Commit 4f4e6703 authored by VAMSHI GAJJELA's avatar VAMSHI GAJJELA Committed by Greg Kroah-Hartman
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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: default avatarAndy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: default avatarVAMSHI GAJJELA <vamshigajjela@google.com>
Link: https://lore.kernel.org/r/20220713131722.2316829-1-vamshigajjela@google.com


Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 1d46c08d

drivers/tty/serial/8250/8250_dw.c

+13 −0
Original line number Diff line number Diff line
@@ -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);

}