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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 6/7] clk: meson: meson8b: add support for more M/N values in sys_pll
Date: Wed, 14 Nov 2018 23:57:24 +0100	[thread overview]
Message-ID: <20181114225725.2821-7-martin.blumenstingl@googlemail.com> (raw)
In-Reply-To: <20181114225725.2821-1-martin.blumenstingl@googlemail.com>

The sys_pll on the EC-100 board is configured to 1584MHz at boot
(either by u-boot, firmware or chip defaults). This is achieved by using
M = 66, N = 1 (24MHz * 66 / 1).
At boot the CPU clock is running off sys_pll divided by 2 which results
in 792MHz. Thus M = 66 is considered to be a "safe" value for Meson8b.

To achieve 1608MHz (one of the CPU OPPs on Meson8 and Meson8m2) we need
M = 67, N = 1. I ran "stress --cpu 4" while infinitely cycling through
all available frequencies on my Meson8m2 board and could not spot any
issues with this setting (after ~12 hours of running this).

On Meson8, Meson8b and Meson8m2 we also want to be able to use 408MHz
and 816MHz CPU frequencies. These can be achieved by dividing sys_pll by
4 (for 408MHz) or 2 (for 816MHz). That means that sys_pll has to run at
1632MHz which can be generated using M = 68, N = 1.
Similarily we also want to be able to use 1008MHz as CPU frequency. This
means that sys_pll has to run either at 1008MHz or 2016MHz. The former
would result in an M value of 42, which is lower than the smallest value
used by the 3.10 GPL kernel sources from Amlogic (50 is the lower limit
there). Thus we need to run sys_pll at 2016MHz which can ge generated
using M = 84, N = 1.
I tested M = 68 and M = 84 on my Meson8b Odroid-C1 and my Meson8m2 board
by running "stress --cpu 4" while infinitely cycling thorugh all
available frequencies. I could not spot any issues after ~12 hours of
running this.

Amlogic's 3.10 GPL kernel sources have more M/N combinations. I did not
add them yet because M = 74 (to achieve close to 1800MHz on Meson8) and
M = 82 (to achieve close to 1992MHz on Meson8 as well) caused my
Meson8m2 board to hang randomly. It's not clear why this is (for example
because the board's voltage regulator design is bad, some missing bits
for these values in our clk-pll driver, etc.). Thus the following M
values from the Amlogic 3.10 GPL kernel sources are skipped as of now:
69, 70, 71, 72, 73, 74, 76, 78, 80, 82, 84, 86, 88, 90, 92, 94, 96, 98

Signed-off-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
---
 drivers/clk/meson/meson8b.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/clk/meson/meson8b.c b/drivers/clk/meson/meson8b.c
index d566dd5bc567..c06a1a7faa4c 100644
--- a/drivers/clk/meson/meson8b.c
+++ b/drivers/clk/meson/meson8b.c
@@ -43,6 +43,11 @@ static const struct pll_params_table sys_pll_params_table[] = {
 	PLL_PARAMS(62, 1),
 	PLL_PARAMS(63, 1),
 	PLL_PARAMS(64, 1),
+	PLL_PARAMS(65, 1),
+	PLL_PARAMS(66, 1),
+	PLL_PARAMS(67, 1),
+	PLL_PARAMS(68, 1),
+	PLL_PARAMS(84, 1),
 	{ /* sentinel */ },
 };
 
-- 
2.19.1


  parent reply	other threads:[~2018-11-14 22:58 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 ` [RFC v1 2/7] clk: meson: meson8b: do not use cpu_div3 for cpu_scale_out_sel Martin Blumenstingl
2018-11-15  9:42   ` 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 ` Martin Blumenstingl [this message]
2018-11-15  9:41   ` [RFC v1 6/7] clk: meson: meson8b: add support for more M/N values in sys_pll 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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