[RFC PATCH 3/9] pmdomain/rockchip: cycle optional power-domain resets on power-on

[Jiaxing Hu <gahing@gahingwoo.com>]

Some power domains contain hardware bus interfaces that require an
explicit assert/deassert edge on their reset line after the domain
is powered on.  The CRU preserves reset state across power cycles
(stays deasserted), so the hardware never sees the edge it needs to
initialize unless the driver pulses it explicitly.

Add an optional resets property to rockchip_pm_domain.  When present,
the resets are asserted and deasserted (with a 10 µs hold) inside
rockchip_pd_power() after the idle bits are cleared and the
delay_us settling time has elapsed, but before any device in the
domain resumes.  This ordering guarantees the bus is fully
initialized before any device driver accesses registers.

Signed-off-by: Jiaxing Hu <gahing@gahingwoo.com>
---
 drivers/pmdomain/rockchip/pm-domains.c | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/drivers/pmdomain/rockchip/pm-domains.c b/drivers/pmdomain/rockchip/pm-domains.c
index 1787f62ba..7a88a9149 100644
--- a/drivers/pmdomain/rockchip/pm-domains.c
+++ b/drivers/pmdomain/rockchip/pm-domains.c
@@ -18,6 +18,7 @@
 #include <linux/of_address.h>
 #include <linux/of_clk.h>
 #include <linux/clk.h>
+#include <linux/reset.h>
 #include <linux/regmap.h>
 #include <linux/regulator/consumer.h>
 #include <linux/mfd/syscon.h>
@@ -102,6 +103,7 @@ struct rockchip_pm_domain {
 	struct clk_bulk_data *clks;
 	struct device_node *node;
 	struct regulator *supply;
+	struct reset_control *resets;
 };
 
 struct rockchip_pmu {
@@ -671,6 +673,12 @@ static int rockchip_pd_power(struct rockchip_pm_domain *pd, bool power_on)
 		if (pd->info->delay_us)
 			udelay(pd->info->delay_us);
 
+		if (pd->resets) {
+			reset_control_assert(pd->resets);
+			udelay(10);
+			reset_control_deassert(pd->resets);
+		}
+
 		rockchip_pmu_restore_qos(pd);
 	}
 
@@ -840,6 +848,14 @@ static int rockchip_pm_add_one_domain(struct rockchip_pmu *pmu,
 	if (error)
 		goto err_put_clocks;
 
+	pd->resets = of_reset_control_array_get_optional_exclusive(node);
+	if (IS_ERR(pd->resets)) {
+		error = PTR_ERR(pd->resets);
+		dev_err(pmu->dev, "%pOFn: failed to get resets: %d\n", node, error);
+		pd->resets = NULL;
+		goto err_unprepare_clocks;
+	}
+
 	pd->num_qos = of_count_phandle_with_args(node, "pm_qos",
 						 NULL);
 
@@ -910,6 +926,7 @@ static int rockchip_pm_add_one_domain(struct rockchip_pmu *pmu,
 	clk_bulk_unprepare(pd->num_clks, pd->clks);
 err_put_clocks:
 	clk_bulk_put(pd->num_clks, pd->clks);
+	reset_control_put(pd->resets);
 	return error;
 }
 
-- 
2.43.0