From: Nathan Lynch <redacted>

Use the function lock API to prevent interleaving call sequences of
the ibm,activate-firmware RTAS function, which typically requires
multiple calls to complete the update. While the spec does not
specifically prohibit interleaved sequences, there's almost certainly
no advantage to allowing them.

Signed-off-by: Nathan Lynch <redacted>
---
 arch/powerpc/kernel/rtas.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/arch/powerpc/kernel/rtas.c b/arch/powerpc/kernel/rtas.c
index 52f2242d0c28..e38ba05ad613 100644
--- a/arch/powerpc/kernel/rtas.c
+++ b/arch/powerpc/kernel/rtas.c

@@ -1753,10 +1753,14 @@ void rtas_activate_firmware(void)
 		return;
 	}
 
+	rtas_function_lock(RTAS_FN_IBM_ACTIVATE_FIRMWARE);
+
 	do {
 		fwrc = rtas_call(token, 0, 1, NULL);
 	} while (rtas_busy_delay(fwrc));
 
+	rtas_function_unlock(RTAS_FN_IBM_ACTIVATE_FIRMWARE);
+
 	if (fwrc)
 		pr_err("ibm,activate-firmware failed (%i)\n", fwrc);
 }

-- 
2.41.0