serial: 8250_uniphier: use CHAR register for canary to detect power-off

The 8250 core uses the SCR as a canary to discover if the console has
been powered-off.

This hardware does not have SCR at offset 7, but an unused register
CHAR at a different offset.  As long as the character interrupt is
disabled, the register access has no impact, so it is useful as an
alternative scratch register.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/tty/serial/8250/8250_uniphier.c b/drivers/tty/serial/8250/8250_uniphier.c
index 633ac378b7f26be7e24b43a9de6c7ce560322ba3..97a45b798fcd04ccded250fecbb3cb641d565f3d 100644 (file)
--- a/drivers/tty/serial/8250/8250_uniphier.c
+++ b/drivers/tty/serial/8250/8250_uniphier.c
@@ -29,12 +29,13 @@
  *   - MMIO32 (regshift = 2)
  *   - FCR is not at 2, but 3
  *   - LCR and MCR are not at 3 and 4, they share 4
+ *   - No SCR (Instead, CHAR can be used as a scratch register)
  *   - Divisor latch at 9, no divisor latch access bit
  */
 
 #define UNIPHIER_UART_REGSHIFT         2
 
-/* bit[15:8] = CHAR (not used), bit[7:0] = FCR */
+/* bit[15:8] = CHAR, bit[7:0] = FCR */
 #define UNIPHIER_UART_CHAR_FCR         (3 << (UNIPHIER_UART_REGSHIFT))
 /* bit[15:8] = LCR, bit[7:0] = MCR */
 #define UNIPHIER_UART_LCR_MCR          (4 << (UNIPHIER_UART_REGSHIFT))
@@ -72,13 +73,18 @@ OF_EARLYCON_DECLARE(uniphier, "socionext,uniphier-uart",
 
 /*
  * The register map is slightly different from that of 8250.
- * IO callbacks must be overridden for correct access to FCR, LCR, and MCR.
+ * IO callbacks must be overridden for correct access to FCR, LCR, MCR and SCR.
  */
 static unsigned int uniphier_serial_in(struct uart_port *p, int offset)
 {
        unsigned int valshift = 0;
 
        switch (offset) {
+       case UART_SCR:
+               /* No SCR for this hardware.  Use CHAR as a scratch register */
+               valshift = 8;
+               offset = UNIPHIER_UART_CHAR_FCR;
+               break;
        case UART_LCR:
                valshift = 8;
                /* fall through */
@@ -91,8 +97,8 @@ static unsigned int uniphier_serial_in(struct uart_port *p, int offset)
        }
 
        /*
-        * The return value must be masked with 0xff because LCR and MCR reside
-        * in the same register that must be accessed by 32-bit write/read.
+        * The return value must be masked with 0xff because some registers
+        * share the same offset that must be accessed by 32-bit write/read.
         * 8 or 16 bit access to this hardware result in unexpected behavior.
         */
        return (readl(p->membase + offset) >> valshift) & 0xff;
@@ -101,9 +107,13 @@ static unsigned int uniphier_serial_in(struct uart_port *p, int offset)
 static void uniphier_serial_out(struct uart_port *p, int offset, int value)
 {
        unsigned int valshift = 0;
-       bool normal = true;
+       bool normal = false;
 
        switch (offset) {
+       case UART_SCR:
+               /* No SCR for this hardware.  Use CHAR as a scratch register */
+               valshift = 8;
+               /* fall through */
        case UART_FCR:
                offset = UNIPHIER_UART_CHAR_FCR;
                break;
@@ -114,10 +124,10 @@ static void uniphier_serial_out(struct uart_port *p, int offset, int value)
                /* fall through */
        case UART_MCR:
                offset = UNIPHIER_UART_LCR_MCR;
-               normal = false;
                break;
        default:
                offset <<= UNIPHIER_UART_REGSHIFT;
+               normal = true;
                break;
        }