RE: [PATCH] clk: imx: add fractional-N pll support to pllv4

[Aisheng Dong]

> From: Aisheng Dong
> Sent: Monday, April 29, 2019 7:28 PM
> Subject: RE: [PATCH] clk: imx: add fractional-N pll support to pllv4
> > The pllv4 supports fractional-N function, the formula is:
> >
> > PLL output freq = input * (mult + num/denom),
> >
> > This patch adds fractional-N function support, including clock round
> > rate, calculate rate and set rate, with this patch, the clock rate of
> > APLL in clock tree is more accurate than before:
> >

BTW, one more question:
Does B0 chip support fractional for SPLL as this patch affects both APLL and SPLL?
I did not see NUM&DENOM register for SPLL in my doc, not sure if it's latest version.

Regards
Dong Aisheng

> > Without fraction:
> > apll_pre_sel                      1        1        1    24000000
> > 0     0  50000
> >    apll_pre_div                   1        1        2    24000000
> > 0     0  50000
> >       apll                        1        1        2   528000000
> > 0     0  50000
> >          apll_pfd3                0        0        0   792000000
> > 0     0  50000
> >          apll_pfd2                0        0        0   339428571
> > 0     0  50000
> >          apll_pfd1                0        0        0   352000000
> > 0     0  50000
> >             usdhc0                0        0        0
> 352000000
> > 0     0  50000
> >          apll_pfd0                1        1        1   352000000
> > 0     0  50000
> >
> > With fraction:
> > apll_pre_sel                      1        1        1    24000000
> > 0     0  50000
> >    apll_pre_div                   1        1        2    24000000
> > 0     0  50000
> >       apll                        1        1        2   529200000
> > 0     0  50000
> >          apll_pfd3                0        0        0   793800000
> > 0     0  50000
> >          apll_pfd2                0        0        0   340200000
> > 0     0  50000
> >          apll_pfd1                0        0        0   352800000
> > 0     0  50000
> >             usdhc0                0        0        0
> 352800000
> > 0     0  50000
> >          apll_pfd0                1        1        1   352800000
> > 0     0  50000
> >
> > Signed-off-by: Anson Huang <Anson.Huang@xxxxxxx>
> > ---
> >  drivers/clk/imx/clk-pllv4.c | 68
> > +++++++++++++++++++++++++++++++++++++++------
> >  1 file changed, 60 insertions(+), 8 deletions(-)
> >
> > diff --git a/drivers/clk/imx/clk-pllv4.c b/drivers/clk/imx/clk-pllv4.c
> > index d38bc9f..4ced5ca 100644
> > --- a/drivers/clk/imx/clk-pllv4.c
> > +++ b/drivers/clk/imx/clk-pllv4.c
> > @@ -64,13 +64,18 @@ static unsigned long clk_pllv4_recalc_rate(struct
> > clk_hw *hw,
> >  					   unsigned long parent_rate)
> >  {
> >  	struct clk_pllv4 *pll = to_clk_pllv4(hw);
> > -	u32 div;
> > +	u32 mult = readl_relaxed(pll->base + PLL_CFG_OFFSET);
> > +	u32 mfn = readl_relaxed(pll->base + PLL_NUM_OFFSET);
> > +	u32 mfd = readl_relaxed(pll->base + PLL_DENOM_OFFSET);
> 
> Nitpick:
> We usually don't write code like this.
