soc: apple: rtkit: Add apple_rtkit_poll

This allows a client to receive messages in atomic context, by polling.
Signed-off-by: Hector Martin <marcan@marcan.st>
Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Reviewed-by: Sven Peter <sven@svenpeter.dev>
Reviewed-by: Eric Curtin <ecurtin@redhat.com>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>

drivers/soc/apple/rtkit.c

@@ -660,6 +660,12 @@ int apple_rtkit_send_message_wait(struct apple_rtkit *rtk, u8 ep, u64 message,
 }
 EXPORT_SYMBOL_GPL(apple_rtkit_send_message_wait);
 
+int apple_rtkit_poll(struct apple_rtkit *rtk)
+{
+	return mbox_client_peek_data(rtk->mbox_chan);
+}
+EXPORT_SYMBOL_GPL(apple_rtkit_poll);
+
 int apple_rtkit_start_ep(struct apple_rtkit *rtk, u8 endpoint)
 {
 	u64 msg;

include/linux/soc/apple/rtkit.h

@@ -152,4 +152,16 @@ int apple_rtkit_send_message(struct apple_rtkit *rtk, u8 ep, u64 message,
 int apple_rtkit_send_message_wait(struct apple_rtkit *rtk, u8 ep, u64 message,
 				  unsigned long timeout, bool atomic);
 
+/*
+ * Process incoming messages in atomic context.
+ * This only guarantees that messages arrive as far as the recv_message_early
+ * callback; drivers expecting to handle incoming messages synchronously
+ * by calling this function must do it that way.
+ * Will return 1 if some data was processed, 0 if none was, or a
+ * negative error code on failure.
+ *
+ * @rtk:            RTKit reference
+ */
+int apple_rtkit_poll(struct apple_rtkit *rtk);
+
 #endif /* _LINUX_APPLE_RTKIT_H_ */