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serial: 8250_dw: Avoid pslverr on reading empty receiver fifo

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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 <andriy.shevchenko@linux.intel.com>
Signed-off-by: VAMSHI GAJJELA <vamshigajjela@google.com>
Link: https://lore.kernel.org/r/20220713131722.2316829-1-vamshigajjela@google.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
VAMSHI GAJJELA 2022-07-13 18:47:22 +05:30 committed by Greg Kroah-Hartman
parent 1d46c08d24
commit 4f4e670342
1 changed files with 13 additions and 0 deletions
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13
drivers/tty/serial/8250/8250_dw.c
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@ -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);
}