[PATCH V4] ARM: imx: correct Audio/Video PLL rate calculation formula

[Lothar Waßmann]

Hi,

> The audio/video PLL's rate calculation formula is as below in RM:
> 
> Fref * (DIV_SELECT + NUM / DENOM),
> 
> in original 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
> calculation formula should be better used instead:
> 
> (parent_rate * div) + ((parent_rate * mfn) / mfd)
> 
> and we also need to consider parent_rate * mfd may exceed
> a 32 bit value, 64 bit value should be used.
> 
> Below is one example of old/new formula's difference:
> 
> On i.MX7D, DRAM PLL is a Audio/Video type PLL, the target freq
> is 1066MHz, the register settings are as below:
> 
> PLL_DDRn: 8060202C   -> div = 0x2C
> DDR_NUM: 06AAAC4D    -> mfn = 0x6AAAC4D
> DDR_DENOM: 100003EC  -> mfd = 0x100003EC
> 
> parent_rate = 24MHz.
> 
> with old formula, the (parent_rate / mfd) * mfn = 0, with new formula,
> the (parent_rate * mfn) / mfd = 10MHz, so old formula gets
> PLL_DDR = 1056MHz, while the updated formula gets PLL_DDR = 1066MHz
> which exactly matches the real rate.
> 
> Signed-off-by: Anson Huang <b20788 at freescale.com>
> ---
>  drivers/clk/imx/clk-pllv3.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/clk/imx/clk-pllv3.c b/drivers/clk/imx/clk-pllv3.c
> index 641ebc5..e34a925 100644
> --- a/drivers/clk/imx/clk-pllv3.c
> +++ b/drivers/clk/imx/clk-pllv3.c
> @@ -203,8 +203,13 @@ 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 = parent_rate;
> +
> +	temp64 *= mfn;
> +	do_div(temp64, mfd);
> +
> +	return (parent_rate * div) + temp64;
>  
> -	return (parent_rate * div) + ((parent_rate / mfd) * mfn);
>  }
>  
>  static long clk_pllv3_av_round_rate(struct clk_hw *hw, unsigned long rate,
>
What about clk_pllv3_av_round_rate() which also has:
|	return parent_rate * div + parent_rate / mfd * mfn;
as already stated in: <20150507092136.0f3f583a at ipc1.ka-ro>


Lothar Waßmann
-- 
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