Re: [PATCH v2] serial: meson: add Magic SysRq support

From: Neil Armstrong
Date: Fri Oct 20 2017 - 04:10:55 EST


Hi Yixun,

On 06/09/2017 15:52, Yixun Lan wrote:
> This dirver try to implement the Magic SysRq support[1] for
> Amlogic Inc's meson platfo

Please fix these typos.

> 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@xxxxxxxxxx>
>
> ---
> 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);
>
>

Reviewed-by: Neil Armstrong <narmstrong@xxxxxxxxxxxx>