soc/tegra: pmc: Query PCLK clock rate at probe time

It is possible to get a lockup if kernel decides to enter LP2 cpuidle
from some clk-notifier, in that case CCF's "prepare" mutex is kept locked
and thus clk_get_rate(pclk) blocks on the same mutex with interrupts being
disabled, hanging machine.
Signed-off-by: Dmitry Osipenko <digetx@gmail.com>
Acked-By: Peter De Schrijver <pdeschrijver@nvidia.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>

drivers/soc/tegra/pmc.c

@@ -324,6 +324,7 @@ static const char * const tegra210_reset_sources[] = {
  * @pctl_dev: pin controller exposed by the PMC
  * @domain: IRQ domain provided by the PMC
  * @irq: chip implementation for the IRQ domain
+ * @clk_nb: pclk clock changes handler
  */
 struct tegra_pmc {
 	struct device *dev;
@@ -359,6 +360,8 @@ struct tegra_pmc {
 
 	struct irq_domain *domain;
 	struct irq_chip irq;
+
+	struct notifier_block clk_nb;
 };
 
 static struct tegra_pmc *pmc = &(struct tegra_pmc) {
@@ -1207,7 +1210,7 @@ static int tegra_io_pad_prepare(struct tegra_pmc *pmc, enum tegra_io_pad id,
 		return err;
 
 	if (pmc->clk) {
-		rate = clk_get_rate(pmc->clk);
+		rate = pmc->rate;
 		if (!rate) {
 			dev_err(pmc->dev, "failed to get clock rate\n");
 			return -ENODEV;
@@ -1448,6 +1451,7 @@ void tegra_pmc_set_suspend_mode(enum tegra_suspend_mode mode)
 void tegra_pmc_enter_suspend_mode(enum tegra_suspend_mode mode)
 {
 	unsigned long long rate = 0;
+	u64 ticks;
 	u32 value;
 
 	switch (mode) {
@@ -1456,7 +1460,7 @@ void tegra_pmc_enter_suspend_mode(enum tegra_suspend_mode mode)
 		break;
 
 	case TEGRA_SUSPEND_LP2:
-		rate = clk_get_rate(pmc->clk);
+		rate = pmc->rate;
 		break;
 
 	default:
@@ -1466,21 +1470,15 @@ void tegra_pmc_enter_suspend_mode(enum tegra_suspend_mode mode)
 	if (WARN_ON_ONCE(rate == 0))
 		rate = 100000000;
 
-	if (rate != pmc->rate) {
-		u64 ticks;
-
-		ticks = pmc->cpu_good_time * rate + USEC_PER_SEC - 1;
-		do_div(ticks, USEC_PER_SEC);
-		tegra_pmc_writel(pmc, ticks, PMC_CPUPWRGOOD_TIMER);
+	ticks = pmc->cpu_good_time * rate + USEC_PER_SEC - 1;
+	do_div(ticks, USEC_PER_SEC);
+	tegra_pmc_writel(pmc, ticks, PMC_CPUPWRGOOD_TIMER);
 
-		ticks = pmc->cpu_off_time * rate + USEC_PER_SEC - 1;
-		do_div(ticks, USEC_PER_SEC);
-		tegra_pmc_writel(pmc, ticks, PMC_CPUPWROFF_TIMER);
+	ticks = pmc->cpu_off_time * rate + USEC_PER_SEC - 1;
+	do_div(ticks, USEC_PER_SEC);
+	tegra_pmc_writel(pmc, ticks, PMC_CPUPWROFF_TIMER);
 
-		wmb();
-
-		pmc->rate = rate;
-	}
+	wmb();
 
 	value = tegra_pmc_readl(pmc, PMC_CNTRL);
 	value &= ~PMC_CNTRL_SIDE_EFFECT_LP0;
@@ -2140,6 +2138,33 @@ static int tegra_pmc_irq_init(struct tegra_pmc *pmc)
 	return 0;
 }
 
+static int tegra_pmc_clk_notify_cb(struct notifier_block *nb,
+				   unsigned long action, void *ptr)
+{
+	struct tegra_pmc *pmc = container_of(nb, struct tegra_pmc, clk_nb);
+	struct clk_notifier_data *data = ptr;
+
+	switch (action) {
+	case PRE_RATE_CHANGE:
+		mutex_lock(&pmc->powergates_lock);
+		break;
+
+	case POST_RATE_CHANGE:
+		pmc->rate = data->new_rate;
+		/* fall through */
+
+	case ABORT_RATE_CHANGE:
+		mutex_unlock(&pmc->powergates_lock);
+		break;
+
+	default:
+		WARN_ON_ONCE(1);
+		return notifier_from_errno(-EINVAL);
+	}
+
+	return NOTIFY_OK;
+}
+
 static int tegra_pmc_probe(struct platform_device *pdev)
 {
 	void __iomem *base;
@@ -2203,6 +2228,23 @@ static int tegra_pmc_probe(struct platform_device *pdev)
 		pmc->clk = NULL;
 	}
 
+	/*
+	 * PCLK clock rate can't be retrieved using CLK API because it
+	 * causes lockup if CPU enters LP2 idle state from some other
+	 * CLK notifier, hence we're caching the rate's value locally.
+	 */
+	if (pmc->clk) {
+		pmc->clk_nb.notifier_call = tegra_pmc_clk_notify_cb;
+		err = clk_notifier_register(pmc->clk, &pmc->clk_nb);
+		if (err) {
+			dev_err(&pdev->dev,
+				"failed to register clk notifier\n");
+			return err;
+		}
+
+		pmc->rate = clk_get_rate(pmc->clk);
+	}
+
 	pmc->dev = &pdev->dev;
 
 	tegra_pmc_init(pmc);
@@ -2254,6 +2296,8 @@ static int tegra_pmc_probe(struct platform_device *pdev)
 cleanup_sysfs:
 	device_remove_file(&pdev->dev, &dev_attr_reset_reason);
 	device_remove_file(&pdev->dev, &dev_attr_reset_level);
+	clk_notifier_unregister(pmc->clk, &pmc->clk_nb);
+
 	return err;
 }