cpufreq: add support for intermediate (stable) frequencies

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index 3f45889..ec4112d 100644
@@ -75,6 +75,7 @@ struct cpufreq_policy {
 	unsigned int		max;    /* in kHz */
 	unsigned int		cur;    /* in kHz, only needed if cpufreq
 					 * governors are used */
+	unsigned int		restore_freq; /* = policy->cur before transition */
 	unsigned int		suspend_freq; /* freq to set during suspend */
 
 	unsigned int		policy; /* see above */

@@ -221,11 +222,35 @@ struct cpufreq_driver {
 
 	/* define one out of two */
 	int	(*setpolicy)	(struct cpufreq_policy *policy);
+
+	/*
+	 * On failure, should always restore frequency to policy->restore_freq
+	 * (i.e. old freq).
+	 */
 	int	(*target)	(struct cpufreq_policy *policy,	/* Deprecated */
 				 unsigned int target_freq,
 				 unsigned int relation);
 	int	(*target_index)	(struct cpufreq_policy *policy,
 				 unsigned int index);
+	/*
+	 * Only for drivers with target_index() and CPUFREQ_ASYNC_NOTIFICATION
+	 * unset.
+	 *
+	 * get_intermediate should return a stable intermediate frequency
+	 * platform wants to switch to and target_intermediate() should set CPU
+	 * to to that frequency, before jumping to the frequency corresponding
+	 * to 'index'. Core will take care of sending notifications and driver
+	 * doesn't have to handle them in target_intermediate() or
+	 * target_index().
+	 *
+	 * Drivers can return '0' from get_intermediate() in case they don't
+	 * wish to switch to intermediate frequency for some target frequency.
+	 * In that case core will directly call ->target_index().
+	 */
+	unsigned int (*get_intermediate)(struct cpufreq_policy *policy,
+					 unsigned int index);
+	int	(*target_intermediate)(struct cpufreq_policy *policy,
+				       unsigned int index);
 
 	/* should be defined, if possible */
 	unsigned int	(*get)	(unsigned int cpu);

index 6e774c6..a5fbc0a 100644
@@ -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 bool pll_x_prepared;
 
-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_x_prepared = true;
 
-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_x_prepared) {
+		clk_disable_unprepare(pll_x_clk);
+		pll_x_prepared = false;
+	}
 
 	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
 };