linux-kernel - Re: [PATCH] clk: imx: composite-8m: Add imx8m_divider_determine

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Message-ID: <ZIbdrLyBUwtgY2HE@linaro.org>
Date:   Mon, 12 Jun 2023 11:56:12 +0300
From:   Abel Vesa <abel.vesa@...aro.org>
To:     Adam Ford <aford173@...il.com>
Cc:     linux-clk@...r.kernel.org, aford@...conembedded.com,
        Abel Vesa <abelvesa@...nel.org>, Peng Fan <peng.fan@....com>,
        Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>,
        Shawn Guo <shawnguo@...nel.org>,
        Sascha Hauer <s.hauer@...gutronix.de>,
        Pengutronix Kernel Team <kernel@...gutronix.de>,
        Fabio Estevam <festevam@...il.com>,
        NXP Linux Team <linux-imx@....com>,
        "moderated list:ARM/FREESCALE IMX / MXC ARM ARCHITECTURE" 
        <linux-arm-kernel@...ts.infradead.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] clk: imx: composite-8m: Add imx8m_divider_determine_rate

On 23-05-06 14:53:25, Adam Ford wrote:
> Currently, certain clocks are derrived as a divider from their
> parent clock.  For some clocks, even when CLK_SET_RATE_PARENT
> is set, the parent clock is not properly set which can lead
> to some relatively inaccurate clock values.
> 
> Unlike imx/clk-composite-93 and imx/clk-divider-gate, it
> cannot rely on calling a standard determine_rate function,
> because the 8m composite clocks have a pre-divider and
> post-divider. Because of this, a custom determine_rate
> function is necessary to determine the maximum clock
> division which is equivalent to pre-divider * the
> post-divider.
> 
> With this added, the system can attempt to adjust the parent rate
> when the proper flags are set which can lead to a more precise clock
> value.
> 
> On the imx8mplus, no clock changes are present.
> On the Mini and Nano, this can help achieve more accurate
> lcdif clocks. When trying to get a pixel clock of 31.500MHz
> on an imx8m Nano, the clocks divided the 594MHz down, but
> left the parent rate untouched which caused a calulation error.
> 
> Before:
> video_pll              594000000
>   video_pll_bypass     594000000
>     video_pll_out      594000000
>       disp_pixel       31263158
>         disp_pixel_clk 31263158
> 
> Variance = -236842 Hz
> 
> After this patch:
> video_pll               31500000
>   video_pll_bypass      31500000
>     video_pll_out       31500000
>       disp_pixel        31500000
>         disp_pixel_clk  31500000
> 
> Variance = 0 Hz
> 
> All other clocks rates and parent were the same.
> Similar results on imx8mm were found.
> 
> Fixes: 690dccc4a0bf ("Revert "clk: imx: composite-8m: Add support to determine_rate"")
> Signed-off-by: Adam Ford <aford173@...il.com>

Reviewed-by: Abel Vesa <abel.vesa@...aro.org>

> ---
> V2:  Fix build warning found by build bot and fix prediv_value
>      and div_value because the values stored are the divisor - 1,
>      so we need to add 1 to the values to be correct.
> 
> diff --git a/drivers/clk/imx/clk-composite-8m.c b/drivers/clk/imx/clk-composite-8m.c
> index cbf0d7955a00..7a6e3ce97133 100644
> --- a/drivers/clk/imx/clk-composite-8m.c
> +++ b/drivers/clk/imx/clk-composite-8m.c
> @@ -119,10 +119,41 @@ static int imx8m_clk_composite_divider_set_rate(struct clk_hw *hw,
>  	return ret;
>  }
>  
> +static int imx8m_divider_determine_rate(struct clk_hw *hw,
> +				      struct clk_rate_request *req)
> +{
> +	struct clk_divider *divider = to_clk_divider(hw);
> +	int prediv_value;
> +	int div_value;
> +
> +	/* if read only, just return current value */
> +	if (divider->flags & CLK_DIVIDER_READ_ONLY) {
> +		u32 val;
> +
> +		val = readl(divider->reg);
> +		prediv_value = val >> divider->shift;
> +		prediv_value &= clk_div_mask(divider->width);
> +		prediv_value++;
> +
> +		div_value = val >> PCG_DIV_SHIFT;
> +		div_value &= clk_div_mask(PCG_DIV_WIDTH);
> +		div_value++;
> +
> +		return divider_ro_determine_rate(hw, req, divider->table,
> +						 PCG_PREDIV_WIDTH + PCG_DIV_WIDTH,
> +						 divider->flags, prediv_value * div_value);
> +	}
> +
> +	return divider_determine_rate(hw, req, divider->table,
> +				      PCG_PREDIV_WIDTH + PCG_DIV_WIDTH,
> +				      divider->flags);
> +}
> +
>  static const struct clk_ops imx8m_clk_composite_divider_ops = {
>  	.recalc_rate = imx8m_clk_composite_divider_recalc_rate,
>  	.round_rate = imx8m_clk_composite_divider_round_rate,
>  	.set_rate = imx8m_clk_composite_divider_set_rate,
> +	.determine_rate = imx8m_divider_determine_rate,
>  };
>  
>  static u8 imx8m_clk_composite_mux_get_parent(struct clk_hw *hw)
> -- 
> 2.39.2
>