[PATCH 1/3 v2] USB: serial: add macro for console error reporting

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Add macro which prints an error message only once if port is used a
console.

Reporting errors in a write path when port is used as a console could
otherwise result in an infinite loop.

Signed-off-by: Johan Hovold <jhovold@xxxxxxxxx>
---

v2: add missing do { } while (0)


 include/linux/usb/serial.h |   15 +++++++++++++++
 1 files changed, 15 insertions(+), 0 deletions(-)

diff --git a/include/linux/usb/serial.h b/include/linux/usb/serial.h
index 4267a9c..0cd7814 100644
--- a/include/linux/usb/serial.h
+++ b/include/linux/usb/serial.h
@@ -389,5 +389,20 @@ do {									\
 		printk(KERN_DEBUG "%s: " format "\n", __FILE__, ##arg);	\
 } while (0)
 
+/*
+ * Macro for reporting errors in write path to avoid inifinite loop
+ * when port is used as a console.
+ */
+#define dev_err_console(usport, fmt, ...)				\
+do {									\
+	static bool __print_once;					\
+	struct usb_serial_port *port = (usport);			\
+									\
+	if (!port->port.console || !__print_once) {			\
+		__print_once = true;					\
+		dev_err(&port->dev, fmt, ##__VA_ARGS__);		\
+	}								\
+} while (0)
+
 #endif /* __LINUX_USB_SERIAL_H */
 
-- 
1.7.8.4

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