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

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Message-ID: <d727b350-7936-2671-45c2-cf32dfda1a2a@baylibre.com>
Date:   Fri, 20 Oct 2017 10:10:42 +0200
From:   Neil Armstrong <narmstrong@...libre.com>
To:     Yixun Lan <dlan@...too.org>, Kevin Hilman <khilman@...libre.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     linux-kernel@...r.kernel.org,
        Ben Dooks <ben.dooks@...ethink.co.uk>,
        linux-serial@...r.kernel.org, linux-amlogic@...ts.infradead.org,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v2] serial: meson: add Magic SysRq support

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@...too.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);
>  
> 

Reviewed-by: Neil Armstrong <narmstrong@...libre.com>