Messages in this thread Patches in this message | | | Date | Mon, 2 Jun 2014 15:36:37 +0530 | Subject | Re: [PATCH V4 3/3] cpufreq: Tegra: implement intermediate frequency callbacks | From | Viresh Kumar <> |
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On 30 May 2014 21:56, Stephen Warren <swarren@wwwdotorg.org> wrote: > I believe the issue is this: > > We can't change the rate of pll_x while it's being used as a source for > something. I'm not 100% sure why. I assume the PLL output simply isn't > stable enough while changing rates; perhaps it can go out-of-range, or > generate glitches. > > This means we must switch the CPU clock source to something else (we use > pll_p) while changing the pll_x rate. > > Since the CPU is the only thing that uses pll_x, if we switch the CPU to > some other clock source, pll_x will become unused, so it will be > automatically disabled. > > Disabling the PLL, and then re-enabling it later when switching the CPU > back to it, presumably takes some extra time (e.g. waiting for PLL lock > when it starts back up), so the code takes an extra reference to the > clock (prepare_enable) before switching the CPU away from it, and drops > that (disable_unprepare) after switching the CPU back to it. > > The only case pll_x is disabled is when we use a cpufreq of 216MHz; that > frequency is provided by pll_p itself, so we never switch back to pll_x > in this case, and do want to shut down pll_x to save some power. > > Now, in your patch when switching from 216MHz to pll_x, the initial > prepare_enable(pll_x) never happens, then the CPU is switched back to > pll_x which turns it on, then the unpaired disable_unprepare(pll_x) > happens which turns off pll_x even though the CPU is using it as clock > source. Arguably the clock API has a bug in that it shouldn't allow > these unpaired calls to break the reference counting, but that's the way > the API is right now.
Okay, that was very helpful..
What about this ? (Attached for testing) :
Author: Viresh Kumar <viresh.kumar@linaro.org> Date: Fri May 16 14:22:40 2014 +0530
cpufreq: Tegra: implement intermediate frequency callbacks
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.
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org> --- drivers/cpufreq/tegra-cpufreq.c | 97 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++----------------------------------- 1 file changed, 62 insertions(+), 35 deletions(-)
diff --git a/drivers/cpufreq/tegra-cpufreq.c b/drivers/cpufreq/tegra-cpufreq.c index 6e774c6..25c145a 100644 --- a/drivers/cpufreq/tegra-cpufreq.c +++ b/drivers/cpufreq/tegra-cpufreq.c @@ -45,46 +45,51 @@ static struct clk *cpu_clk; static struct clk *pll_x_clk; static struct clk *pll_p_clk; static struct clk *emc_clk; +static int pll_p_clk_count;
-static int tegra_cpu_clk_set_rate(unsigned long rate) +static unsigned int tegra_get_intermediate(struct cpufreq_policy *policy, + unsigned int index) +{ + 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; + + return ifreq; +} + +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 + * off when we move the cpu off of it as enabling it again while we + * switch to it from tegra_target() would take additional time. Though + * when target-freq is intermediate freq, we don't need to take this + * reference. */ clk_prepare_enable(pll_x_clk);
ret = clk_set_parent(cpu_clk, pll_p_clk); - if (ret) { - pr_err("Failed to switch cpu to clock pll_p\n"); - goto out; - } - - if (rate == clk_get_rate(pll_p_clk)) - goto out; - - ret = clk_set_rate(pll_x_clk, rate); - if (ret) { - pr_err("Failed to change pll_x to %lu\n", rate); - goto out; - } - - ret = clk_set_parent(cpu_clk, pll_x_clk); - if (ret) { - pr_err("Failed to switch cpu to clock pll_x\n"); - goto out; - } + if (ret) + clk_disable_unprepare(pll_x_clk); + else + pll_p_clk_count++;
-out: - clk_disable_unprepare(pll_x_clk); return ret; }
static int tegra_target(struct cpufreq_policy *policy, unsigned int index) { unsigned long rate = freq_table[index].frequency; + unsigned int ifreq = clk_get_rate(pll_p_clk) / 1000; int ret = 0;
/* @@ -98,10 +103,30 @@ 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, don't need to take extra reference to pll_x_clk + * as it isn't used anymore. + */ + if (rate == ifreq) + return clk_set_parent(cpu_clk, pll_p_clk); + + 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); + + /* + * Drop count to pll_x clock only if we switched to intermediate freq + * earlier while transitioning to a target frequency. + */ + if (pll_p_clk_count) { + clk_disable_unprepare(pll_x_clk); + pll_p_clk_count--; + }
return ret; } @@ -137,16 +162,18 @@ static int tegra_cpu_exit(struct cpufreq_policy *policy) }
static struct cpufreq_driver tegra_cpufreq_driver = { - .flags = CPUFREQ_NEED_INITIAL_FREQ_CHECK, - .verify = cpufreq_generic_frequency_table_verify, - .target_index = tegra_target, - .get = cpufreq_generic_get, - .init = tegra_cpu_init, - .exit = tegra_cpu_exit, - .name = "tegra", - .attr = cpufreq_generic_attr, + .flags = CPUFREQ_NEED_INITIAL_FREQ_CHECK, + .verify = cpufreq_generic_frequency_table_verify, + .get_intermediate = tegra_get_intermediate, + .target_intermediate = tegra_target_intermediate, + .target_index = tegra_target, + .get = cpufreq_generic_get, + .init = tegra_cpu_init, + .exit = tegra_cpu_exit, + .name = "tegra", + .attr = cpufreq_generic_attr, #ifdef CONFIG_PM - .suspend = cpufreq_generic_suspend, + .suspend = cpufreq_generic_suspend, #endif }; From fb2d82a52d95bbd20e4eb75b3b79f74efa4c1a75 Mon Sep 17 00:00:00 2001 Message-Id: <fb2d82a52d95bbd20e4eb75b3b79f74efa4c1a75.1401703573.git.viresh.kumar@linaro.org> From: Viresh Kumar <viresh.kumar@linaro.org> Date: Fri, 16 May 2014 14:22:40 +0530 Subject: [PATCH] cpufreq: Tegra: implement intermediate frequency callbacks
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.
