USB: serial: add macro for console error reporting

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@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 15 insertions, 0 deletions

diff --git a/include/linux/usb/serial.h b/include/linux/usb/serial.h
index 4267a9c717ba..10cb74d2ad1d 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 */