[PATCH v4 2/4] firmware: arm_sdei: add SDEI_EVENT_SIGNAL support

[Kiryl Shutsemau <kirill@shutemov.name>]

From: "Kiryl Shutsemau (Meta)" <kas@kernel.org>

Add sdei_event_signal(), a thin wrapper over the SDEI_EVENT_SIGNAL call
(DEN0054) that makes the software-signalled event (event 0) pending on a
target PE -- delivered NMI-like even when that PE has interrupts masked.
It takes no locks, so it is safe to call from NMI / crash context.

Signed-off-by: Kiryl Shutsemau (Meta) <kas@kernel.org>
Reviewed-by: Douglas Anderson <dianders@chromium.org>
---
 drivers/firmware/arm_sdei.c   | 12 ++++++++++++
 include/linux/arm_sdei.h      |  6 ++++++
 include/uapi/linux/arm_sdei.h |  1 +
 3 files changed, 19 insertions(+)

diff --git a/drivers/firmware/arm_sdei.c b/drivers/firmware/arm_sdei.c
index c161cf263547..e8dd2f0f3919 100644
--- a/drivers/firmware/arm_sdei.c
+++ b/drivers/firmware/arm_sdei.c
@@ -339,6 +339,18 @@ static void _ipi_unmask_cpu(void *ignored)
 	sdei_unmask_local_cpu();
 }
 
+/*
+ * Signal the software-signalled event (event 0) to @mpidr. Does nothing
+ * but the SMC -- no locks, no event lookup -- so it is safe from NMI /
+ * crash context (e.g. the cross-CPU NMI service).
+ */
+int sdei_event_signal(u32 event_num, u64 mpidr)
+{
+	return invoke_sdei_fn(SDEI_1_0_FN_SDEI_EVENT_SIGNAL, event_num,
+			      mpidr, 0, 0, 0, NULL);
+}
+NOKPROBE_SYMBOL(sdei_event_signal);
+
 /*
  * Was SDEI firmware probed and is it usable?  Lets optional consumers skip
  * registering an event -- and the warning a failed registration emits -- on
diff --git a/include/linux/arm_sdei.h b/include/linux/arm_sdei.h
index b07113eeeff7..b9dc21c241be 100644
--- a/include/linux/arm_sdei.h
+++ b/include/linux/arm_sdei.h
@@ -37,6 +37,12 @@ int sdei_event_unregister(u32 event_num);
 int sdei_event_enable(u32 event_num);
 int sdei_event_disable(u32 event_num);
 
+/*
+ * Signal the software-signalled event (event 0) to another PE, NMI-like.
+ * @mpidr is the target's MPIDR affinity.
+ */
+int sdei_event_signal(u32 event_num, u64 mpidr);
+
 /* Was SDEI firmware probed and usable? */
 bool sdei_is_present(void);
 
diff --git a/include/uapi/linux/arm_sdei.h b/include/uapi/linux/arm_sdei.h
index af0630ba5437..22eb61612673 100644
--- a/include/uapi/linux/arm_sdei.h
+++ b/include/uapi/linux/arm_sdei.h
@@ -22,6 +22,7 @@
 #define SDEI_1_0_FN_SDEI_PE_UNMASK			SDEI_1_0_FN(0x0C)
 #define SDEI_1_0_FN_SDEI_INTERRUPT_BIND			SDEI_1_0_FN(0x0D)
 #define SDEI_1_0_FN_SDEI_INTERRUPT_RELEASE		SDEI_1_0_FN(0x0E)
+#define SDEI_1_0_FN_SDEI_EVENT_SIGNAL			SDEI_1_0_FN(0x0F)
 #define SDEI_1_0_FN_SDEI_PRIVATE_RESET			SDEI_1_0_FN(0x11)
 #define SDEI_1_0_FN_SDEI_SHARED_RESET			SDEI_1_0_FN(0x12)
 
-- 
2.54.0