linux-kernel - Re: [PATCH 1/7] PM / OPP: Add platform specific set

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Date:   Wed, 20 Sep 2017 13:30:33 -0700
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     Dong Aisheng <dongas86@...il.com>
Cc:     Dong Aisheng <aisheng.dong@....com>, linux-pm@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        sboyd@...eaurora.org, vireshk@...nel.org, nm@...com,
        rjw@...ysocki.net, shawnguo@...nel.org, Anson.Huang@....com,
        ping.bai@....com
Subject: Re: [PATCH 1/7] PM / OPP: Add platform specific set_clk function

On 20-09-17, 15:03, Dong Aisheng wrote:
> I've been thinking of that before.
> Actually IMX already does some similar thing for MX5 (no for MX6).
> See: clk_cpu_set_rate() in drivers/clk/imx/clk-cpu.c.
> 
> After some diggings, it seems MX7ULP is a bit more complicated than before
> mainly due to two reasons:
> 1) It requires to switch to different CPU mode accordingly when setting
> clocks rate. That means we need handle this in clock driver as well
> which looks not quite suitable although we could do if really want.
> 
> 2) It uses different clocks for different CPU mode (RUN 416M or
> HSRUN 528M), and those clocks have some dependency.
> e.g. when setting HSRUN clock, we need change RUN clock parent to make sure
> the SPLL_PFD is got disabled before changing rate, as both CPU mode using
> the same parent SPLL_PFD clock. Doing this in clock driver also make things
> a bit more complicated.
> 
> The whole follow would be something like below:
> static int imx7ulp_set_clk(struct device *dev, struct clk *clk,
>                            unsigned long old_freq, unsigned long new_freq)
> {
>         u32 val;
> 
>         /*
>          * Before changing the ARM core PLL, change the ARM clock soure
>          * to FIRC first.
>          */
>         if (new_freq >= HSRUN_FREQ) {
>                 clk_set_parent(clks[RUN_SCS_SEL].clk, clks[FIRC].clk);
> 
>                 /* switch to HSRUN mode */
>                 val = readl_relaxed(smc_base + SMC_PMCTRL);
>                 val |= (0x3 << 8);
>                 writel_relaxed(val, smc_base + SMC_PMCTRL);
> 
>                 /* change the clock rate in HSRUN */
>                 clk_set_rate(clks[SPLL_PFD0].clk, new_freq);
>                 clk_set_parent(clks[HSRUN_SCS_SEL].clk, clks[SPLL_SEL].clk);
>         } else {
>                 /* change the HSRUN clock to firc */
>                 clk_set_parent(clks[HSRUN_SCS_SEL].clk, clks[FIRC].clk);
> 
>                 /* switch to RUN mode */
>                 val = readl_relaxed(smc_base + SMC_PMCTRL);
>                 val &= ~(0x3 << 8);
>                 writel_relaxed(val, smc_base + SMC_PMCTRL);
> 
>                 clk_set_rate(clks[SPLL_PFD0].clk, new_freq);
>                 clk_set_parent(clks[RUN_SCS_SEL].clk, clks[SPLL_SEL].clk);
>         }
> 
>         return 0;
> }

Right and we have the same thing in the cpufreq driver now. It will
stay at some place and we need to find the best one, keeping in mind
that we may or may not want to solve this problem in a generic way.

> That's why i thought if we can make OPP core provide a way to handle such
> complicated things in platform specific cpufreq driver.
> 
> How would you suggest for this issue?

I wouldn't add an API into the OPP framework if I were you. There is
just too much code to add to the core to handle such platform specific
stuff, which you are anyway going to keep somewhere as it is. IMHO,
keeping that in the clock driver is a better thing to do than this.

-- 
viresh