linux-kernel - Re: [PATCH V5 4/5] phy: freescale: fsl-samsung-hdmi: Use closest divider

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Message-ID: <0a860fc7-14df-40c6-a92a-868568ae7a24@kontron.de>
Date: Wed, 4 Sep 2024 15:40:33 +0200
From: Frieder Schrempf <frieder.schrempf@...tron.de>
To: Adam Ford <aford173@...il.com>, linux-phy@...ts.infradead.org
Cc: dominique.martinet@...ark-techno.com, linux-imx@....com,
 festevam@...il.com, aford@...conembedded.com, Sandor.yu@....com,
 Vinod Koul <vkoul@...nel.org>, Kishon Vijay Abraham I <kishon@...nel.org>,
 Marco Felsch <m.felsch@...gutronix.de>,
 Uwe Kleine-König <u.kleine-koenig@...gutronix.de>,
 Lucas Stach <l.stach@...gutronix.de>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH V5 4/5] phy: freescale: fsl-samsung-hdmi: Use closest
 divider

On 04.09.24 4:32 AM, Adam Ford wrote:
> Currently, if the clock values cannot be set to the exact rate,
> the round_rate and set_rate functions use the closest value found in
> the look-up-table.  In preparation of removing values from the LUT
> that can be calculated evenly with the integer calculator, it's
> necessary to ensure to check both the look-up-table and the integer
> divider clock values to get the closest values to the requested
> value.  It does this by measuring the difference between the
> requested clock value and the closest value in both integer divider
> calucator and the fractional clock look-up-table.
> 
> Which ever has the smallest difference between them is returned as
> the cloesest rate.
> 
> Signed-off-by: Adam Ford <aford173@...il.com>
> Signed-off-by: Dominique Martinet <dominique.martinet@...ark-techno.com>
> ---
> V5:  No Change
> V4:  New to series
> ---
>  drivers/phy/freescale/phy-fsl-samsung-hdmi.c | 40 +++++++++++++++-----
>  1 file changed, 31 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/phy/freescale/phy-fsl-samsung-hdmi.c b/drivers/phy/freescale/phy-fsl-samsung-hdmi.c
> index 8f2c0082aa12..56b08e684179 100644
> --- a/drivers/phy/freescale/phy-fsl-samsung-hdmi.c
> +++ b/drivers/phy/freescale/phy-fsl-samsung-hdmi.c
> @@ -550,7 +550,7 @@ static unsigned long phy_clk_recalc_rate(struct clk_hw *hw,
>  static long phy_clk_round_rate(struct clk_hw *hw,
>  			       unsigned long rate, unsigned long *parent_rate)
>  {
> -	u32 int_div_clk;
> +	u32 int_div_clk, delta_int, delta_frac;
>  	int i;
>  	u16 m;
>  	u8 p, s;
> @@ -563,6 +563,7 @@ static long phy_clk_round_rate(struct clk_hw *hw,
>  	for (i = ARRAY_SIZE(phy_pll_cfg) - 1; i >= 0; i--)
>  		if (phy_pll_cfg[i].pixclk <= rate)
>  			break;
> +
>  	/* If the rate is an exact match, return it now */
>  	if (rate == phy_pll_cfg[i].pixclk)
>  		return phy_pll_cfg[i].pixclk;
> @@ -579,15 +580,21 @@ static long phy_clk_round_rate(struct clk_hw *hw,
>  	if (int_div_clk == rate)
>  		return int_div_clk;
>  
> -	/* Fall back to the closest value in the LUT */
> -	return phy_pll_cfg[i].pixclk;
> +	/* Calculate the differences and use the closest one */
> +	delta_frac = (rate - phy_pll_cfg[i].pixclk);
> +	delta_int = (rate - int_div_clk);
> +
> +	if (delta_int < delta_frac)
> +		return int_div_clk;
> +	else
> +		return phy_pll_cfg[i].pixclk;
>  }
>  
>  static int phy_clk_set_rate(struct clk_hw *hw,
>  			    unsigned long rate, unsigned long parent_rate)
>  {
>  	struct fsl_samsung_hdmi_phy *phy = to_fsl_samsung_hdmi_phy(hw);
> -	u32 int_div_clk;
> +	u32 int_div_clk, delta_int, delta_frac;
>  	int i;
>  	u16 m;
>  	u8 p, s;
> @@ -602,19 +609,34 @@ static int phy_clk_set_rate(struct clk_hw *hw,
>  		calculated_phy_pll_cfg.pll_div_regs[2] = FIELD_PREP(REG03_PMS_S_MASK, s-1);
>  		/* pll_div_regs 3-6 are fixed and pre-defined already */
>  		phy->cur_cfg  = &calculated_phy_pll_cfg;

                             ^ unneeded whitespace (comment belongs to
patch 3/5)

> +		goto done;
>  	} else {
>  		/* Otherwise, search the LUT */
> -		dev_dbg(phy->dev, "fsl_samsung_hdmi_phy: using fractional divider\n");
> -		for (i = ARRAY_SIZE(phy_pll_cfg) - 1; i >= 0; i--)
> -			if (phy_pll_cfg[i].pixclk <= rate)
> +		for (i = ARRAY_SIZE(phy_pll_cfg) - 1; i >= 0; i--) {
> +			if (phy_pll_cfg[i].pixclk == rate) {
> +				dev_dbg(phy->dev, "fsl_samsung_hdmi_phy: using fractional divider\n");
> +				phy->cur_cfg = &phy_pll_cfg[i];
> +				goto done;
> +			}
> +
> +			if (phy_pll_cfg[i].pixclk < rate)
>  				break;
> +		}
>  
>  		if (i < 0)
>  			return -EINVAL;
> -
> -		phy->cur_cfg = &phy_pll_cfg[i];
>  	}
>  
> +	/* Calculate the differences for each clock against the requested value */
> +	delta_frac = (rate - phy_pll_cfg[i].pixclk);
> +	delta_int = (rate - int_div_clk);
> +
> +	/* Use the value closest to the desired */
> +	if (delta_int < delta_frac)
> +		phy->cur_cfg  = &calculated_phy_pll_cfg;

                             ^ unneeded whitespace

Are you sure that this is correct? The calculated_phy_pll_cfg is only
set above if there is an exact match for the integer divider. I don't
think it contains the data you expect here, or am I missing something?

> +	else
> +		phy->cur_cfg = &phy_pll_cfg[i];
> +done:
>  	return fsl_samsung_hdmi_phy_configure(phy, phy->cur_cfg);
>  }
>