From: Anssi Hannula Date: Fri, 15 Feb 2019 16:45:08 +0000 (+0200) Subject: serial: uartps: Fix stuck ISR if RX disabled with non-empty FIFO X-Git-Tag: v5.1-rc1~143^2~9 X-Git-Url: https://asedeno.scripts.mit.edu/gitweb/?a=commitdiff_plain;h=7abab1605139bc41442864c18f9573440f7ca105;p=linux.git serial: uartps: Fix stuck ISR if RX disabled with non-empty FIFO 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 Cc: stable@vger.kernel.org Signed-off-by: Greg Kroah-Hartman --- 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);