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ar71xx: use correct fractional dividers for {CPU,DDR}_PLL on AR934x

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SVN-Revision: 33318
This commit is contained in:
Gabor Juhos 2012-09-05 19:26:50 +00:00
parent 81bb246a8d
commit 069f544d2b
1 changed files with 49 additions and 0 deletions
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target/linux/ar71xx/patches-3.3/136-MIPS-ath79-use-correct-fractional-dividers-for-CPU-D.patch Normal file
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From 7328ff547389ee0b455cbf98bdfc819731d9f7b9 Mon Sep 17 00:00:00 2001
From: Gabor Juhos <juhosg@openwrt.org>
Date: Fri, 31 Aug 2012 14:22:35 +0200
Subject: [PATCH] MIPS: ath79: use correct fractional dividers for
{CPU,DDR}_PLL on AR934x
The current dividers in the code are wrong and this
leads to broken CPU frequency calculation on boards
where the fractional part is used.
For example, if the SoC is running from a 40MHz
reference clock, refdiv=1, nint=14, outdiv=0 and
nfrac=31 the real frequency is 579.375MHz but the
current code calculates 569.687MHz instead.
Because the system time is indirectly related to
the CPU frequency the broken computation causes
drift in the system time.
The correct divider is 2^6 for the CPU PLL and 2^10
for the DDR PLL. Use the correct values to fix the
issue.
Cc: <stable@vger.kernel.org> [3.5+]
Signed-off-by: Gabor Juhos <juhosg@openwrt.org>
---
arch/mips/ath79/clock.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
--- a/arch/mips/ath79/clock.c
+++ b/arch/mips/ath79/clock.c
@@ -189,7 +189,7 @@ static void __init ar934x_clocks_init(vo
AR934X_PLL_CPU_CONFIG_NFRAC_MASK;
cpu_pll = nint * ath79_ref_clk.rate / ref_div;
- cpu_pll += frac * ath79_ref_clk.rate / (ref_div * (2 << 6));
+ cpu_pll += frac * ath79_ref_clk.rate / (ref_div * (1 << 6));
cpu_pll /= (1 << out_div);
pll = ath79_pll_rr(AR934X_PLL_DDR_CONFIG_REG);
@@ -203,7 +203,7 @@ static void __init ar934x_clocks_init(vo
AR934X_PLL_DDR_CONFIG_NFRAC_MASK;
ddr_pll = nint * ath79_ref_clk.rate / ref_div;
- ddr_pll += frac * ath79_ref_clk.rate / (ref_div * (2 << 10));
+ ddr_pll += frac * ath79_ref_clk.rate / (ref_div * (1 << 10));
ddr_pll /= (1 << out_div);
clk_ctrl = ath79_pll_rr(AR934X_PLL_CPU_DDR_CLK_CTRL_REG);