linux-kernel - [PATCH v2] serial: 8250_omap: Implementation of Errata i2310

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Message-ID: <20240617052253.2188140-1-u-kumar1@ti.com>
Date: Mon, 17 Jun 2024 10:52:53 +0530
From: Udit Kumar <u-kumar1@...com>
To: <vigneshr@...com>, <nm@...com>, <tony@...mide.com>
CC: <gregkh@...uxfoundation.org>, <jirislaby@...nel.org>,
        <u.kleine-koenig@...gutronix.de>, <ronald.wahl@...itan.com>,
        <thomas.richard@...tlin.com>, <tglx@...utronix.de>,
        <linux-kernel@...r.kernel.org>, <linux-serial@...r.kernel.org>,
        <ilpo.jarvinen@...ux.intel.com>, Udit Kumar <u-kumar1@...com>
Subject: [PATCH v2] serial: 8250_omap: Implementation of Errata i2310

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

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

Fixes: b67e830d38fa ("serial: 8250: 8250_omap: Fix possible interrupt storm on K3 SoCs")
Signed-off-by: Udit Kumar <u-kumar1@...com>
---
Test logs
https://gist.github.com/uditkumarti/7a7ab6994581bbb09cf1a4271c592d8e

Change logs
Changes in v2:
- Added Fixes Tag and typo correction in commit message
- Corrected bit position to UART_OMAP_EFR2_TIMEOUT_BEHAVE
Link to v1
https://lore.kernel.org/all/20240614061314.290840-1-u-kumar1@ti.com/

 drivers/tty/serial/8250/8250_omap.c | 25 ++++++++++++++++++++-----
 1 file changed, 20 insertions(+), 5 deletions(-)

diff --git a/drivers/tty/serial/8250/8250_omap.c b/drivers/tty/serial/8250/8250_omap.c
index 170639d12b2a..ddac0a13cf84 100644
--- a/drivers/tty/serial/8250/8250_omap.c
+++ b/drivers/tty/serial/8250/8250_omap.c
@@ -115,6 +115,10 @@
 /* RX FIFO occupancy indicator */
 #define UART_OMAP_RX_LVL		0x19
 
+/* Timeout low and High */
+#define UART_OMAP_TO_L                 0x26
+#define UART_OMAP_TO_H                 0x27
+
 /*
  * Copy of the genpd flags for the console.
  * Only used if console suspend is disabled
@@ -663,13 +667,24 @@ static irqreturn_t omap8250_irq(int irq, void *dev_id)
 
 	/*
 	 * On K3 SoCs, it is observed that RX TIMEOUT is signalled after
-	 * FIFO has been drained, in which case a dummy read of RX FIFO
-	 * is required to clear RX TIMEOUT condition.
+	 * FIFO has been drained or erroneously.
+	 * So apply solution of Errata i2310 as mentioned in
+	 * https://www.ti.com/lit/pdf/sprz536
 	 */
 	if (priv->habit & UART_RX_TIMEOUT_QUIRK &&
-	    (iir & UART_IIR_RX_TIMEOUT) == UART_IIR_RX_TIMEOUT &&
-	    serial_port_in(port, UART_OMAP_RX_LVL) == 0) {
-		serial_port_in(port, UART_RX);
+		(iir & UART_IIR_RX_TIMEOUT) == UART_IIR_RX_TIMEOUT) {
+		unsigned char efr2, timeout_h, timeout_l;
+
+		efr2 = serial_in(up, UART_OMAP_EFR2);
+		timeout_h = serial_in(up, UART_OMAP_TO_H);
+		timeout_l = serial_in(up, UART_OMAP_TO_L);
+		serial_out(up, UART_OMAP_TO_H, 0xFF);
+		serial_out(up, UART_OMAP_TO_L, 0xFF);
+		serial_out(up, UART_OMAP_EFR2, UART_OMAP_EFR2_TIMEOUT_BEHAVE);
+		serial_in(up, UART_IIR);
+		serial_out(up, UART_OMAP_EFR2, efr2);
+		serial_out(up, UART_OMAP_TO_H, timeout_h);
+		serial_out(up, UART_OMAP_TO_L, timeout_l);
 	}
 
 	/* Stop processing interrupts on input overrun */
-- 
2.34.1