If RX is disabled while there are still unprocessed bytes in RX FIFO, cdns_uart_handle_rx() called from interrupt handler will get stuck in the receive loop as read bytes will not get removed from the RX FIFO and CDNS_UART_SR_RXEMPTY bit will never get set.
Avoid the stuck handler by checking first if RX is disabled. port->lock protects against race with RX-disabling functions.
This HW behavior was mentioned by Nathan Rossi in 43e98facc4a3 ("tty: xuartps: Fix RX hang, and TX corruption in termios call") which fixed a similar issue in cdns_uart_set_termios(). The behavior can also be easily verified by e.g. setting CDNS_UART_CR_RX_DIS at the beginning of cdns_uart_handle_rx() - the following loop will then get stuck.
Resetting the FIFO using RXRST would not set RXEMPTY either so simply issuing a reset after RX-disable would not work.
I observe this frequently on a ZynqMP board during heavy RX load at 1M baudrate when the reader process exits and thus RX gets disabled.
Fixes: 61ec9016988f ("tty/serial: add support for Xilinx PS UART") Signed-off-by: Anssi Hannula anssi.hannula@bitwise.fi Cc: stable@vger.kernel.org --- drivers/tty/serial/xilinx_uartps.c | 7 +++++++ 1 file changed, 7 insertions(+)
diff --git a/drivers/tty/serial/xilinx_uartps.c b/drivers/tty/serial/xilinx_uartps.c index 094f2958cb2b..f0c4f59d9314 100644 --- a/drivers/tty/serial/xilinx_uartps.c +++ b/drivers/tty/serial/xilinx_uartps.c @@ -219,6 +219,13 @@ static void cdns_uart_handle_rx(void *dev_id, unsigned int isrstatus)
is_rxbs_support = cdns_uart->quirks & CDNS_UART_RXBS_SUPPORT;
+ /* + * RXEMPTY will never be set if RX is disabled as read bytes + * will not be removed from the FIFO + */ + if (readl(port->membase + CDNS_UART_CR) & CDNS_UART_CR_RX_DIS) + return; + while ((readl(port->membase + CDNS_UART_SR) & CDNS_UART_SR_RXEMPTY) != CDNS_UART_SR_RXEMPTY) { if (is_rxbs_support)
+ Shubhrajyoti
On 06. 02. 19 15:08, Anssi Hannula wrote:
If RX is disabled while there are still unprocessed bytes in RX FIFO, cdns_uart_handle_rx() called from interrupt handler will get stuck in the receive loop as read bytes will not get removed from the RX FIFO and CDNS_UART_SR_RXEMPTY bit will never get set.
Avoid the stuck handler by checking first if RX is disabled. port->lock protects against race with RX-disabling functions.
This HW behavior was mentioned by Nathan Rossi in 43e98facc4a3 ("tty: xuartps: Fix RX hang, and TX corruption in termios call") which fixed a similar issue in cdns_uart_set_termios(). The behavior can also be easily verified by e.g. setting CDNS_UART_CR_RX_DIS at the beginning of cdns_uart_handle_rx() - the following loop will then get stuck.
Resetting the FIFO using RXRST would not set RXEMPTY either so simply issuing a reset after RX-disable would not work.
I observe this frequently on a ZynqMP board during heavy RX load at 1M baudrate when the reader process exits and thus RX gets disabled.
Fixes: 61ec9016988f ("tty/serial: add support for Xilinx PS UART") Signed-off-by: Anssi Hannula anssi.hannula@bitwise.fi Cc: stable@vger.kernel.org
drivers/tty/serial/xilinx_uartps.c | 7 +++++++ 1 file changed, 7 insertions(+)
diff --git a/drivers/tty/serial/xilinx_uartps.c b/drivers/tty/serial/xilinx_uartps.c index 094f2958cb2b..f0c4f59d9314 100644 --- a/drivers/tty/serial/xilinx_uartps.c +++ b/drivers/tty/serial/xilinx_uartps.c @@ -219,6 +219,13 @@ static void cdns_uart_handle_rx(void *dev_id, unsigned int isrstatus) is_rxbs_support = cdns_uart->quirks & CDNS_UART_RXBS_SUPPORT;
- /*
* RXEMPTY will never be set if RX is disabled as read bytes* will not be removed from the FIFO*/- if (readl(port->membase + CDNS_UART_CR) & CDNS_UART_CR_RX_DIS)
return;- while ((readl(port->membase + CDNS_UART_SR) & CDNS_UART_SR_RXEMPTY) != CDNS_UART_SR_RXEMPTY) { if (is_rxbs_support)
Please review. M
Hi Anssi,
Thanks for the patch.
Minor nit below. The call to the cdns_uart_handle_rx could be prevented in cdns_uart_isr
-----Original Message----- From: Michal Simek [mailto:michal.simek@xilinx.com] Sent: Thursday, February 14, 2019 12:06 PM To: Anssi Hannula anssi.hannula@bitwise.fi; Michal Simek michals@xilinx.com; Greg Kroah-Hartman gregkh@linuxfoundation.org Cc: Jiri Slaby jslaby@suse.com; linux-serial@vger.kernel.org; linux-arm- kernel@lists.infradead.org; stable@vger.kernel.org; Shubhrajyoti Datta shubhraj@xilinx.com Subject: Re: [PATCH] serial: uartps: Fix stuck ISR if RX disabled with non- empty FIFO
- Shubhrajyoti
On 06. 02. 19 15:08, Anssi Hannula wrote:
If RX is disabled while there are still unprocessed bytes in RX FIFO, cdns_uart_handle_rx() called from interrupt handler will get stuck in the receive loop as read bytes will not get removed from the RX FIFO and CDNS_UART_SR_RXEMPTY bit will never get set.
