linux-kernel - Re: [PATCH 3/3] phy: freescale: fsl-samsung-hdmi: Clean up fld_tg

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Message-ID: <379853e6-bb96-4556-82b8-27ed49f974b8@kontron.de>
Date: Tue, 22 Oct 2024 09:16:12 +0200
From: Frieder Schrempf <frieder.schrempf@...tron.de>
To: Adam Ford <aford173@...il.com>, linux-phy@...ts.infradead.org
Cc: aford@...conembedded.com, sandor.yu@....com, Vinod Koul
 <vkoul@...nel.org>, Kishon Vijay Abraham I <kishon@...nel.org>,
 Dominique Martinet <dominique.martinet@...ark-techno.com>,
 Marco Felsch <m.felsch@...gutronix.de>,
 Uwe Kleine-König <u.kleine-koenig@...libre.com>,
 Lucas Stach <l.stach@...gutronix.de>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/3] phy: freescale: fsl-samsung-hdmi: Clean up
 fld_tg_code calculation

On 20.10.24 6:50 PM, Adam Ford wrote:
> Currently, the calcuation for fld_tg_code is based on a lookup table,
> but there are gaps in the lookup table, and frequencies in these
> gaps may not properly use the correct divider.  Based on the description
> of FLD_CK_DIV, the internal PLL frequency should be less than 50 MHz,
> so directly calcuate the value of FLD_CK_DIV from pixclk.
> This allow for proper calcuation of any pixel clock and eliminates a
> few gaps in the LUT.
> 
> Since the value of the int_pllclk is in Hz, do the fixed-point
> math in Hz to achieve a more accurate value and reduces the complexity
> of the caluation to 24MHz * (256 / int_pllclk).
> 
> Fixes: 6ad082bee902 ("phy: freescale: add Samsung HDMI PHY")
> Signed-off-by: Adam Ford <aford173@...il.com>

Reviewed-by: Frieder Schrempf <frieder.schrempf@...tron.de>

> ---
>  drivers/phy/freescale/phy-fsl-samsung-hdmi.c | 32 +++++++-------------
>  1 file changed, 11 insertions(+), 21 deletions(-)
> 
> diff --git a/drivers/phy/freescale/phy-fsl-samsung-hdmi.c b/drivers/phy/freescale/phy-fsl-samsung-hdmi.c
> index 719f8972cb5a..0bfe0c0907a0 100644
> --- a/drivers/phy/freescale/phy-fsl-samsung-hdmi.c
> +++ b/drivers/phy/freescale/phy-fsl-samsung-hdmi.c
> @@ -331,25 +331,17 @@ fsl_samsung_hdmi_phy_configure_pll_lock_det(struct fsl_samsung_hdmi_phy *phy,
>  {
>  	u32 pclk = cfg->pixclk;
>  	u32 fld_tg_code;
> -	u32 pclk_khz;
> -	u8 div = 1;
> -
> -	switch (cfg->pixclk) {
> -	case  22250000 ...  47500000:
> -		div = 1;
> -		break;
> -	case  50349650 ...  99000000:
> -		div = 2;
> -		break;
> -	case 100699300 ... 198000000:
> -		div = 4;
> -		break;
> -	case 205000000 ... 297000000:
> -		div = 8;
> -		break;
> +	u32 int_pllclk;
> +	u8 div;
> +
> +	/* Find int_pllclk speed */
> +	for (div = 0; div < 4; div++) {
> +		int_pllclk = pclk / (1 << div);
> +		if (int_pllclk < (50 * MHZ))
> +			break;
>  	}
>  
> -	writeb(FIELD_PREP(REG12_CK_DIV_MASK, ilog2(div)), phy->regs + PHY_REG(12));
> +	writeb(FIELD_PREP(REG12_CK_DIV_MASK, div), phy->regs + PHY_REG(12));
>  
>  	/*
>  	 * Calculation for the frequency lock detector target code (fld_tg_code)
> @@ -362,10 +354,8 @@ fsl_samsung_hdmi_phy_configure_pll_lock_det(struct fsl_samsung_hdmi_phy *phy,
>  	 *        settings rounding up always too. TODO: Check if that is
>  	 *        correct.
>  	 */
> -	pclk /= div;
> -	pclk_khz = pclk / 1000;
> -	fld_tg_code = 256 * 1000 * 1000 / pclk_khz * 24;
> -	fld_tg_code = DIV_ROUND_UP(fld_tg_code, 1000);
> +
> +	fld_tg_code =  DIV_ROUND_UP(24 * MHZ * 256, int_pllclk);
>  
>  	/* FLD_TOL and FLD_RP_CODE taken from downstream driver */
>  	writeb(FIELD_PREP(REG13_TG_CODE_LOW_MASK, fld_tg_code),