linux-kernel - Re: [PATCH 4/4] clk: ti: add am33xx spread spectrum clock support

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Date:   Tue, 16 Mar 2021 13:52:19 +0200
From:   Grygorii Strashko <grygorii.strashko@...com>
To:     Dario Binacchi <dariobin@...ero.it>,
        <linux-kernel@...r.kernel.org>,
        "Vutla, Lokesh" <lokeshvutla@...com>, "Menon, Nishanth" <nm@...com>
CC:     Benoît Cousson <bcousson@...libre.com>,
        Lee Jones <lee.jones@...aro.org>,
        Michael Turquette <mturquette@...libre.com>,
        Rob Herring <robh+dt@...nel.org>,
        Stephen Boyd <sboyd@...nel.org>,
        Tero Kristo <kristo@...nel.org>,
        Tony Lindgren <tony@...mide.com>, <devicetree@...r.kernel.org>,
        <linux-clk@...r.kernel.org>, <linux-omap@...r.kernel.org>
Subject: Re: [PATCH 4/4] clk: ti: add am33xx spread spectrum clock support



On 14/03/2021 17:12, Dario Binacchi wrote:
> The patch enables spread spectrum clocking (SSC) for MPU and LCD PLLs.
> As reported by the TI spruh73x RM, SSC is only supported for the
> DISP/LCD and MPU PLLs on am33xx device. SSC is not supported for DDR,
> PER, and CORE PLLs.
> 
> Calculating the required values and setting the registers accordingly
> was taken from the set_mpu_spreadspectrum routine contained in the
> arch/arm/mach-omap2/am33xx/clock_am33xx.c file of the u-boot project.
> 
> In locked condition, DPLL output clock = CLKINP *[M/N]. In case of
> SSC enabled, the AM335x reference manual explains that there is a
> restriction of range of M values. Since the omap2_dpll_round_rate
> routine attempts to select the minimum possible N, the value of M
> obtained is not guaranteed to be within the range required. With the new
> "ti,min-div" parameter it is possible to increase N and consequently M
> to satisfy the constraint imposed by SSC.
> 
> Signed-off-by: Dario Binacchi <dariobin@...ero.it>
> 
> ---
> 
>   arch/arm/boot/dts/am33xx-clocks.dtsi |  4 +-
>   drivers/clk/ti/dpll.c                | 41 ++++++++++++++
>   drivers/clk/ti/dpll3xxx.c            | 85 ++++++++++++++++++++++++++++
>   include/linux/clk/ti.h               | 24 ++++++++
>   4 files changed, 152 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/arm/boot/dts/am33xx-clocks.dtsi b/arch/arm/boot/dts/am33xx-clocks.dtsi
> index e7bbbf536a8c..a02e0b1229a4 100644
> --- a/arch/arm/boot/dts/am33xx-clocks.dtsi
> +++ b/arch/arm/boot/dts/am33xx-clocks.dtsi
> @@ -164,7 +164,7 @@
>   		#clock-cells = <0>;
>   		compatible = "ti,am3-dpll-core-clock";
>   		clocks = <&sys_clkin_ck>, <&sys_clkin_ck>;
> -		reg = <0x0490>, <0x045c>, <0x0468>, <0x0460>, <0x0464>;
> +		reg = <0x0490>, <0x045c>, <0x0468>;
>   	};
>   
>   	dpll_core_x2_ck: dpll_core_x2_ck {
> @@ -204,7 +204,7 @@
>   		#clock-cells = <0>;
>   		compatible = "ti,am3-dpll-clock";
>   		clocks = <&sys_clkin_ck>, <&sys_clkin_ck>;
> -		reg = <0x0488>, <0x0420>, <0x042c>;
> +		reg = <0x0488>, <0x0420>, <0x042c>, <0x0424>, <0x0428>;
>   	};

You can't mix DT vs code.

>   
>   	dpll_mpu_m2_ck: dpll_mpu_m2_ck@4a8 {
> diff --git a/drivers/clk/ti/dpll.c b/drivers/clk/ti/dpll.c
> index d6f1ac5b53e1..2738417a47b7 100644
> --- a/drivers/clk/ti/dpll.c
> +++ b/drivers/clk/ti/dpll.c
> @@ -290,7 +290,9 @@ static void __init of_ti_dpll_setup(struct device_node *node,
>   	struct clk_init_data *init = NULL;
>   	const char **parent_names = NULL;
>   	struct dpll_data *dd = NULL;
> +	int ssc_clk_index;
>   	u8 dpll_mode = 0;
> +	u32 min_div;
>   
>   	dd = kmemdup(ddt, sizeof(*dd), GFP_KERNEL);
>   	clk_hw = kzalloc(sizeof(*clk_hw), GFP_KERNEL);
> @@ -345,6 +347,27 @@ static void __init of_ti_dpll_setup(struct device_node *node,
>   	if (dd->autoidle_mask) {
>   		if (ti_clk_get_reg_addr(node, 3, &dd->autoidle_reg))
>   			goto cleanup;
> +
> +		ssc_clk_index = 4;
> +	} else {
> +		ssc_clk_index = 3;
> +	}
> +
> +	if (dd->ssc_deltam_int_mask && dd->ssc_deltam_frac_mask &&
> +	    dd->ssc_modfreq_mant_mask && dd->ssc_modfreq_exp_mask) {
> +		if (ti_clk_get_reg_addr(node, ssc_clk_index++,
> +					&dd->ssc_deltam_reg))
> +			goto cleanup;
> +
> +		if (ti_clk_get_reg_addr(node, ssc_clk_index++,
> +					&dd->ssc_modfreq_reg))
> +			goto cleanup;
> +
> +		of_property_read_u32(node, "ti,ssc-modfreq", &dd->ssc_modfreq);
> +		of_property_read_u32(node, "ti,ssc-deltam", &dd->ssc_deltam);
> +		if (of_property_read_bool(node, "ti,ssc-downspread"))
> +			dd->ssc_downspread = 1;

New bindings.

> +
>   	}
>   
>   	if (of_property_read_bool(node, "ti,low-power-stop"))
> @@ -356,6 +379,10 @@ static void __init of_ti_dpll_setup(struct device_node *node,
>   	if (of_property_read_bool(node, "ti,lock"))
>   		dpll_mode |= 1 << DPLL_LOCKED;
>   
> +	if (!of_property_read_u32(node, "ti,min-div", &min_div) &&
> +	    min_div > dd->min_divider)
> +		dd->min_divider = min_div;
> +

New bindings.

[...]

-- 
Best regards,
grygorii