[PATCH 02/11] clk: imx: correct AV PLL rate formula

Dong Aisheng
2016-06-08T14:55:01Z

From: Anson Huang <b20788@freescale.com>

The audio/video PLL's rate calculation is as below in RM:

Fref * (DIV_SELECT + NUM / DENOM), in origin clk-pllv3's
code, below code is used:

(parent_rate * div) + ((parent_rate / mfd) * mfn

as it does NOT consider the float data using div, so below
formula should be used as a decent method:

(parent_rate * div) + ((parent_rate * mfn) / mfd)

and we also need to consider parent_rate * mfd may overflow
a 32 bit value, 64 bit value should be used.

After updating this formula, the dram PLL's rate is
1066MHz, which is correct, while the old formula gets
1056MHz.

[Aisheng: fix clk_pllv3_av_round_rate too]

Signed-off-by: Anson Huang <b20788@freescale.com>
Signed-off-by: Dong Aisheng <aisheng.dong@nxp.com>
---
drivers/clk/imx/clk-pllv3.c | 8 ++++++--
1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/drivers/clk/imx/clk-pllv3.c b/drivers/clk/imx/clk-pllv3.c
index 44d294a336f0..eea2b1b3791e 100644
--- a/drivers/clk/imx/clk-pllv3.c
+++ b/drivers/clk/imx/clk-pllv3.c
@@ -218,8 +218,12 @@ static unsigned long clk_pllv3_av_recalc_rate(struct clk_hw *hw,
u32 mfn = readl_relaxed(pll->base + PLL_NUM_OFFSET);
u32 mfd = readl_relaxed(pll->base + PLL_DENOM_OFFSET);
u32 div = readl_relaxed(pll->base) & pll->div_mask;
+ u64 temp64 = (u64)parent_rate;

- return (parent_rate * div) + ((parent_rate / mfd) * mfn);
+ temp64 *= mfn;
+ do_div(temp64, mfd);
+
+ return (parent_rate * div) + (u32)temp64;
}

static long clk_pllv3_av_round_rate(struct clk_hw *hw, unsigned long rate,
@@ -243,7 +247,7 @@ static long clk_pllv3_av_round_rate(struct clk_hw *hw, unsigned long rate,
do_div(temp64, parent_rate);
mfn = temp64;

- return parent_rate * div + parent_rate / mfd * mfn;
+ return parent_rate * div + parent_rate * mfn / mfd;
}

static int clk_pllv3_av_set_rate(struct clk_hw *hw, unsigned long rate,
--
1.9.1