linux-kernel - Re: [PATCH] phy: freescale: fsl-samsung-hdmi: return closest rate instead LUT

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Message-ID: <638865e3-53ea-44a4-a541-ed73ee2c476f@kontron.de>
Date: Mon, 10 Mar 2025 10:32:42 +0100
From: Frieder Schrempf <frieder.schrempf@...tron.de>
To: Dominique Martinet <dominique.martinet@...ark-techno.com>,
 Vinod Koul <vkoul@...nel.org>, Kishon Vijay Abraham I <kishon@...nel.org>
Cc: Adam Ford <aford173@...il.com>, Marco Felsch <m.felsch@...gutronix.de>,
 Uwe Kleine-König <u.kleine-koenig@...libre.com>,
 Lucas Stach <l.stach@...gutronix.de>, linux-phy@...ts.infradead.org,
 linux-kernel@...r.kernel.org, Makoto Sato <makoto.sato@...ark-techno.com>
Subject: Re: [PATCH] phy: freescale: fsl-samsung-hdmi: return closest rate
 instead LUT

On 10.03.25 2:21 AM, Dominique Martinet wrote:
> From: Makoto Sato <makoto.sato@...ark-techno.com>
> 
> If the requested rate is not an exact match of the integer divider
> phy_clk_round_rate() would return the look up table value,
> but phy_clk_set_rate() can still use the integer divider if it results
> in a frequency that is closer than the look up table.
> 
> In particular, not returning the actually used value here made the hdmi
> bridge driver reject a frequency that has an integer divider rate
> within 0.5% of the target:
> for 83.5mHz, the integer divider generates 83.2mHz (-0.36%), but the
> next LUT value (82.5mHz) is 1.2% off which incorrectly rejects modes
> requiring this frequency.
> 
> This commit updates phy_clk_round_rate() to use the same logic as the
> set operation.
> 
> Signed-off-by: Makoto Sato <makoto.sato@...ark-techno.com>
> Signed-off-by: Dominique Martinet <dominique.martinet@...ark-techno.com>

This looks good to me.

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

But I think we should also add the following Fixes tag:

Fixes: 058ea4a06704 ("phy: freescale: fsl-samsung-hdmi: Use closest
divider")

> ---
> We're finally using this rewrite in our (outdated) tree and noticed the
> "best" mode missing on one of our picky displays.
> It all looks good with this fix, thanks again!
> ---
>  drivers/phy/freescale/phy-fsl-samsung-hdmi.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/phy/freescale/phy-fsl-samsung-hdmi.c b/drivers/phy/freescale/phy-fsl-samsung-hdmi.c
> index e4c0a82d16d9ef0f64ebf9e505b8620423cdc416..91c4d27a31f48fc49f1e8417d7089f5519b8a0a2 100644
> --- a/drivers/phy/freescale/phy-fsl-samsung-hdmi.c
> +++ b/drivers/phy/freescale/phy-fsl-samsung-hdmi.c
> @@ -557,8 +557,9 @@ static long phy_clk_round_rate(struct clk_hw *hw,
>  	if (int_div_clk == rate)
>  		return int_div_clk;
>  
> -	/* If neither rate is an exact match, use the value from the LUT */
> -	return fract_div_phy->pixclk;
> +	/* If neither rate is an exact match, use the closest value */
> +	return fsl_samsung_hdmi_phy_get_closest_rate(rate, int_div_clk,
> +						     fract_div_phy->pixclk);
>  }
>  
>  static int phy_use_fract_div(struct fsl_samsung_hdmi_phy *phy, const struct phy_config *fract_div_phy)
> 
> ---
> base-commit: 80e54e84911a923c40d7bee33a34c1b4be148d7a
> change-id: 20250310-8ulp_hdmi-f8deac08611e
> 
> Best regards,