Avoid the stuck handler by checking first if RX is disabled. port->lock protects against race with RX-disabling functions.
This HW behavior was mentioned by Nathan Rossi in 43e98facc4a3 ("tty: xuartps: Fix RX hang, and TX corruption in termios call") which fixed a similar issue in cdns_uart_set_termios(). The behavior can also be easily verified by e.g. setting CDNS_UART_CR_RX_DIS at the beginning of cdns_uart_handle_rx() - the following loop will then get stuck.
Resetting the FIFO using RXRST would not set RXEMPTY either so simply issuing a reset after RX-disable would not work.
I observe this frequently on a ZynqMP board during heavy RX load at 1M baudrate when the reader process exits and thus RX gets disabled.
Reviewed-by: Shubhrajyoti Datta shubhrajyori.datta@xilinx.com
Fixes: 61ec9016988f ("tty/serial: add support for Xilinx PS UART") Signed-off-by: Anssi Hannula anssi.hannula@bitwise.fi Cc: stable@vger.kernel.org
drivers/tty/serial/xilinx_uartps.c | 7 +++++++ 1 file changed, 7 insertions(+)
diff --git a/drivers/tty/serial/xilinx_uartps.c b/drivers/tty/serial/xilinx_uartps.c index 094f2958cb2b..f0c4f59d9314 100644 --- a/drivers/tty/serial/xilinx_uartps.c +++ b/drivers/tty/serial/xilinx_uartps.c @@ -219,6 +219,13 @@ static void cdns_uart_handle_rx(void *dev_id, unsigned int isrstatus)
is_rxbs_support = cdns_uart->quirks & CDNS_UART_RXBS_SUPPORT;
- /*
* RXEMPTY will never be set if RX is disabled as read bytes* will not be removed from the FIFO*/- if (readl(port->membase + CDNS_UART_CR) &
CDNS_UART_CR_RX_DIS)
return;- while ((readl(port->membase + CDNS_UART_SR) & CDNS_UART_SR_RXEMPTY) != CDNS_UART_SR_RXEMPTY) { if (is_rxbs_support)
Please review. M
If RX is disabled while there are still unprocessed bytes in RX FIFO, cdns_uart_handle_rx() called from interrupt handler will get stuck in the receive loop as read bytes will not get removed from the RX FIFO and CDNS_UART_SR_RXEMPTY bit will never get set.
Avoid the stuck handler by checking first if RX is disabled. port->lock protects against race with RX-disabling functions.
This HW behavior was mentioned by Nathan Rossi in 43e98facc4a3 ("tty: xuartps: Fix RX hang, and TX corruption in termios call") which fixed a similar issue in cdns_uart_set_termios(). The behavior can also be easily verified by e.g. setting CDNS_UART_CR_RX_DIS at the beginning of cdns_uart_handle_rx() - the following loop will then get stuck.
Resetting the FIFO using RXRST would not set RXEMPTY either so simply issuing a reset after RX-disable would not work.
I observe this frequently on a ZynqMP board during heavy RX load at 1M baudrate when the reader process exits and thus RX gets disabled.
Fixes: 61ec9016988f ("tty/serial: add support for Xilinx PS UART") Signed-off-by: Anssi Hannula anssi.hannula@bitwise.fi Cc: stable@vger.kernel.org ---
Shubhrajyoti Datta wrote:
Minor nit below. The call to the cdns_uart_handle_rx could be prevented in cdns_uart_isr
OK, changed, thanks.
Personally I liked it slightly better in handle_rx() closer to the problematic loop (and RX being disabled here should be rare), but I'm fine with either.
v2: Moved check from cdns_uart_handle_rx() to caller.
drivers/tty/serial/xilinx_uartps.c | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-)
diff --git a/drivers/tty/serial/xilinx_uartps.c b/drivers/tty/serial/xilinx_uartps.c index 094f2958cb2b..ee9f18c52d29 100644 --- a/drivers/tty/serial/xilinx_uartps.c +++ b/drivers/tty/serial/xilinx_uartps.c @@ -364,7 +364,13 @@ static irqreturn_t cdns_uart_isr(int irq, void *dev_id) cdns_uart_handle_tx(dev_id); isrstatus &= ~CDNS_UART_IXR_TXEMPTY; } - if (isrstatus & CDNS_UART_IXR_RXMASK) + + /* + * Skip RX processing if RX is disabled as RXEMPTY will never be set + * as read bytes will not be removed from the FIFO. + */ + if (isrstatus & CDNS_UART_IXR_RXMASK && + !(readl(port->membase + CDNS_UART_CR) & CDNS_UART_CR_RX_DIS)) cdns_uart_handle_rx(dev_id, isrstatus);
spin_unlock(&port->lock);
linux-stable-mirror@lists.linaro.org
-
Anssi Hannula -
Michal Simek -
Shubhrajyoti Datta