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serial: meson: add Magic SysRq support 

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
hifive-unleashed-5.1
Yixun Lan 2017-09-06 21:52:39 +08:00 committed by Greg Kroah-Hartman
parent 2bd6bf03f4
commit b86ac22503
1 changed files with 16 additions and 2 deletions
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18
drivers/tty/serial/meson_uart.c
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@ -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);