[08/16] serial: mvebu-uart: clear state register before IRQ request

Message ID 20171006101344.15590-9-miquel.raynal@free-electrons.com
State New
Headers show
Series
  • Support armada-37xx second UART port
Related show

Commit Message

Miquel RAYNAL Oct. 6, 2017, 10:13 a.m.
From: Allen Yan <yanwei@marvell.com>

When receiving data on RX pin before ->uart_startup() is called, some
error bits in the state register could be set up (like BRK_DET).

This is harmless when using only the standard UART (error bits are
read-only), but may procude an endless loop once in the extended UART
RX interrupt handler (error bits must be cleared).

Clear the status register in ->uart_startup() to avoid this situation.

Signed-off-by: Allen Yan <yanwei@marvell.com>
Signed-off-by: Miquel Raynal <miquel.raynal@free-electrons.com>
---
 drivers/tty/serial/mvebu-uart.c | 6 ++++++
 1 file changed, 6 insertions(+)

Comments

Gregory CLEMENT Oct. 6, 2017, 12:40 p.m. | #1
Hi Miquel,
 
 On ven., oct. 06 2017, Miquel Raynal <miquel.raynal@free-electrons.com> wrote:

> From: Allen Yan <yanwei@marvell.com>
>
> When receiving data on RX pin before ->uart_startup() is called, some
> error bits in the state register could be set up (like BRK_DET).
>
> This is harmless when using only the standard UART (error bits are
> read-only), but may procude an endless loop once in the extended UART
                      produce
> RX interrupt handler (error bits must be cleared).
>
> Clear the status register in ->uart_startup() to avoid this situation.
>
> Signed-off-by: Allen Yan <yanwei@marvell.com>
> Signed-off-by: Miquel Raynal <miquel.raynal@free-electrons.com>

Reviewed-by: Gregory CLEMENT <gregory.clement@free-electrons.com>

Thanks,

Gregory


> ---
>  drivers/tty/serial/mvebu-uart.c | 6 ++++++
>  1 file changed, 6 insertions(+)
>
> diff --git a/drivers/tty/serial/mvebu-uart.c b/drivers/tty/serial/mvebu-uart.c
> index 81a3d2714fd3..67f302748b78 100644
> --- a/drivers/tty/serial/mvebu-uart.c
> +++ b/drivers/tty/serial/mvebu-uart.c
> @@ -322,6 +322,12 @@ static int mvebu_uart_startup(struct uart_port *port)
>  	writel(CTRL_TXFIFO_RST | CTRL_RXFIFO_RST,
>  	       port->membase + UART_CTRL(port));
>  	udelay(1);
> +
> +	/* Clear the error bits of state register before IRQ request */
> +	ret = readl(port->membase + UART_STAT);
> +	ret |= STAT_BRK_ERR;
> +	writel(ret, port->membase + UART_STAT);
> +
>  	writel(CTRL_BRK_INT, port->membase + UART_CTRL(port));
>  
>  	ctl = readl(port->membase + UART_INTR(port));
> -- 
> 2.11.0
>
>
> _______________________________________________
> linux-arm-kernel mailing list
> linux-arm-kernel@lists.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

Patch

diff --git a/drivers/tty/serial/mvebu-uart.c b/drivers/tty/serial/mvebu-uart.c
index 81a3d2714fd3..67f302748b78 100644
--- a/drivers/tty/serial/mvebu-uart.c
+++ b/drivers/tty/serial/mvebu-uart.c
@@ -322,6 +322,12 @@  static int mvebu_uart_startup(struct uart_port *port)
 	writel(CTRL_TXFIFO_RST | CTRL_RXFIFO_RST,
 	       port->membase + UART_CTRL(port));
 	udelay(1);
+
+	/* Clear the error bits of state register before IRQ request */
+	ret = readl(port->membase + UART_STAT);
+	ret |= STAT_BRK_ERR;
+	writel(ret, port->membase + UART_STAT);
+
 	writel(CTRL_BRK_INT, port->membase + UART_CTRL(port));
 
 	ctl = readl(port->membase + UART_INTR(port));