[PATCH 4/6] soc/tegra: pmc: Add an option to keep the VDE partition on

[Artur Kowalski <arturkow2000@gmail.com>]

After a warm reset, which doesn't reset the PMC, Tegra20's boot ROM
hangs if the VDE partition is powered off. The driver powers the
partition off when it registers it, and genpd powers it off whenever
the VDE is idle. The VDE driver powers it on again when the system
shuts down, since commit 8f0c714ad9be ("media: staging: tegra-vde: Turn
ON power domain on shutdown"), which covers regular reboots. A watchdog
reset doesn't go through the shutdown, so it still hangs the system
instead of rebooting it.

Add the vde_always_on module parameter, which keeps the partition
powered on, at the cost of its idle power. Instead of powering the
partition off when registering it, the driver runs the power up
sequence on it, which puts its clocks, resets and clamps into the same
known state without cutting its power, and registers its genpd as
always on. tegra_powergate_set() also doesn't power it off, which
covers the legacy power gating API.

Assisted-by: Claude:claude-opus-5-5
Signed-off-by: Artur Kowalski <arturkow2000@gmail.com>
---
 Documentation/admin-guide/kernel-parameters.txt | 12 ++++++
 drivers/soc/tegra/pmc.c                         | 54 +++++++++++++++++++++++--
 2 files changed, 62 insertions(+), 4 deletions(-)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 0b3c140babd9..81af8aa1482a 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -7571,6 +7571,18 @@ Kernel parameters
 
 	tdfx=		[HW,DRM]
 
+	tegra_pmc.vde_always_on=
+			[HW,ARM] Never power off the VDE power partition.
+			After a warm reset, which doesn't reset the PMC, the
+			boot ROM of Tegra20 hangs if the partition is off.
+			The VDE driver powers it on when the system shuts
+			down for a regular reboot, but a watchdog reset
+			doesn't go through the shutdown and hangs. Keeping
+			the partition on makes watchdog resets work, at the
+			cost of its idle power.
+			Format: <bool>
+			Default: false
+
 	test_suspend=	[SUSPEND]
 			Format: { "mem" | "standby" | "freeze" }[,N]
 			Specify "mem" (for Suspend-to-RAM) or "standby" (for
diff --git a/drivers/soc/tegra/pmc.c b/drivers/soc/tegra/pmc.c
index 2c70eedf514e..807977f52449 100644
--- a/drivers/soc/tegra/pmc.c
+++ b/drivers/soc/tegra/pmc.c
@@ -522,6 +522,28 @@ static struct tegra_pmc *early_pmc = &(struct tegra_pmc) {
 };
 #endif
 
+#ifdef MODULE_PARAM_PREFIX
+#undef MODULE_PARAM_PREFIX
+#endif
+#define MODULE_PARAM_PREFIX "tegra_pmc."
+
+/*
+ * After a warm reset, which doesn't reset the PMC, Tegra20's boot ROM hangs if
+ * the VDE partition is powered off. The VDE driver powers it on at shutdown,
+ * but a watchdog reset doesn't go through the shutdown and hangs. Keeping the
+ * partition powered on makes watchdog resets work, at the cost of its idle
+ * power.
+ */
+static bool vde_always_on;
+module_param(vde_always_on, bool, 0444);
+MODULE_PARM_DESC(vde_always_on,
+		 "Never power off the VDE partition (default: false)");
+
+static bool tegra_powergate_is_always_on(unsigned int id)
+{
+	return vde_always_on && id == TEGRA_POWERGATE_VDEC;
+}
+
 static inline struct tegra_powergate *
 to_powergate(struct generic_pm_domain *domain)
 {
@@ -697,6 +719,10 @@ static int tegra_powergate_set(struct tegra_pmc *pmc, unsigned int id,
 	if (id == TEGRA_POWERGATE_3D && pmc->soc->has_gpu_clamps)
 		return -EINVAL;
 
+	/* the partition is kept powered, also against the legacy API */
+	if (!new_state && tegra_powergate_is_always_on(id))
+		return 0;
+
 	mutex_lock(&pmc->powergates_lock);
 
 	if (tegra_powergate_state(pmc, id) == new_state) {
@@ -1319,6 +1345,7 @@ static int tegra_powergate_add(struct tegra_pmc *pmc, struct device_node *np)
 	struct device *dev = pmc->dev;
 	struct tegra_powergate *pg;
 	int id, err = 0;
+	bool always_on;
 	bool off;
 
 	pg = kzalloc_obj(*pg);
@@ -1346,6 +1373,7 @@ static int tegra_powergate_add(struct tegra_pmc *pmc, struct device_node *np)
 	pg->pmc = pmc;
 
 	off = !tegra_powergate_is_powered(pmc, pg->id);
+	always_on = tegra_powergate_is_always_on(pg->id);
 
 	err = tegra_powergate_of_get_clks(pg, np);
 	if (err < 0) {
@@ -1363,9 +1391,20 @@ static int tegra_powergate_add(struct tegra_pmc *pmc, struct device_node *np)
 	 * If the power-domain is off, then ensure the resets are asserted.
 	 * If the power-domain is on, then power down to ensure that when is
 	 * it turned on the power-domain, clocks and resets are all in the
-	 * expected state.
+	 * expected state. A power-domain that is kept on is powered up instead,
+	 * which puts it into the same state without powering it off.
 	 */
-	if (off) {
+	if (always_on) {
+		err = tegra_powergate_power_up(pg, true);
+		if (err) {
+			dev_err(dev, "failed to turn on PM domain %s: %d\n",
+				pg->genpd.name, err);
+			goto remove_resets;
+		}
+
+		dev_info(dev, "keeping PM domain %s powered on\n",
+			 pg->genpd.name);
+	} else if (off) {
 		err = reset_control_assert(pg->reset);
 		if (err) {
 			pr_err("failed to assert resets: %d\n", err);
@@ -1385,11 +1424,18 @@ static int tegra_powergate_add(struct tegra_pmc *pmc, struct device_node *np)
 	 * the domain and skip the genpd registration.
 	 */
 	if (!IS_ENABLED(CONFIG_PM_GENERIC_DOMAINS)) {
-		WARN_ON(tegra_powergate_power_up(pg, true));
+		if (!always_on)
+			WARN_ON(tegra_powergate_power_up(pg, true));
 		goto remove_resets;
 	}
 
-	err = pm_genpd_init(&pg->genpd, NULL, true);
+	if (always_on) {
+		/* as tegra_genpd_power_on() does after powering up */
+		reset_control_release(pg->reset);
+		pg->genpd.flags |= GENPD_FLAG_ALWAYS_ON;
+	}
+
+	err = pm_genpd_init(&pg->genpd, NULL, !always_on);
 	if (err < 0) {
 		dev_err(dev, "failed to initialise PM domain %pOFn: %d\n", np,
 		       err);

-- 
2.56.0