linux-kernel - [PATCH 0/1] clk: meson: fix PLL rate rounding

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Date:   Sun, 24 Mar 2019 17:43:26 +0100
From:   Martin Blumenstingl <martin.blumenstingl@...glemail.com>
To:     narmstrong@...libre.com, jbrunet@...libre.com,
        linux-amlogic@...ts.infradead.org, linux-clk@...r.kernel.org
Cc:     mturquette@...libre.com, sboyd@...nel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Martin Blumenstingl <martin.blumenstingl@...glemail.com>
Subject: [PATCH 0/1] clk: meson: fix PLL rate rounding

Hi Jerome,

can you please look at this small fix? I discovered that my Odroid-C1
wasn't booting anymore. My other Meson8m2 board was using fine.

While investigating this I found that it hangs while setting the
sys_pll_dco rate. This is important because unlike Odroid-C1 my
Meson8m2 board has a fixed regulator (and thus always runs at a
fixed CPU speed).
It always hanged while trying to set a CPU frequency of 312MHz. This
can be achieved with:
  24MHz (xtal) * 52 (m) / 1 (n) / 4 (sys_pll)
However, my added debug logging showed that it was trying to set an
M value of 51, resulting in an output frequency of 306MHz. My debug
logs showed that meson_clk_get_pll_settings() considers 1248MHz
(which is the rate requested for sys_pll_dco for a CPU frequency of
 312MHz) "worse" than 1224MHz.

I'm not sure exactly why the bug caused the board to hang, but my
patch fixes it.

Please apply this to v5.1-rc as I believe the Odroid-C1 on kernelci
also suffers from this issue.

Martin Blumenstingl (1):
  clk: meson: pll: fix rounding and setting a rate that matches
    precisely

 drivers/clk/meson/clk-pll.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

-- 
2.21.0