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org> --- drivers/cpufreq/tegra-cpufreq.c | 97 ++++++++++++++++++++++++++--------------- 1 file changed, 62 insertions(+), 35 deletions(-)
diff --git a/drivers/cpufreq/tegra-cpufreq.c b/drivers/cpufreq/tegra-cpufreq.c index 6e774c6..25c145a 100644 --- a/drivers/cpufreq/tegra-cpufreq.c +++ b/drivers/cpufreq/tegra-cpufreq.c @@ -45,46 +45,51 @@ static struct clk *cpu_clk; static struct clk *pll_x_clk; static struct clk *pll_p_clk; static struct clk *emc_clk; +static int pll_p_clk_count; -static int tegra_cpu_clk_set_rate(unsigned long rate) +static unsigned int tegra_get_intermediate(struct cpufreq_policy *policy, + unsigned int index) +{ + 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; + + return ifreq; +} + +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 + * off when we move the cpu off of it as enabling it again while we + * switch to it from tegra_target() would take additional time. Though + * when target-freq is intermediate freq, we don't need to take this + * reference. */ clk_prepare_enable(pll_x_clk); ret = clk_set_parent(cpu_clk, pll_p_clk); - if (ret) { - pr_err("Failed to switch cpu to clock pll_p\n"); - goto out; - } - - if (rate == clk_get_rate(pll_p_clk)) - goto out; - - ret = clk_set_rate(pll_x_clk, rate); - if (ret) { - pr_err("Failed to change pll_x to %lu\n", rate); - goto out; - } - - ret = clk_set_parent(cpu_clk, pll_x_clk); - if (ret) { - pr_err("Failed to switch cpu to clock pll_x\n"); - goto out; - } + if (ret) + clk_disable_unprepare(pll_x_clk); + else + pll_p_clk_count++; -out: - clk_disable_unprepare(pll_x_clk); return ret; } static int tegra_target(struct cpufreq_policy *policy, unsigned int index) { unsigned long rate = freq_table[index].frequency; + unsigned int ifreq = clk_get_rate(pll_p_clk) / 1000; int ret = 0; /* @@ -98,10 +103,30 @@ 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, don't need to take extra reference to pll_x_clk + * as it isn't used anymore. + */ + if (rate == ifreq) + return clk_set_parent(cpu_clk, pll_p_clk); + + 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); + + /* + * Drop count to pll_x clock only if we switched to intermediate freq + * earlier while transitioning to a target frequency. + */ + if (pll_p_clk_count) { + clk_disable_unprepare(pll_x_clk); + pll_p_clk_count--; + } return ret; } @@ -137,16 +162,18 @@ static int tegra_cpu_exit(struct cpufreq_policy *policy) } static struct cpufreq_driver tegra_cpufreq_driver = { - .flags = CPUFREQ_NEED_INITIAL_FREQ_CHECK, - .verify = cpufreq_generic_frequency_table_verify, - .target_index = tegra_target, - .get = cpufreq_generic_get, - .init = tegra_cpu_init, - .exit = tegra_cpu_exit, - .name = "tegra", - .attr = cpufreq_generic_attr, + .flags = CPUFREQ_NEED_INITIAL_FREQ_CHECK, + .verify = cpufreq_generic_frequency_table_verify, + .get_intermediate = tegra_get_intermediate, + .target_intermediate = tegra_target_intermediate, + .target_index = tegra_target, + .get = cpufreq_generic_get, + .init = tegra_cpu_init, + .exit = tegra_cpu_exit, + .name = "tegra", + .attr = cpufreq_generic_attr, #ifdef CONFIG_PM - .suspend = cpufreq_generic_suspend, + .suspend = cpufreq_generic_suspend, #endif }; -- 2.0.0.rc2
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