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From: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
To: linux-amlogic@lists.infradead.org, linux-clk@vger.kernel.org,
	jbrunet@baylibre.com, narmstrong@baylibre.com
Cc: linux-arm-kernel@lists.infradead.org,
	linux-kernel@vger.kernel.org, mturquette@baylibre.com,
	sboyd@kernel.org,
	Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Subject: [RFC v1 2/7] clk: meson: meson8b: do not use cpu_div3 for cpu_scale_out_sel
Date: Wed, 14 Nov 2018 23:57:20 +0100	[thread overview]
Message-ID: <20181114225725.2821-3-martin.blumenstingl@googlemail.com> (raw)
In-Reply-To: <20181114225725.2821-1-martin.blumenstingl@googlemail.com>

The cpu_div3 clock (cpu_in divided by 3) generates a signal with a duty
cycle of 33%. The CPU clock however requires a clock signal with a duty
cycle of 50% to run stable.
cpu_div3 was observed to be problematic when cycling through all
available CPU frequencies (with additional patches on top of this one)
while running "stress --cpu 4" in the background. This caused sporadic
hangs where the whole system would fully lock up.

Amlogic's 3.10 kernel code also does not use the cpu_div3 clock either
when changing the CPU clock.

Signed-off-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
---
 drivers/clk/meson/meson8b.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/drivers/clk/meson/meson8b.c b/drivers/clk/meson/meson8b.c
index 40e77fe4ba7c..8a3c346e110d 100644
--- a/drivers/clk/meson/meson8b.c
+++ b/drivers/clk/meson/meson8b.c
@@ -608,20 +608,27 @@ static struct clk_regmap meson8b_cpu_scale_div = {
 	},
 };
 
+static u32 mux_table_cpu_scale_out_sel[] = { 0, 1, 3 };
 static struct clk_regmap meson8b_cpu_scale_out_sel = {
 	.data = &(struct clk_regmap_mux_data){
 		.offset = HHI_SYS_CPU_CLK_CNTL0,
 		.mask = 0x3,
 		.shift = 2,
+		.table = mux_table_cpu_scale_out_sel,
 	},
 	.hw.init = &(struct clk_init_data){
 		.name = "cpu_scale_out_sel",
 		.ops = &clk_regmap_mux_ro_ops,
+		/*
+		 * NOTE: We are skipping the parent with value 0x2 (which is
+		 * "cpu_div3") because it results in a duty cycle of 33% which
+		 * makes the system unstable and can result in a lockup of the
+		 * whole system.
+		 */
 		.parent_names = (const char *[]) { "cpu_in_sel",
 						   "cpu_div2",
-						   "cpu_div3",
 						   "cpu_scale_div" },
-		.num_parents = 4,
+		.num_parents = 3,
 		.flags = CLK_SET_RATE_PARENT,
 	},
 };
-- 
2.19.1


  parent reply	other threads:[~2018-11-14 22:57 UTC|newest]

Thread overview: 16+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-11-14 22:57 [RFC v1 0/7] Meson8b: make the CPU clock mutable Martin Blumenstingl
2018-11-14 22:57 ` [RFC v1 1/7] clk: meson: meson8b: run from the XTAL when changing the CPU frequency Martin Blumenstingl
2018-11-15  9:53   ` Jerome Brunet
2018-11-14 22:57 ` Martin Blumenstingl [this message]
2018-11-15  9:42   ` [RFC v1 2/7] clk: meson: meson8b: do not use cpu_div3 for cpu_scale_out_sel Jerome Brunet
2018-11-14 22:57 ` [RFC v1 3/7] clk: meson: clk-pll: check if the clock is already enabled Martin Blumenstingl
2018-11-15  9:14   ` Jerome Brunet
2018-11-14 22:57 ` [RFC v1 4/7] clk: meson: clk-pll: add the is_enabled function in the clk_ops Martin Blumenstingl
2018-11-15  9:16   ` Jerome Brunet
2018-11-14 22:57 ` [RFC v1 5/7] clk: meson: meson8b: mark the CPU clock as CLK_IS_CRITICAL Martin Blumenstingl
2018-11-15  9:46   ` Jerome Brunet
2018-11-14 22:57 ` [RFC v1 6/7] clk: meson: meson8b: add support for more M/N values in sys_pll Martin Blumenstingl
2018-11-15  9:41   ` Jerome Brunet
2018-11-14 22:57 ` [RFC v1 7/7] clk: meson: meson8b: allow changing the CPU clock tree Martin Blumenstingl
2018-11-15  9:46   ` Jerome Brunet
2018-11-15 10:08 ` [RFC v1 0/7] Meson8b: make the CPU clock mutable Neil Armstrong

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