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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <DB3PR0402MB3916BA142113B84C0199C93EF5780@DB3PR0402MB3916.eurprd04.prod.outlook.com>
Date:   Sat, 23 Feb 2019 02:32:28 +0000
From:   Anson Huang <anson.huang@....com>
To:     Stephen Boyd <sboyd@...nel.org>,
        "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>,
        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

Hi, Stehpen

Best Regards!
Anson Huang

> -----Original Message-----
> From: Stephen Boyd [mailto:sboyd@...nel.org]
> Sent: 2019年2月23日 3:08
> To: devicetree@...r.kernel.org; festevam@...il.com;
> kernel@...gutronix.de; linux-arm-kernel@...ts.infradead.org; linux-
> clk@...r.kernel.org; linux-kernel@...r.kernel.org; mark.rutland@....com;
> mturquette@...libre.com; robh+dt@...nel.org; s.hauer@...gutronix.de;
> 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?

The i.MX8QXP ONLY has 1 cluster named A35, while on i.MX8QM there will be
2 clusters, A53 and A72, so we need to use the resource ID to initialize the cluster_id.

> 
> > +
> > +       /* 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.

 89 +       if (rsrc_id == IMX_SC_R_A35)
 90 +               init.ops = &clk_scu_cpu_ops;
 91 +       else
 92 +               init.ops = &clk_scu_ops;

I think it should be good. Only when plan to support cpu-freq scaling, then the
CPU clock will be switched to use clk_scu_cpu_ops and the clutser_id initialization
will be done according to CPU resource. For example, when we plan to support i.MX8QM
cpu-freq scaling, we will add A53 and A72 check here and switch the clock ops to clk_scu_cpu_ops,
also we will add the cluster_id initialization in the SMC clock set rate.

Thanks,
Anson.

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