clk: tegra: Support runtime PM and power domain

The Clock-and-Reset controller resides in a core power domain on NVIDIA
Tegra SoCs.  In order to support voltage scaling of the core power domain,
we hook up DVFS-capable clocks to the core GENPD for managing of the
GENPD's performance state based on the clock changes.

Some clocks don't have any specific physical hardware unit that backs
them, like root PLLs and system clock and they have theirs own voltage
requirements.  This patch adds new clk-device driver that backs the clocks
and provides runtime PM functionality for them.  A virtual clk-device is
created for each such DVFS-capable clock at the clock's registration time
by the new tegra_clk_register() helper.  Driver changes clock's device
GENPD performance state based on clk-rate notifications.

In result we have this sequence of events:

  1. Clock driver creates virtual device for selective clocks, enables
     runtime PM for the created device and registers the clock.
  2. Clk-device driver starts to listen to clock rate changes.
  3. Something changes clk rate or enables/disables clk.
  4. CCF core propagates the change through the clk tree.
  5. Clk-device driver gets clock rate-change notification or GENPD core
     handles prepare/unprepare of the clock.
  6. Clk-device driver changes GENPD performance state on clock rate
     change.
  7. GENPD driver changes voltage regulator state change.
  8. The regulator state is committed to hardware via I2C.

We rely on fact that DVFS is not needed for Tegra I2C and that Tegra I2C
driver already keeps clock always-prepared.  Hence I2C subsystem stays
independent from the clk power management and there are no deadlock spots
in the sequence.

Currently all clocks are registered very early during kernel boot when the
device driver core isn't available yet.  The clk-device can't be created
at that time.  This patch splits the registration of the clocks in two
phases:

  1. Register all essential clocks which don't use RPM and are needed
     during early boot.

  2. Register at a later boot time the rest of clocks.

This patch adds power management support for Tegra20 and Tegra30 clocks.

Reviewed-by: Ulf Hansson <ulf.hansson@linaro.org>
Tested-by: Peter Geis <pgwipeout@gmail.com> # Ouya T30
Tested-by: Paul Fertser <fercerpav@gmail.com> # PAZ00 T20
Tested-by: Nicolas Chauvet <kwizart@gmail.com> # PAZ00 T20 and TK1 T124
Tested-by: Matt Merhar <mattmerhar@protonmail.com> # Ouya T30
Signed-off-by: Dmitry Osipenko <digetx@gmail.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>

1 files changed, 59 insertions, 18 deletions

diff --git a/drivers/clk/tegra/clk-tegra20.c b/drivers/clk/tegra/clk-tegra20.c
index 3664593a5ba4..be3c33441cfc 100644
--- a/drivers/clk/tegra/clk-tegra20.c
+++ b/drivers/clk/tegra/clk-tegra20.c
@@ -6,8 +6,11 @@
 #include <linux/io.h>
 #include <linux/clk-provider.h>
 #include <linux/clkdev.h>
+#include <linux/init.h>
 #include <linux/of.h>
 #include <linux/of_address.h>
+#include <linux/of_device.h>
+#include <linux/platform_device.h>
 #include <linux/clk/tegra.h>
 #include <linux/delay.h>
 #include <dt-bindings/clock/tegra20-car.h>
@@ -414,7 +417,7 @@ static struct tegra_clk_pll_params pll_e_params = {
 	.fixed_rate = 100000000,
 };
 
-static struct tegra_devclk devclks[] __initdata = {
+static struct tegra_devclk devclks[] = {
 	{ .con_id = "pll_c", .dt_id = TEGRA20_CLK_PLL_C },
 	{ .con_id = "pll_c_out1", .dt_id = TEGRA20_CLK_PLL_C_OUT1 },
 	{ .con_id = "pll_p", .dt_id = TEGRA20_CLK_PLL_P },
@@ -710,13 +713,6 @@ static void tegra20_super_clk_init(void)
 			      NULL);
 	clks[TEGRA20_CLK_CCLK] = clk;
 
-	/* SCLK */
-	clk = tegra_clk_register_super_mux("sclk", sclk_parents,
-			      ARRAY_SIZE(sclk_parents),
-			      CLK_SET_RATE_PARENT | CLK_IS_CRITICAL,
-			      clk_base + SCLK_BURST_POLICY, 0, 4, 0, 0, NULL);
-	clks[TEGRA20_CLK_SCLK] = clk;
-
 	/* twd */
 	clk = clk_register_fixed_factor(NULL, "twd", "cclk", 0, 1, 4);
 	clks[TEGRA20_CLK_TWD] = clk;
@@ -1014,7 +1010,7 @@ static struct tegra_cpu_car_ops tegra20_cpu_car_ops = {
 #endif
 };
 
