linux-kernel - RE: [PATCH] clk: imx: composite-8m: Fix clock divisions greater than 8

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Date:   Mon, 17 Apr 2023 00:55:06 +0000
From:   Peng Fan <peng.fan@....com>
To:     Adam Ford <aford173@...il.com>,
        "linux-clk@...r.kernel.org" <linux-clk@...r.kernel.org>
CC:     "aford@...conembedded.com" <aford@...conembedded.com>,
        Abel Vesa <abelvesa@...nel.org>,
        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>,
        dl-linux-imx <linux-imx@....com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH] clk: imx: composite-8m:  Fix clock divisions greater than
 8

> Subject: [PATCH] clk: imx: composite-8m: Fix clock divisions greater than 8
> 
> When adding imx8m_clk_divider_determine_rate to let the imx8mm and
> imx8mn get finer granulatiry of video clocks, it accidentally broke the
> imx8mp ability to divide clocks by more than 8 on clocks when the
> CLK_SET_RATE_PARENT flag is not set.
> 
> On the imx8mp, the CLK_SET_RATE_PARENT flag cannot be set on either
> media_disp1_pix or media_disp2_pix, because they both share the
> video_pll as a common clock, and if two displays are used, the parent clock
> needs to be something that both child clocks can divide.
> 
> imx8m_clk_divider_determine_rate ends up calling clk_divider_bestdiv
> which uses the value of 'width' to setup the maximum divisor.  The clk-
> composite-8m driver sets the with to 3 which means the maximum divisor is
> 8, but these clocks can divide by up to 64.
> 
> Currently, if the video_pll is set to 1039500000, the slowest clock rate
> achievable is 129937500 which breaks a whole bunch of lower resolution
> and refresh options for both media_disp1_pix and media_disp2_pix.
> 
> By changing the 'width' variable to PCG_DIV_WIDTH, the maximum divisor
> becomes 64 which allows the clocks to divide down more, so the lower
> resolutions and refresh rates are achievable again.
> 
> Fixes: 156e96ff2172 ("clk: imx: composite-8m: Add support to
> determine_rate")
> Signed-off-by: Adam Ford <aford173@...il.com>
> 
> diff --git a/drivers/clk/imx/clk-composite-8m.c b/drivers/clk/imx/clk-
> composite-8m.c
> index 6883a8199b6c..805e6aada83d 100644
> --- a/drivers/clk/imx/clk-composite-8m.c
> +++ b/drivers/clk/imx/clk-composite-8m.c
> @@ -47,6 +47,7 @@ static unsigned long
> imx8m_clk_composite_divider_recalc_rate(struct clk_hw *hw,
>  				   divider->flags, PCG_DIV_WIDTH);
>  }
> 
> +
>  static int imx8m_clk_composite_compute_dividers(unsigned long rate,
>  						unsigned long parent_rate,
>  						int *prediv, int *postdiv)
> @@ -215,12 +216,12 @@ struct clk_hw *__imx8m_clk_hw_composite(const
> char *name,
>  		mux_ops = &imx8m_clk_composite_mux_ops;
>  	} else if (composite_flags & IMX_COMPOSITE_BUS) {
>  		div->shift = PCG_PREDIV_SHIFT;
> -		div->width = PCG_PREDIV_WIDTH;
> +		div->width = PCG_DIV_WIDTH;
This is wrong. Pre divider width is 3, not 6.

>  		divider_ops = &imx8m_clk_composite_divider_ops;
>  		mux_ops = &imx8m_clk_composite_mux_ops;
>  	} else {
>  		div->shift = PCG_PREDIV_SHIFT;
> -		div->width = PCG_PREDIV_WIDTH;
> +		div->width = PCG_DIV_WIDTH;
Ditto.

You need find the other way to resolve the regression.

Regards,
Peng.

>  		divider_ops = &imx8m_clk_composite_divider_ops;
>  		mux_ops = &clk_mux_ops;
>  		if (!(composite_flags & IMX_COMPOSITE_FW_MANAGED))
> --
> 2.39.2