[PATCH v2] serial: 8250_omap: Fix Errata i2310 with RX FIFO level check

[Udit Kumar <u-kumar1@ti.com>]

Errata i2310[0] says, Erroneous timeout can be triggered,
if this Erroneous interrupt is not cleared then it may leads
to storm of interrupts.

Commit 9d141c1e6157 ("serial: 8250_omap: Implementation of Errata i2310")
which added the workaround but missed ensuring RX FIFO is really empty
before applying the errata workaround as recommended in the errata text.
Fix this by adding back check for UART_OMAP_RX_LVL to be 0 for
workaround to take effect.

[0] https://www.ti.com/lit/pdf/sprz536 page 23

Fixes: 9d141c1e6157 ("serial: 8250_omap: Implementation of Errata i2310")
Cc: stable@vger.kernel.org
Reported-by: Vignesh Raghavendra <vigneshr@ti.com>
Closes: https://lore.kernel.org/all/e96d0c55-0b12-4cbf-9d23-48963543de49@ti.com/
Signed-off-by: Udit Kumar <u-kumar1@ti.com>
---
Testlogs
https://gist.github.com/uditkumarti/4f5120f203a238fbebe411eb82b63753

Changelog:
Changes in v2
- Update commit message, subject, Fixes tag
link to v1:
https://lore.kernel.org/all/20240625051338.2761599-1-u-kumar1@ti.com/

 drivers/tty/serial/8250/8250_omap.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/tty/serial/8250/8250_omap.c b/drivers/tty/serial/8250/8250_omap.c
index ddac0a13cf84..1af9aed99c65 100644
--- a/drivers/tty/serial/8250/8250_omap.c
+++ b/drivers/tty/serial/8250/8250_omap.c
@@ -672,7 +672,8 @@ static irqreturn_t omap8250_irq(int irq, void *dev_id)
 	 * https://www.ti.com/lit/pdf/sprz536
 	 */
 	if (priv->habit & UART_RX_TIMEOUT_QUIRK &&
-		(iir & UART_IIR_RX_TIMEOUT) == UART_IIR_RX_TIMEOUT) {
+	    (iir & UART_IIR_RX_TIMEOUT) == UART_IIR_RX_TIMEOUT &&
+	    serial_port_in(port, UART_OMAP_RX_LVL) == 0) {
 		unsigned char efr2, timeout_h, timeout_l;
 
 		efr2 = serial_in(up, UART_OMAP_EFR2);
-- 
2.34.1