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Subject[PATCH v2] serial: meson: add Magic SysRq support
Date
This dirver try to implement the Magic SysRq support[1] for
Amlogic Inc's meson platfo
From the hardware perspective, the UART IP can't detect the 'BREAK' command
clearly via the status register. Instead, we rely on the combination of
'FRAME_ERR bit && ch == 0', and it works fine.

[1] Documentation/admin-guide/sysrq.rst

Signed-off-by: Yixun Lan <dlan@gentoo.org>

---
Changes since v1 at [0]:
- add changelog & a few more comments

[0] https://patchwork.kernel.org/patch/9728475/
---
drivers/tty/serial/meson_uart.c | 18 ++++++++++++++++--
1 file changed, 16 insertions(+), 2 deletions(-)

diff --git a/drivers/tty/serial/meson_uart.c b/drivers/tty/serial/meson_uart.c
index 42e4a4c7597f..3fea24bafd80 100644
--- a/drivers/tty/serial/meson_uart.c
+++ b/drivers/tty/serial/meson_uart.c
@@ -14,6 +14,10 @@
*
*/

+#if defined(CONFIG_SERIAL_MESON_CONSOLE) && defined(CONFIG_MAGIC_SYSRQ)
+#define SUPPORT_SYSRQ
+#endif
+
#include <linux/clk.h>
#include <linux/console.h>
#include <linux/delay.h>
@@ -183,12 +187,12 @@ static void meson_receive_chars(struct uart_port *port)
{
struct tty_port *tport = &port->state->port;
char flag;
- u32 status, ch, mode;
+ u32 ostatus, status, ch, mode;

do {
flag = TTY_NORMAL;
port->icount.rx++;
- status = readl(port->membase + AML_UART_STATUS);
+ ostatus = status = readl(port->membase + AML_UART_STATUS);

if (status & AML_UART_ERR) {
if (status & AML_UART_TX_FIFO_WERR)
@@ -216,6 +220,16 @@ static void meson_receive_chars(struct uart_port *port)
ch = readl(port->membase + AML_UART_RFIFO);
ch &= 0xff;

+ if ((ostatus & AML_UART_FRAME_ERR) && (ch == 0)) {
+ port->icount.brk++;
+ flag = TTY_BREAK;
+ if (uart_handle_break(port))
+ continue;
+ }
+
+ if (uart_handle_sysrq_char(port, ch))
+ continue;
+
if ((status & port->ignore_status_mask) == 0)
tty_insert_flip_char(tport, ch, flag);

--
2.14.1
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