serial: fsl_lpuart: handle break and make sysrq work

Although there is already sysrq characters handling, a break condition
was never detected. Add support for it.

The LPUART can't distinguish between a framing error and a break
condition. We assume it is a break if the received data is all zero.

Signed-off-by: Michael Walle <michael@walle.cc>
Link: https://lore.kernel.org/r/20210512141255.18277-6-michael@walle.cc
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/tty/serial/fsl_lpuart.c b/drivers/tty/serial/fsl_lpuart.c
index 72caa7a..baa96e6 100644 (file)
--- a/drivers/tty/serial/fsl_lpuart.c
+++ b/drivers/tty/serial/fsl_lpuart.c
@@ -910,6 +910,7 @@ static void lpuart32_rxint(struct lpuart_port *sport)
        unsigned int flg, ignored = 0;
        struct tty_port *port = &sport->port.state->port;
        unsigned long rx, sr;
+       bool is_break;
 
        spin_lock(&sport->port.lock);
 
@@ -924,14 +925,27 @@ static void lpuart32_rxint(struct lpuart_port *sport)
                rx = lpuart32_read(&sport->port, UARTDATA);
                rx &= UARTDATA_MASK;
 
+               /*
+                * The LPUART can't distinguish between a break and a framing error,
+                * thus we assume it is a break if the received data is zero.
+                */
+               is_break = (sr & UARTSTAT_FE) && !rx;
+
+               if (is_break && uart_handle_break(&sport->port))
+                       continue;
+
                if (uart_prepare_sysrq_char(&sport->port, rx))
                        continue;
 
                if (sr & (UARTSTAT_PE | UARTSTAT_OR | UARTSTAT_FE)) {
-                       if (sr & UARTSTAT_PE)
-                               sport->port.icount.parity++;
-                       else if (sr & UARTSTAT_FE)
+                       if (sr & UARTSTAT_PE) {
+                               if (is_break)
+                                       sport->port.icount.brk++;
+                               else
+                                       sport->port.icount.parity++;
+                       } else if (sr & UARTSTAT_FE) {
                                sport->port.icount.frame++;
+                       }
 
                        if (sr & UARTSTAT_OR)
                                sport->port.icount.overrun++;
@@ -944,15 +958,17 @@ static void lpuart32_rxint(struct lpuart_port *sport)
 
                        sr &= sport->port.read_status_mask;
 
-                       if (sr & UARTSTAT_PE)
-                               flg = TTY_PARITY;
-                       else if (sr & UARTSTAT_FE)
+                       if (sr & UARTSTAT_PE) {
+                               if (is_break)
+                                       flg = TTY_BREAK;
+                               else
+                                       flg = TTY_PARITY;
+                       } else if (sr & UARTSTAT_FE) {
                                flg = TTY_FRAME;
+                       }
 
                        if (sr & UARTSTAT_OR)
                                flg = TTY_OVERRUN;
-
-                       sport->port.sysrq = 0;
                }
 
                tty_insert_flip_char(port, rx, flg);