linux-kernel - [PATCH] clk: meson-gxbb: set fclk_div2 as CLK_IS

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Date:   Wed, 13 Jun 2018 14:20:21 +0200
From:   Neil Armstrong <narmstrong@...libre.com>
To:     jbrunet@...libre.com, sboyd@...nel.org, mturquette@...libre.com
Cc:     Neil Armstrong <narmstrong@...libre.com>,
        linux-clk@...r.kernel.org, linux-amlogic@...ts.infradead.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: [PATCH] clk: meson-gxbb: set fclk_div2 as CLK_IS_CRITICAL

On Amlogic Meson GXBB & GXL platforms, the SCPI Cortex-M4 Co-Processor
seems to be dependent on the FCLK_DIV2 to be operationnal.

The issue occured since v4.17-rc1 by freezing the kernel boot when
the 'schedutil' cpufreq governor was selected as default :

  [   12.071837] scpi_protocol scpi: SCP Protocol 0.0 Firmware 0.0.0 version
  domain-0 init dvfs: 4
  [   12.087757] hctosys: unable to open rtc device (rtc0)
  [   12.087907] cfg80211: Loading compiled-in X.509 certificates for regulatory database
  [   12.102241] cfg80211: Loaded X.509 cert 'sforshee: 00b28ddf47aef9cea7'

But when disabling the MMC driver, the boot finished but cpufreq failed to
change the CPU frequency :

  [   12.153045] cpufreq: __target_index: Failed to change cpu frequency: -5

A bisect between v4.16 and v4.16-rc1 gave the 05f814402d61 commit to be
the first bad commit.
This commit added support for the missing clock gates before the fixed PLL
fixed dividers (FCLK_DIVx) and the clock framework basically disabled
all the unused fixed dividers, thus disabled a critical clock path for
the SCPI Co-Processor.

This patch simply sets the FCLK_DIV2 gate as critical to ensure
nobody can disable it.

Fixes: 05f814402d61 ("clk: meson: add fdiv clock gates")
Signed-off-by: Neil Armstrong <narmstrong@...libre.com>
---
 drivers/clk/meson/gxbb.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/clk/meson/gxbb.c b/drivers/clk/meson/gxbb.c
index b1e4d95..0e053c1 100644
--- a/drivers/clk/meson/gxbb.c
+++ b/drivers/clk/meson/gxbb.c
@@ -511,6 +511,7 @@ static struct clk_regmap gxbb_fclk_div2 = {
 		.ops = &clk_regmap_gate_ops,
 		.parent_names = (const char *[]){ "fclk_div2_div" },
 		.num_parents = 1,
+		.flags = CLK_IS_CRITICAL,
 	},
 };

-- 
2.7.4