[PATCH v4 3/3] firmware: xilinx: Clear firmware notifiers across kexec transitions

[Jay Buddhabhatti]

During a kexec restart, only the kernel is reloaded but notifier callbacks
in firmware persist, causing state mismatches between kernel and firmware.

To address this, introduce PM_ALL_NOTIFIERS node ID to unregister all
notifier callbacks during kexec. On a graceful kexec restart, this occurs
in zynqmp_firmware_shutdown(). On a crash kernel restart, it happens in
zynqmp_firmware_probe() in the reloaded kernel.

Unregistering all notifiers depends on firmware support for the
PM_ALL_NOTIFIERS node ID. On firmware that does not implement it (the
feature check reports a version below PM_API_VERSION_3) the step is
skipped and a warning such as "Firmware doesn't support unregister all
notifiers at once" is logged, e.g. on Versal NET firmware that predates
this API.

Signed-off-by: Jay Buddhabhatti <jay.buddhabhatti at amd.com>
Reviewed-by: Radhey Shyam Pandey <radhey.shyam.pandey at amd.com>
Reviewed-by: Prasanna Kumar T S M <ptsm at linux.microsoft.com>
---
 drivers/firmware/xilinx/zynqmp.c     | 14 ++++++++++++++
 include/linux/firmware/xlnx-zynqmp.h |  3 +++
 2 files changed, 17 insertions(+)

diff --git a/drivers/firmware/xilinx/zynqmp.c b/drivers/firmware/xilinx/zynqmp.c
index 28bcf3a1e6db..89380cadc8e4 100644
--- a/drivers/firmware/xilinx/zynqmp.c
+++ b/drivers/firmware/xilinx/zynqmp.c
@@ -2112,6 +2112,20 @@ static int zynqmp_clear_pm_state(struct device *dev)
 				 "Bulk device release is not supported by firmware: %d\n", ret);
 			ret = 0;
 		}
+
+		/* Check if the firmware supports the PM_ALL_NOTIFIERS node ID */
+		ret = do_feature_check_call(PM_REGISTER_NOTIFIER);
+		if (ret >= 0 && ((ret & FIRMWARE_VERSION_MASK) >= PM_API_VERSION_3)) {
+			/* Attempt to unregister all notifier callbacks via firmware */
+			ret = zynqmp_pm_register_notifier(PM_ALL_NOTIFIERS, 0, 0, 0);
+			if (ret)
+				dev_err(dev, "Failed to unregister all notifiers: %d\n", ret);
+		} else {
+			dev_warn(dev,
+				 "Firmware doesn't support unregister all notifiers at once: %d\n",
+				 ret);
+			ret = 0;
+		}
 	}
 
 	return ret;
diff --git a/include/linux/firmware/xlnx-zynqmp.h b/include/linux/firmware/xlnx-zynqmp.h
index ac39e5492961..69a2f74269f3 100644
--- a/include/linux/firmware/xlnx-zynqmp.h
+++ b/include/linux/firmware/xlnx-zynqmp.h
@@ -149,6 +149,9 @@
 /* Node ID for all peripheral devices */
 #define PM_DEV_ALL_PERIPH	0x18224FFFU
 
+/* Node ID for all notifier callbacks */
+#define PM_ALL_NOTIFIERS	0xFFFFFFFFU
+
 enum pm_module_id {
 	PM_MODULE_ID = 0x0,
 	XPM_MODULE_ID = 0x2,
-- 
2.34.1