linux-kernel - Re: [PATCH RESEND V6 2/2] clk: imx: scu: add cpu frequency scaling support

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Date:   Fri, 22 Feb 2019 11:08:10 -0800
From:   Stephen Boyd <sboyd@...nel.org>
To:     "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "festevam@...il.com" <festevam@...il.com>,
        "kernel@...gutronix.de" <kernel@...gutronix.de>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-clk@...r.kernel.org" <linux-clk@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "mark.rutland@....com" <mark.rutland@....com>,
        "mturquette@...libre.com" <mturquette@...libre.com>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "s.hauer@...gutronix.de" <s.hauer@...gutronix.de>,
        "shawnguo@...nel.org" <shawnguo@...nel.org>,
        Aisheng Dong <aisheng.dong@....com>,
        Anson Huang <anson.huang@....com>,
        Daniel Baluta <daniel.baluta@....com>
Cc:     dl-linux-imx <linux-imx@....com>
Subject: Re: [PATCH RESEND V6 2/2] clk: imx: scu: add cpu frequency scaling support

Quoting Anson Huang (2019-02-21 18:32:10)
> On NXP's i.MX SoCs with system controller inside, CPU frequency
> scaling can ONLY be done by system controller firmware, and it
> can ONLY be requested from secure mode, so Linux kernel has to
> call ARM SMC to trap to ARM-Trusted-Firmware to request system
> controller firmware to do CPU frequency scaling.
> 
> This patch adds i.MX system controller CPU frequency scaling support,
> it reuses cpufreq-dt driver and implement the CPU frequency scaling
> inside SCU clock driver.
> 
> Signed-off-by: Anson Huang <Anson.Huang@....com>

Ah I missed one thing, see below.

> @@ -180,6 +185,23 @@ static long clk_scu_round_rate(struct clk_hw *hw, unsigned long rate,
>         return rate;
>  }
>  
> +static int clk_scu_atf_set_cpu_rate(struct clk_hw *hw, unsigned long rate,
> +                                   unsigned long parent_rate)
> +{
> +       struct clk_scu *clk = to_clk_scu(hw);
> +       struct arm_smccc_res res;
> +       unsigned long cluster_id;
> +
> +       if (clk->rsrc_id == IMX_SC_R_A35)
> +               cluster_id = 0;

Do we still need to check this anymore? Why not just always use
cluster_id 0?

> +
> +       /* CPU frequency scaling can ONLY be done by ARM-Trusted-Firmware */
> +       arm_smccc_smc(IMX_SIP_CPUFREQ, IMX_SIP_SET_CPUFREQ,
> +                     cluster_id, rate, 0, 0, 0, 0, &res);

Because not checking would make this work, vs. checking causes this code
to sometimes use an uninitialized value from the stack.

> +
> +       return 0;
> +}
> +