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

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Message-ID: <DB3PR0402MB3916536B5BDD5CD17E9E04BFF57B0@DB3PR0402MB3916.eurprd04.prod.outlook.com>
Date:   Tue, 26 Feb 2019 05:18:08 +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, Stephen

Best Regards!
Anson Huang

> -----Original Message-----
> From: Stephen Boyd [mailto:sboyd@...nel.org]
> Sent: 2019年2月26日 1:22
> 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 (2019-02-22 18:32:28)
> > > > +               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.
> >
> 
> Ok. So then please make the set_rate function fail if the rsrc_id doesn't
> match something expected. As the code is written right now, the compiler
> can't figure out that cluster_id will always be assigned, so it complains that it
> may be using uninitialized data.

Agreed, I have sent V7 patch series to add return fail if the resource ID is NOT expected.

Thanks,
Anson.