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

[Stephen Boyd]

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.