Messages in this thread | | | Date | Thu, 29 May 2014 11:40:19 -0600 | From | Stephen Warren <> | Subject | Re: [PATCH V4 3/3] cpufreq: Tegra: implement intermediate frequency callbacks |
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On 05/21/2014 02:59 AM, Viresh Kumar wrote: > Tegra had always been switching to intermediate frequency (pll_p_clk) since > ever. CPUFreq core has better support for handling notifications for these > frequencies and so we can adapt Tegra's driver to it. > > Also do a WARN() if clk_set_parent() fails while moving back to pll_x as we > should have atleast restored to earlier frequency on error.
This patch breaks Tegra. The reason is below.
> diff --git a/drivers/cpufreq/tegra-cpufreq.c b/drivers/cpufreq/tegra-cpufreq.c
> -static int tegra_cpu_clk_set_rate(unsigned long rate) > +static unsigned int > +tegra_get_intermediate(struct cpufreq_policy *policy, unsigned int index)
(BTW, can we please not put the return type on a separate line; it's inconsistent with the rest of the code in this file)
> +{ > + unsigned int ifreq = clk_get_rate(pll_p_clk) / 1000; > + > + /* > + * Don't switch to intermediate freq if: > + * - we are already at it, i.e. policy->cur == ifreq > + * - index corresponds to ifreq > + */ > + if ((freq_table[index].frequency == ifreq) || (policy->cur == ifreq)) > + return 0;
If policy->cur == ifreq here, then tegra_target_intermediate() isn't called by the cpufreq core, so ...
> +static int > +tegra_target_intermediate(struct cpufreq_policy *policy, unsigned int index) > { > int ret; > > /* > * Take an extra reference to the main pll so it doesn't turn > * off when we move the cpu off of it > */ > clk_prepare_enable(pll_x_clk);
... that reference isn't added...
> @@ -98,10 +96,23 @@ static int tegra_target(struct cpufreq_policy *policy, unsigned int index) > else > clk_set_rate(emc_clk, 100000000); /* emc 50Mhz */ > > - ret = tegra_cpu_clk_set_rate(rate * 1000); > + /* target freq == pll_p */ > + if (rate * 1000 == clk_get_rate(pll_p_clk)) { > + ret = tegra_target_intermediate(policy, index); > + goto disable_pll_x; > + }
... and this code doesn't call it either, since we could be switching from the pll_p rate to something faster ...
> + > + ret = clk_set_rate(pll_x_clk, rate * 1000); > + /* Restore to earlier frequency on error, i.e. pll_x */ > if (ret) > - pr_err("cpu-tegra: Failed to set cpu frequency to %lu kHz\n", > - rate); > + pr_err("Failed to change pll_x to %lu\n", rate); > + > + ret = clk_set_parent(cpu_clk, pll_x_clk); > + /* This shouldn't fail while changing or restoring */ > + WARN_ON(ret); > + > +disable_pll_x: > + clk_disable_unprepare(pll_x_clk);
... so this turns off pll_x even though we're running from it.
It would be simpler if Tegra *always* used an intermediate frequency, and hence the core *always* called tegra_target_intermediate(). Admittedly, this would result in tegra_target() sometimes (when switching CPU clock rate to the pll_p rate) doing nothing other than removing the extra reference on pll_x, but I think that the code would be simpler to follow and more robust.
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