> How about separate the assignment from declaration?
> 
> > +	u64 temp64 = parent_rate;
> >
> > -	div = readl_relaxed(pll->base + PLL_CFG_OFFSET);
> > -	div &= BM_PLL_MULT;
> > -	div >>= BP_PLL_MULT;
> > +	mult &= BM_PLL_MULT;
> > +	mult >>= BP_PLL_MULT;
> >
> > -	return parent_rate * div;
> > +	temp64 *= mfn;
> > +	do_div(temp64, mfd);
> > +
> > +	return (parent_rate * mult) + (u32)temp64;
> >  }
> >
> >  static long clk_pllv4_round_rate(struct clk_hw *hw, unsigned long
> > rate, @@
> > -78,14 +83,47 @@ static long clk_pllv4_round_rate(struct clk_hw *hw,
> > unsigned long rate,  {
> >  	unsigned long parent_rate = *prate;
> >  	unsigned long round_rate, i;
> > +	bool found = false;
> > +	u32 mfn, mfd = 1000000;
> > +	u32 max_mfd = 0x3FFFFFFF;
> 
> Please keep sort from long to short.
> And the multi Max_mfd definitions could be move out the function and
> Defined use macro.
> 
> > +	u64 temp64;
> >
> >  	for (i = 0; i < ARRAY_SIZE(pllv4_mult_table); i++) {
> >  		round_rate = parent_rate * pllv4_mult_table[i];
> > -		if (rate >= round_rate)
> > -			return round_rate;
> > +		if (rate >= round_rate) {
> > +			found = true;
> > +			break;
> > +		}
> > +	}
> > +
> > +	if (!found) {
> > +		pr_warn("%s: unable to round rate %lu, parent rate %lu\n",
> > +			clk_hw_get_name(hw), rate, parent_rate);
> > +		return 0;
> >  	}
> >
> > -	return round_rate;
> > +	if (parent_rate <= max_mfd)
> > +		mfd = parent_rate;
> > +
> > +	temp64 = (u64)(rate - round_rate);
> > +	temp64 *= mfd;
> > +	do_div(temp64, parent_rate);
> > +	mfn = temp64;
> > +
> > +	/*
> > +	 * NOTE: The value of numerator must always be configured to be
> > +	 * less than the value of the denominator. If we can't get a proper
> > +	 * pair of mfn/mfd, we simply return the round_rate without using
> > +	 * the frac part.
> > +	 */
> > +	if (mfn >= mfd)
> > +		return round_rate;
> > +
> > +	temp64 = (u64)parent_rate;
> > +	temp64 *= mfn;
> > +	do_div(temp64, mfd);
> > +
> > +	return round_rate + (u32)temp64;
> >  }
> >
> >  static bool clk_pllv4_is_valid_mult(unsigned int mult) @@ -106,17
> > +144,31 @@ static int clk_pllv4_set_rate(struct clk_hw *hw, unsigned long
> rate,  {
> >  	struct clk_pllv4 *pll = to_clk_pllv4(hw);
> >  	u32 val, mult;
> > +	u32 mfn, mfd = 1000000;
> > +	u32 max_mfd = 0x3FFFFFFF;
> 
> Ditto
> 
> Otherwise:
> Reviewed-by: Dong Aisheng <aisheng.dong@xxxxxxx>
> 
> Regards
> Dong Aisheng
> 
> > +	u64 temp64;
> >
> >  	mult = rate / parent_rate;
> >
> >  	if (!clk_pllv4_is_valid_mult(mult))
> >  		return -EINVAL;
> >
> > +	if (parent_rate <= max_mfd)
> > +		mfd = parent_rate;
> > +
> > +	temp64 = (u64)(rate - mult * parent_rate);
> > +	temp64 *= mfd;
> > +	do_div(temp64, parent_rate);
> > +	mfn = temp64;
> > +
> >  	val = readl_relaxed(pll->base + PLL_CFG_OFFSET);
> >  	val &= ~BM_PLL_MULT;
> >  	val |= mult << BP_PLL_MULT;
> >  	writel_relaxed(val, pll->base + PLL_CFG_OFFSET);
> >
> > +	writel_relaxed(mfn, pll->base + PLL_NUM_OFFSET);
> > +	writel_relaxed(mfd, pll->base + PLL_DENOM_OFFSET);
> > +
> >  	return 0;
> >  }
> >
> > --
> > 2.7.4