[PATCH] power-domain: fix hang in endless loop on i.MX8

[Anatolij Gustschin]

Currently when booting the kernel on i.MX8 U-Boot hangs in an
endless loop when switching off dma, connectivity or lsio power
domains during device removal. It hapens first when removing
gpio0 (gpio at 5d080000) device, here its power domain device
'lsio_gpio0' is obtained for switching off power. Since the
obtained 'lsio_gpio0' device is removed afterwards, its power
domain is also switched off and here the parent power domain
device 'lsio_power_domain' is optained for switching off the
power. Thereafter, when the obtained 'lsio_power_domain' is
removed, device_remove() removes its first child 'lsio_gpio0'.
During this child removal the 'lsio_power_domain' device is
obtained again for switching and when removing it later,
the same child removal is repeated, so we are stuck in an
endless loop. Below is a snippet from dm tree on i.MX8QXP
for better illustration of the DM devices relationship:

 Class     Index  Probed  Driver                Name
-----------------------------------------------------------
 root          0  [ + ]   root_driver           root_driver
...
 simple_bus    0  [ + ]   generic_simple_bus    |-- imx8qx-pm
 power_doma    0  [ + ]   imx8_power_domain     |   |-- lsio_power_domain
 power_doma    1  [ + ]   imx8_power_domain     |   |   |-- lsio_gpio0
 power_doma    2  [ + ]   imx8_power_domain     |   |   |-- lsio_gpio1

Do not remove a power domain device if it is a parent of the
currently controlled device.

Fixes: 52edfed65de9 ("dm: core: device: switch off power domain after device removal")
Signed-off-by: Anatolij Gustschin <agust at denx.de>
Reported-by: Oliver Graute <oliver.graute at gmail.com>
Reported-by: Fabio Estevam <festevam at gmail.com>

---
 drivers/power/domain/power-domain-uclass.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/drivers/power/domain/power-domain-uclass.c b/drivers/power/domain/power-domain-uclass.c
index d9c623b56e..d8fe4d4877 100644
--- a/drivers/power/domain/power-domain-uclass.c
+++ b/drivers/power/domain/power-domain-uclass.c
@@ -127,6 +127,18 @@ static int dev_power_domain_ctrl(struct udevice *dev, bool on)
 			ret = power_domain_off(&pd);
 	}
 
+	/*
+	 * For platforms with parent and child power-domain devices
+	 * we may not run device_remove() on the power-domain parent
+	 * because it will result in removing its children and switching
+	 * off their power-domain parent. So we will get here again and
+	 * again and will be stuck in an endless loop.
+	 */
+	if (!on && dev_get_parent(dev) == pd.dev &&
+	    device_get_uclass_id(dev) == UCLASS_POWER_DOMAIN) {
+		return ret;
+	}
+
 	/*
 	 * power_domain_get() bound the device, thus
 	 * we must remove it again to prevent unbinding
-- 
2.17.1