releases/4.19.31/serial-uartps-fix-stuck-isr-if-rx-disabled-with-non-empty-fifo.patch

   1 From 7abab1605139bc41442864c18f9573440f7ca105 Mon Sep 17 00:00:00 2001
   2 From: Anssi Hannula <anssi.hannula@bitwise.fi>
   3 Date: Fri, 15 Feb 2019 18:45:08 +0200
   4 Subject: serial: uartps: Fix stuck ISR if RX disabled with non-empty FIFO
   5
   6 From: Anssi Hannula <anssi.hannula@bitwise.fi>
   7
   8 commit 7abab1605139bc41442864c18f9573440f7ca105 upstream.
   9
  10 If RX is disabled while there are still unprocessed bytes in RX FIFO,
  11 cdns_uart_handle_rx() called from interrupt handler will get stuck in
  12 the receive loop as read bytes will not get removed from the RX FIFO
  13 and CDNS_UART_SR_RXEMPTY bit will never get set.
  14
  15 Avoid the stuck handler by checking first if RX is disabled. port->lock
  16 protects against race with RX-disabling functions.
  17
  18 This HW behavior was mentioned by Nathan Rossi in 43e98facc4a3 ("tty:
  19 xuartps: Fix RX hang, and TX corruption in termios call") which fixed a
  20 similar issue in cdns_uart_set_termios().
  21 The behavior can also be easily verified by e.g. setting
  22 CDNS_UART_CR_RX_DIS at the beginning of cdns_uart_handle_rx() - the
  23 following loop will then get stuck.
  24
  25 Resetting the FIFO using RXRST would not set RXEMPTY either so simply
  26 issuing a reset after RX-disable would not work.
  27
  28 I observe this frequently on a ZynqMP board during heavy RX load at 1M
  29 baudrate when the reader process exits and thus RX gets disabled.
  30
  31 Fixes: 61ec9016988f ("tty/serial: add support for Xilinx PS UART")
  32 Signed-off-by: Anssi Hannula <anssi.hannula@bitwise.fi>
  33 Cc: stable@vger.kernel.org
  34 Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
  35
  36 ---
  37  drivers/tty/serial/xilinx_uartps.c |    8 +++++++-
  38  1 file changed, 7 insertions(+), 1 deletion(-)
  39
  40 --- a/drivers/tty/serial/xilinx_uartps.c
  41 +++ b/drivers/tty/serial/xilinx_uartps.c
  42 @@ -362,7 +362,13 @@ static irqreturn_t cdns_uart_isr(int irq
  43                 cdns_uart_handle_tx(dev_id);
  44                 isrstatus &= ~CDNS_UART_IXR_TXEMPTY;
  45         }
  46 -       if (isrstatus & CDNS_UART_IXR_RXMASK)
  47 +
  48 +       /*
  49 +        * Skip RX processing if RX is disabled as RXEMPTY will never be set
  50 +        * as read bytes will not be removed from the FIFO.
  51 +        */
  52 +       if (isrstatus & CDNS_UART_IXR_RXMASK &&
  53 +           !(readl(port->membase + CDNS_UART_CR) & CDNS_UART_CR_RX_DIS))
  54                 cdns_uart_handle_rx(dev_id, isrstatus);
  55
  56         spin_unlock(&port->lock);