-static struct tegra_clk_init_table init_table[] __initdata = {
+static struct tegra_clk_init_table init_table[] = {
 	{ TEGRA20_CLK_PLL_P, TEGRA20_CLK_CLK_MAX, 216000000, 1 },
 	{ TEGRA20_CLK_PLL_P_OUT1, TEGRA20_CLK_CLK_MAX, 28800000, 1 },
 	{ TEGRA20_CLK_PLL_P_OUT2, TEGRA20_CLK_CLK_MAX, 48000000, 1 },
@@ -1052,11 +1048,6 @@ static struct tegra_clk_init_table init_table[] __initdata = {
 	{ TEGRA20_CLK_CLK_MAX, TEGRA20_CLK_CLK_MAX, 0, 0 },
 };
 
-static void __init tegra20_clock_apply_init_table(void)
-{
-	tegra_init_from_table(init_table, clks, TEGRA20_CLK_CLK_MAX);
-}
-
 /*
  * Some clocks may be used by different drivers depending on the board
  * configuration.  List those here to register them twice in the clock lookup
@@ -1076,6 +1067,8 @@ static const struct of_device_id pmc_match[] __initconst = {
 	{ },
 };
 
+static bool tegra20_car_initialized;
+
 static struct clk *tegra20_clk_src_onecell_get(struct of_phandle_args *clkspec,
 					       void *data)
 {
@@ -1083,6 +1076,16 @@ static struct clk *tegra20_clk_src_onecell_get(struct of_phandle_args *clkspec,
 	struct clk_hw *hw;
 	struct clk *clk;
 
+	/*
+	 * Timer clocks are needed early, the rest of the clocks shouldn't be
+	 * available to device drivers until clock tree is fully initialized.
+	 */
+	if (clkspec->args[0] != TEGRA20_CLK_RTC &&
+	    clkspec->args[0] != TEGRA20_CLK_TWD &&
+	    clkspec->args[0] != TEGRA20_CLK_TIMER &&
+	    !tegra20_car_initialized)
+		return ERR_PTR(-EPROBE_DEFER);
+
 	clk = of_clk_src_onecell_get(clkspec, data);
 	if (IS_ERR(clk))
 		return clk;
@@ -1149,10 +1152,48 @@ static void __init tegra20_clock_init(struct device_node *np)
 	tegra_init_dup_clks(tegra_clk_duplicates, clks, TEGRA20_CLK_CLK_MAX);
 
 	tegra_add_of_provider(np, tegra20_clk_src_onecell_get);
-	tegra_register_devclks(devclks, ARRAY_SIZE(devclks));
-
-	tegra_clk_apply_init_table = tegra20_clock_apply_init_table;
 
 	tegra_cpu_car_ops = &tegra20_cpu_car_ops;
 }
-CLK_OF_DECLARE(tegra20, "nvidia,tegra20-car", tegra20_clock_init);
+CLK_OF_DECLARE_DRIVER(tegra20, "nvidia,tegra20-car", tegra20_clock_init);
+
+/*
+ * Clocks that use runtime PM can't be created at the tegra20_clock_init
+ * time because drivers' base isn't initialized yet, and thus platform
+ * devices can't be created for the clocks.  Hence we need to split the
+ * registration of the clocks into two phases.  The first phase registers
+ * essential clocks which don't require RPM and are actually used during
+ * early boot.  The second phase registers clocks which use RPM and this
+ * is done when device drivers' core API is ready.
+ */
+static int tegra20_car_probe(struct platform_device *pdev)
+{
+	struct clk *clk;
+
+	clk = tegra_clk_register_super_mux("sclk", sclk_parents,
+			      ARRAY_SIZE(sclk_parents),
+			      CLK_SET_RATE_PARENT | CLK_IS_CRITICAL,
+			      clk_base + SCLK_BURST_POLICY, 0, 4, 0, 0, NULL);
+	clks[TEGRA20_CLK_SCLK] = clk;
+
+	tegra_register_devclks(devclks, ARRAY_SIZE(devclks));
+	tegra_init_from_table(init_table, clks, TEGRA20_CLK_CLK_MAX);
+	tegra20_car_initialized = true;
+
+	return 0;
+}
+
+static const struct of_device_id tegra20_car_match[] = {
+	{ .compatible = "nvidia,tegra20-car" },
+	{ }
+};
+
+static struct platform_driver tegra20_car_driver = {
+	.driver = {
+		.name = "tegra20-car",
+		.of_match_table = tegra20_car_match,
+		.suppress_bind_attrs = true,
+	},
+	.probe = tegra20_car_probe,
+};
+builtin_platform_driver(tegra20_car_driver);