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

[Anson Huang]

Hi, Stehpen

Best Regards!
Anson Huang

> -----Original Message-----
> From: Stephen Boyd [mailto:sboyd@xxxxxxxxxx]
> Sent: 2019å2æ23æ 3:08
> 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 (2019-02-21 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@xxxxxxx>
> 
> 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;
> > +}
> > +