vendor in the OTP is simply incorrect when scaling is used,
- it may be that some delay is needed somewhere,
- it may be something else.

The most sane solution now seems to be to simply forbid the cpufreq
driver on 1.2 GHz variant.

Signed-off-by: Marek Behún <kabel@...nel.org>
Fixes: 92ce45fb875d ("cpufreq: Add DVFS support for Armada 37xx")
Signed-off-by: Viresh Kumar <viresh.kumar@...aro.org>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 drivers/cpufreq/armada-37xx-cpufreq.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/drivers/cpufreq/armada-37xx-cpufreq.c b/drivers/cpufreq/armada-37xx-cpufreq.c
index a36452bd9612..31b5655419b4 100644
--- a/drivers/cpufreq/armada-37xx-cpufreq.c
+++ b/drivers/cpufreq/armada-37xx-cpufreq.c
@@ -102,7 +102,11 @@ struct armada_37xx_dvfs {
 };
 
 static struct armada_37xx_dvfs armada_37xx_dvfs[] = {
-	{.cpu_freq_max = 1200*1000*1000, .divider = {1, 2, 4, 6} },
+	/*
+	 * The cpufreq scaling for 1.2 GHz variant of the SOC is currently
+	 * unstable because we do not know how to configure it properly.
+	 */
+	/* {.cpu_freq_max = 1200*1000*1000, .divider = {1, 2, 4, 6} }, */
 	{.cpu_freq_max = 1000*1000*1000, .divider = {1, 2, 4, 5} },
 	{.cpu_freq_max = 800*1000*1000,  .divider = {1, 2, 3, 4} },
 	{.cpu_freq_max = 600*1000*1000,  .divider = {2, 4, 5, 6} },
-- 
2.30.2