[PATCH] MIPS: ath79: use correct fractional dividers for {CPU,DDR}_PLL on AR934x

[PATCH] MIPS: ath79: use correct fractional dividers for {CPU,DDR}_PLL on AR934x

[Gabor Juhos]

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(-)

diff --git a/arch/mips/ath79/clock.c b/arch/mips/ath79/clock.c
index b91ad3e..d272857 100644
--- a/arch/mips/ath79/clock.c
+++ b/arch/mips/ath79/clock.c
@@ -189,7 +189,7 @@ static void __init ar934x_clocks_init(void)
 	       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(void)
 	       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);
-- 
1.7.10

[PATCH] MIPS: ath79: use correct fractional dividers for {CPU,DDR}_PLL on AR934x

[Gabor Juhos]

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(-)

diff --git a/arch/mips/ath79/clock.c b/arch/mips/ath79/clock.c
index b91ad3e..d272857 100644
--- a/arch/mips/ath79/clock.c
+++ b/arch/mips/ath79/clock.c
@@ -189,7 +189,7 @@ static void __init ar934x_clocks_init(void)
 	       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(void)
 	       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);
-- 
1.7.10

Re: [PATCH] MIPS: ath79: use correct fractional dividers for {CPU,DDR}_PLL on AR934x

[Ralf Baechle]

Thanks, applied.

  Ralf