From 4f4e670342b14f302e17c93bd22fc943bbaaf1de Mon Sep 17 00:00:00 2001 From: VAMSHI GAJJELA Date: Wed, 13 Jul 2022 18:47:22 +0530 Subject: [PATCH] serial: 8250_dw: Avoid pslverr on reading empty receiver fifo With PSLVERR_RESP_EN parameter set to 1, the device generates an error response when an attempt to read an empty RBR with FIFO enabled. This happens when LCR writes are ignored when UART is busy. dw8250_check_lcr() in retries to update LCR, invokes dw8250_force_idle() to clear and reset FIFO and eventually reads UART_RX causing the error. Avoid this by not reading RBR/UART_RX when no data is available. Reviewed-by: Andy Shevchenko Signed-off-by: VAMSHI GAJJELA Link: https://lore.kernel.org/r/20220713131722.2316829-1-vamshigajjela@google.com Signed-off-by: Greg Kroah-Hartman --- drivers/tty/serial/8250/8250_dw.c | 13 +++++++++++++ 1 file changed, 13 insertions(+) diff --git a/drivers/tty/serial/8250/8250_dw.c b/drivers/tty/serial/8250/8250_dw.c index e419e03..f9e85ed 100644 --- a/drivers/tty/serial/8250/8250_dw.c +++ b/drivers/tty/serial/8250/8250_dw.c @@ -83,8 +83,21 @@ static inline int dw8250_modify_msr(struct uart_port *p, int offset, int value) static void dw8250_force_idle(struct uart_port *p) { struct uart_8250_port *up = up_to_u8250p(p); + unsigned int lsr; serial8250_clear_and_reinit_fifos(up); + + /* + * With PSLVERR_RESP_EN parameter set to 1, the device generates an + * error response when an attempt to read an empty RBR with FIFO + * enabled. + */ + if (up->fcr & UART_FCR_ENABLE_FIFO) { + lsr = p->serial_in(p, UART_LSR); + if (!(lsr & UART_LSR_DR)) + return; + } + (void)p->serial_in(p, UART_RX); } -- 2.7.4