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

[Anson Huang]

Hi, Stephen

Best Regards!
Anson Huang

> -----Original Message-----
> From: Stephen Boyd [mailto:sboyd@xxxxxxxxxx]
> Sent: 2019å2æ26æ 1:22
> To: devicetree@xxxxxxxxxxxxxxx; festevam@xxxxxxxxx;
> kernel@xxxxxxxxxxxxxx; linux-arm-kernel@xxxxxxxxxxxxxxxxxxx; linux-
> clk@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; mark.rutland@xxxxxxx;
> mturquette@xxxxxxxxxxxx; robh+dt@xxxxxxxxxx; s.hauer@xxxxxxxxxxxxxx;
> shawnguo@xxxxxxxxxx; Aisheng Dong <aisheng.dong@xxxxxxx>; Anson
> Huang <anson.huang@xxxxxxx>; Daniel Baluta <daniel.baluta@xxxxxxx>
> Cc: dl-linux-imx <linux-imx@xxxxxxx>
> 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.