DW UART sometimes triggers IIR_RDI during DMA Rx when IIR_RX_TIMEOUT should have been triggered instead. Since IIR_RDI has higher priority than IIR_RX_TIMEOUT, this causes the Rx to hang into interrupt loop. The problem seems to occur at least with some combinations of small-sized transfers (I've reproduced the problem on Elkhart Lake PSE UARTs).

If there's already an on-going Rx DMA and IIR_RDI triggers, fall graciously back to non-DMA Rx. That is, behave as if IIR_RX_TIMEOUT had occurred.

8250_omap already considers IIR_RDI similar to this change so its nothing unheard of.

Fixes: 75df022b5f89 ("serial: 8250_dma: Fix RX handling") Cc: stable@vger.kernel.org Co-developed-by: Srikanth Thokala srikanth.thokala@intel.com Signed-off-by: Srikanth Thokala srikanth.thokala@intel.com Co-developed-by: Aman Kumar aman.kumar@intel.com Signed-off-by: Aman Kumar aman.kumar@intel.com Signed-off-by: Ilpo Järvinen ilpo.jarvinen@linux.intel.com --- drivers/tty/serial/8250/8250_port.c | 4 ++++ 1 file changed, 4 insertions(+)

diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c index fe8662cd9402..92dd18716169 100644 --- a/drivers/tty/serial/8250/8250_port.c +++ b/drivers/tty/serial/8250/8250_port.c @@ -1897,6 +1897,10 @@ EXPORT_SYMBOL_GPL(serial8250_modem_status); static bool handle_rx_dma(struct uart_8250_port *up, unsigned int iir) { switch (iir & 0x3f) { + case UART_IIR_RDI: + if (!up->dma->rx_running) + break; + fallthrough; case UART_IIR_RX_TIMEOUT: serial8250_rx_dma_flush(up); fallthrough;