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SubjectRe: [PATCH 03/10] tty: xuartps: Implement BREAK detection, add SYSRQ support
On 10/17/2013 05:08 PM, Soren Brinkmann wrote:
> From: Vlad Lungu <vlad.lungu@windriver.com>
>
> The Cadence UART does not do break detection, even if the
> datasheet says it does. This patch adds break detection in
> software (tested in 8N1 mode only) and enables SYSRQ,
> allowing for Break-g to enter KDB and all the other goodies.
>
> Signed-off-by: Vlad Lungu <vlad.lungu@windriver.com>
> Signed-off-by: Soren Brinkmann <soren.brinkmann@xilinx.com>
> ---
> I ported this patch to 3.12 and fixed some style issues
> ---
> drivers/tty/serial/xilinx_uartps.c | 50 +++++++++++++++++++++++++++++++++++++-
> 1 file changed, 49 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/tty/serial/xilinx_uartps.c b/drivers/tty/serial/xilinx_uartps.c
> index 8c0745951605..5d5557af4d22 100644
> --- a/drivers/tty/serial/xilinx_uartps.c
> +++ b/drivers/tty/serial/xilinx_uartps.c
> @@ -11,13 +11,17 @@
> *
> */
>
> +#if defined(CONFIG_SERIAL_XILINX_PS_UART_CONSOLE) && defined(CONFIG_MAGIC_SYSRQ)
> +#define SUPPORT_SYSRQ
> +#endif
> +
> #include <linux/platform_device.h>
> #include <linux/serial.h>
> +#include <linux/console.h>
> #include <linux/serial_core.h>
> #include <linux/slab.h>
> #include <linux/tty.h>
> #include <linux/tty_flip.h>
> -#include <linux/console.h>
> #include <linux/clk.h>
> #include <linux/irq.h>
> #include <linux/io.h>
> @@ -128,6 +132,9 @@
> #define XUARTPS_IXR_RXEMPTY 0x00000002 /* RX FIFO empty interrupt. */
> #define XUARTPS_IXR_MASK 0x00001FFF /* Valid bit mask */
>
> +/* Goes in read_status_mask for break detection as the HW doesn't do it*/
> +#define XUARTPS_IXR_BRK 0x80000000
> +
> /** Channel Status Register
> *
> * The channel status register (CSR) is provided to enable the control logic
> @@ -171,6 +178,23 @@ static irqreturn_t xuartps_isr(int irq, void *dev_id)
> */
> isrstatus = xuartps_readl(XUARTPS_ISR_OFFSET);
>
> + /*
> + * There is no hardware break detection, so we interpret framing
> + * error with all-zeros data as a break sequence. Most of the time,
> + * there's another non-zero byte at the end of the sequence.
> + */
> +
> + if (isrstatus & XUARTPS_IXR_FRAMING) {
> + while (!(xuartps_readl(XUARTPS_SR_OFFSET) &
> + XUARTPS_SR_RXEMPTY)) {
> + if (!xuartps_readl(XUARTPS_FIFO_OFFSET)) {
> + port->read_status_mask |= XUARTPS_IXR_BRK;
> + isrstatus &= ~XUARTPS_IXR_FRAMING;
> + }
> + }
> + xuartps_writel(XUARTPS_IXR_FRAMING, XUARTPS_ISR_OFFSET);
> + }
> +
> /* drop byte with parity error if IGNPAR specified */
> if (isrstatus & port->ignore_status_mask & XUARTPS_IXR_PARITY)
> isrstatus &= ~(XUARTPS_IXR_RXTRIG | XUARTPS_IXR_TOUT);
> @@ -184,6 +208,30 @@ static irqreturn_t xuartps_isr(int irq, void *dev_id)
> while ((xuartps_readl(XUARTPS_SR_OFFSET) &
> XUARTPS_SR_RXEMPTY) != XUARTPS_SR_RXEMPTY) {
> data = xuartps_readl(XUARTPS_FIFO_OFFSET);
> +
> + /* Non-NULL byte after BREAK is garbage (99%) */
> + if (data && (port->read_status_mask &
> + XUARTPS_IXR_BRK)) {
> + port->read_status_mask &= ~XUARTPS_IXR_BRK;
> + port->icount.brk++;
> + if (uart_handle_break(port))
> + continue;
> + }
> +
> + /*
> + * uart_handle_sysrq_char() doesn't work if
> + * spinlocked, for some reason
> + */
^^^^^^^^^^^^^^^
Because the console write method, xuartps_console_write(), tries to
lock the port->lock. Double-claim deadlock.

> + if (port->sysrq) {
> + spin_unlock(&port->lock);
> + if (uart_handle_sysrq_char(port,
> + (unsigned char)data)) {
> + spin_lock(&port->lock);
> + continue;
> + }
> + spin_lock(&port->lock);
> + }
> +
> port->icount.rx++;
>
> if (isrstatus & XUARTPS_IXR_PARITY) {
>



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