On Thu, 13 Oct 2022, Matthias Schiffer wrote:
> We were occasionally seeing the "Errata i202: timedout" on an AM335x
> board when repeatedly opening and closing a UART connected to an active
> sender. As new input may arrive at any time, it is possible to miss the
> "RX FIFO empty" condition, forcing the loop to wait until it times out.
I can see this problem could occur and why your patch fixes it.
> Nothing in the i202 Advisory states that such a wait is even necessary;
> other FIFO clear functions like serial8250_clear_fifos() do not wait
> either. For this reason, it seems safe to remove the wait, fixing the
> mentioned issue.
Checking the commit that added this driver and the loop along with it,
there was no information why it would be needed there either.
Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@xxxxxxxxxxxxxxx>
Thanks.
--
i.
> Fixes: 61929cf0169d ("tty: serial: Add 8250-core based omap driver")
> Signed-off-by: Matthias Schiffer <matthias.schiffer@xxxxxxxxxxxxxxx>
> ---
> drivers/tty/serial/8250/8250_omap.c | 17 -----------------
> 1 file changed, 17 deletions(-)
>
> diff --git a/drivers/tty/serial/8250/8250_omap.c b/drivers/tty/serial/8250/8250_omap.c
> index 41b8c6b27136..484f791617af 100644
> --- a/drivers/tty/serial/8250/8250_omap.c
> +++ b/drivers/tty/serial/8250/8250_omap.c
> @@ -193,27 +193,10 @@ static void omap8250_set_mctrl(struct uart_port *port, unsigned int mctrl)
> static void omap_8250_mdr1_errataset(struct uart_8250_port *up,
> struct omap8250_priv *priv)
> {
> - u8 timeout = 255;
> -
> serial_out(up, UART_OMAP_MDR1, priv->mdr1);
> udelay(2);
> serial_out(up, UART_FCR, up->fcr | UART_FCR_CLEAR_XMIT |
> UART_FCR_CLEAR_RCVR);
> - /*
> - * Wait for FIFO to empty: when empty, RX_FIFO_E bit is 0 and
> - * TX_FIFO_E bit is 1.
> - */
> - while (UART_LSR_THRE != (serial_in(up, UART_LSR) &
> - (UART_LSR_THRE | UART_LSR_DR))) {
> - timeout--;
> - if (!timeout) {
> - /* Should *never* happen. we warn and carry on */
> - dev_crit(up->port.dev, "Errata i202: timedout %x\n",
> - serial_in(up, UART_LSR));
> - break;
> - }
> - udelay(1);
> - }
> }
>
> static void omap_8250_get_divisor(struct uart_port *port, unsigned int baud,
>
