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Message-ID: <54522163.8030408@linaro.org>
Date: Thu, 30 Oct 2014 11:30:43 +0000
From: Daniel Thompson <daniel.thompson@...aro.org>
To: Stephen Boyd <sboyd@...eaurora.org>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>
CC: linux-kernel@...r.kernel.org, linux-arm-msm@...r.kernel.org,
linux-arm-kernel@...ts.infradead.org, linux-serial@...r.kernel.org,
Frank Rowand <frank.rowand@...ymobile.com>
Subject: Re: [PATCH 2/2] tty: serial: msm: Support sysrq on uartDM devices
On 29/10/14 18:14, Stephen Boyd wrote:
> To properly support sysrq on uartDM hardware we need to properly
> handle break characters. With the DM hardware the fifo can pack 4
> characters at a time, where a break is indicated by an all zero
> byte. Unfortunately, we can't differentiate between an all zero
> byte for a break and an all zero byte of data, so try and do as
> best we can. First unmask the RX break start interrupt and record
> the interrupt when it arrives. Then while processing the fifo,
> detect the break by searching for an all zero character as long
> as we recently received an RX break start interrupt. This should
> make sysrq work fairly well.
>
> Cc: Frank Rowand <frank.rowand@...ymobile.com>
> Cc: Daniel Thompson <daniel.thompson@...aro.org>
> Signed-off-by: Stephen Boyd <sboyd@...eaurora.org>
> ---
> drivers/tty/serial/msm_serial.c | 41 +++++++++++++++++++++++++++++++----------
> drivers/tty/serial/msm_serial.h | 2 ++
> 2 files changed, 33 insertions(+), 10 deletions(-)
>
> diff --git a/drivers/tty/serial/msm_serial.c b/drivers/tty/serial/msm_serial.c
> index cedcc36762a2..d44c04976f7a 100644
> --- a/drivers/tty/serial/msm_serial.c
> +++ b/drivers/tty/serial/msm_serial.c
> @@ -54,6 +54,7 @@ struct msm_port {
> unsigned int imr;
> int is_uartdm;
> unsigned int old_snap_state;
> + bool break_detected;
> };
>
> static inline void wait_for_xmitr(struct uart_port *port)
> @@ -126,23 +127,38 @@ static void handle_rx_dm(struct uart_port *port, unsigned int misr)
>
> while (count > 0) {
> unsigned char buf[4];
> + int sysrq, r_count, i;
>
> sr = msm_read(port, UART_SR);
> if ((sr & UART_SR_RX_READY) == 0) {
> msm_port->old_snap_state -= count;
> break;
> }
> +
> ioread32_rep(port->membase + UARTDM_RF, buf, 1);
> - if (sr & UART_SR_RX_BREAK) {
> - port->icount.brk++;
> - if (uart_handle_break(port))
> - continue;
> - } else if (sr & UART_SR_PAR_FRAME_ERR)
> - port->icount.frame++;
> + r_count = min_t(int, count, sizeof(buf));
> +
> + for (i = 0; i < r_count; i++) {
> + char flag = TTY_NORMAL;
>
> - /* TODO: handle sysrq */
> - tty_insert_flip_string(tport, buf, min(count, 4));
> - count -= 4;
> + if (msm_port->break_detected && buf[i] == 0) {
> + port->icount.brk++;
> + flag = TTY_BREAK;
> + msm_port->break_detected = false;
> + if (uart_handle_break(port))
> + continue;
> + }
> +
> + if (!(port->read_status_mask & UART_SR_RX_BREAK))
> + flag = TTY_NORMAL;
flag is already known to be TTY_NORMAL.
> +
> + spin_unlock(&port->lock);
Is it safe to unlock at this point? count may no longer be valid when we
return.
> + sysrq = uart_handle_sysrq_char(port, buf[i]);
> + spin_lock(&port->lock);
> + if (!sysrq)
> + tty_insert_flip_char(tport, buf[i], flag);
flag has a constant value here.
> + }
> + count -= r_count;
> }
>
> spin_unlock(&port->lock);
> @@ -291,6 +307,11 @@ static irqreturn_t msm_irq(int irq, void *dev_id)
> misr = msm_read(port, UART_MISR);
> msm_write(port, 0, UART_IMR); /* disable interrupt */
>
> + if (misr & UART_IMR_RXBREAK_START) {
> + msm_port->break_detected = true;
> + msm_write(port, UART_CR_CMD_RESET_RXBREAK_START, UART_CR);
> + }
> +
> if (misr & (UART_IMR_RXLEV | UART_IMR_RXSTALE)) {
> if (msm_port->is_uartdm)
> handle_rx_dm(port, misr);
> @@ -496,7 +517,7 @@ static int msm_startup(struct uart_port *port)
>
> /* turn on RX and CTS interrupts */
> msm_port->imr = UART_IMR_RXLEV | UART_IMR_RXSTALE |
> - UART_IMR_CURRENT_CTS;
> + UART_IMR_CURRENT_CTS | UART_IMR_RXBREAK_START;
>
> if (msm_port->is_uartdm) {
> msm_write(port, 0xFFFFFF, UARTDM_DMRX);
> diff --git a/drivers/tty/serial/msm_serial.h b/drivers/tty/serial/msm_serial.h
> index 73d3abe71e79..3e1c7138d8cd 100644
> --- a/drivers/tty/serial/msm_serial.h
> +++ b/drivers/tty/serial/msm_serial.h
> @@ -65,6 +65,7 @@
> #define UART_CR_TX_ENABLE (1 << 2)
> #define UART_CR_RX_DISABLE (1 << 1)
> #define UART_CR_RX_ENABLE (1 << 0)
> +#define UART_CR_CMD_RESET_RXBREAK_START ((1 << 11) | (2 << 4))
>
> #define UART_IMR 0x0014
> #define UART_IMR_TXLEV (1 << 0)
> @@ -72,6 +73,7 @@
> #define UART_IMR_RXLEV (1 << 4)
> #define UART_IMR_DELTA_CTS (1 << 5)
> #define UART_IMR_CURRENT_CTS (1 << 6)
> +#define UART_IMR_RXBREAK_START (1 << 10)
>
> #define UART_IPR_RXSTALE_LAST 0x20
> #define UART_IPR_STALE_LSB 0x1F
>
--
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