soc/tegra: pmc: Ensure that clock rates aren't too high

Switch all clocks of a power domain to a safe rate which is suitable
for all possible voltages in order to ensure that hardware constraints
aren't violated when power domain state toggles.

Tested-by: Peter Geis <pgwipeout@gmail.com> # Ouya T30
Tested-by: Nicolas Chauvet <kwizart@gmail.com> # PAZ00 T20 and TK1 T124
Tested-by: Matt Merhar <mattmerhar@protonmail.com> # Ouya T30
Signed-off-by: NDmitry Osipenko <digetx@gmail.com>
Signed-off-by: NThierry Reding <treding@nvidia.com>

drivers/soc/tegra/pmc.c

@@ -258,6 +258,7 @@ struct tegra_powergate {
 	unsigned int id;
 	struct clk **clks;
 	unsigned int num_clks;
+	unsigned long *clk_rates;
 	struct reset_control *reset;
 };
 
@@ -663,6 +664,57 @@ static int __tegra_powergate_remove_clamping(struct tegra_pmc *pmc,
 	return 0;
 }
 
+static int tegra_powergate_prepare_clocks(struct tegra_powergate *pg)
+{
+	unsigned long safe_rate = 100 * 1000 * 1000;
+	unsigned int i;
+	int err;
+
+	for (i = 0; i < pg->num_clks; i++) {
+		pg->clk_rates[i] = clk_get_rate(pg->clks[i]);
+
+		if (!pg->clk_rates[i]) {
+			err = -EINVAL;
+			goto out;
+		}
+
+		if (pg->clk_rates[i] <= safe_rate)
+			continue;
+
+		/*
+		 * We don't know whether voltage state is okay for the
+		 * current clock rate, hence it's better to temporally
+		 * switch clock to a safe rate which is suitable for
+		 * all voltages, before enabling the clock.
+		 */
+		err = clk_set_rate(pg->clks[i], safe_rate);
+		if (err)
+			goto out;
+	}
+
+	return 0;
+
+out:
+	while (i--)
+		clk_set_rate(pg->clks[i], pg->clk_rates[i]);
+
+	return err;
+}
+
+static int tegra_powergate_unprepare_clocks(struct tegra_powergate *pg)
+{
+	unsigned int i;
+	int err;
+
+	for (i = 0; i < pg->num_clks; i++) {
+		err = clk_set_rate(pg->clks[i], pg->clk_rates[i]);
+		if (err)
+			return err;
+	}
+
+	return 0;
+}
+
 static void tegra_powergate_disable_clocks(struct tegra_powergate *pg)
 {
 	unsigned int i;
@@ -713,10 +765,14 @@ static int tegra_powergate_power_up(struct tegra_powergate *pg,
 
 	usleep_range(10, 20);
 
-	err = tegra_powergate_enable_clocks(pg);
+	err = tegra_powergate_prepare_clocks(pg);
 	if (err)
 		goto powergate_off;
 
+	err = tegra_powergate_enable_clocks(pg);
+	if (err)
+		goto unprepare_clks;
+
 	usleep_range(10, 20);
 
 	err = __tegra_powergate_remove_clamping(pg->pmc, pg->id);
@@ -739,12 +795,19 @@ static int tegra_powergate_power_up(struct tegra_powergate *pg,
 	if (disable_clocks)
 		tegra_powergate_disable_clocks(pg);
 
+	err = tegra_powergate_unprepare_clocks(pg);
+	if (err)
+		return err;
+
 	return 0;
 
 disable_clks:
 	tegra_powergate_disable_clocks(pg);
 	usleep_range(10, 20);
 
+unprepare_clks:
+	tegra_powergate_unprepare_clocks(pg);
+
 powergate_off:
 	tegra_powergate_set(pg->pmc, pg->id, false);
 
@@ -755,10 +818,14 @@ static int tegra_powergate_power_down(struct tegra_powergate *pg)
 {
 	int err;
 
-	err = tegra_powergate_enable_clocks(pg);
+	err = tegra_powergate_prepare_clocks(pg);
 	if (err)
 		return err;
 
+	err = tegra_powergate_enable_clocks(pg);
+	if (err)
+		goto unprepare_clks;
+
 	usleep_range(10, 20);
 
 	err = reset_control_assert(pg->reset);
@@ -775,6 +842,10 @@ static int tegra_powergate_power_down(struct tegra_powergate *pg)
 	if (err)
 		goto assert_resets;
 
+	err = tegra_powergate_unprepare_clocks(pg);
+	if (err)
+		return err;
+
 	return 0;
 
 assert_resets:
@@ -786,6 +857,9 @@ static int tegra_powergate_power_down(struct tegra_powergate *pg)
 disable_clks:
 	tegra_powergate_disable_clocks(pg);
 
+unprepare_clks:
+	tegra_powergate_unprepare_clocks(pg);
+
 	return err;
 }
 
@@ -903,6 +977,12 @@ int tegra_powergate_sequence_power_up(unsigned int id, struct clk *clk,
 	if (!pg)
 		return -ENOMEM;
 
+	pg->clk_rates = kzalloc(sizeof(*pg->clk_rates), GFP_KERNEL);
+	if (!pg->clk_rates) {
+		kfree(pg->clks);
+		return -ENOMEM;
+	}
+
 	pg->id = id;
 	pg->clks = &clk;
 	pg->num_clks = 1;
@@ -914,6 +994,7 @@ int tegra_powergate_sequence_power_up(unsigned int id, struct clk *clk,
 		dev_err(pmc->dev, "failed to turn on partition %d: %d\n", id,
 			err);
 
+	kfree(pg->clk_rates);
 	kfree(pg);
 
 	return err;
@@ -1064,6 +1145,12 @@ static int tegra_powergate_of_get_clks(struct tegra_powergate *pg,
 	if (!pg->clks)
 		return -ENOMEM;
 
+	pg->clk_rates = kcalloc(count, sizeof(*pg->clk_rates), GFP_KERNEL);
+	if (!pg->clk_rates) {
+		kfree(pg->clks);
+		return -ENOMEM;
+	}
+
 	for (i = 0; i < count; i++) {
 		pg->clks[i] = of_clk_get(np, i);
 		if (IS_ERR(pg->clks[i])) {
@@ -1080,6 +1167,7 @@ static int tegra_powergate_of_get_clks(struct tegra_powergate *pg,
 	while (i--)
 		clk_put(pg->clks[i]);
 
+	kfree(pg->clk_rates);
 	kfree(pg->clks);
 
 	return err;