serial: 8250: 8250_omap: Fix possible interrupt storm on K3 SoCs

BugLink: https://bugs.launchpad.net/bugs/1938340
[ Upstream commit b67e830d38fa9335d927fe67e812e3ed81b4689c ]

On K3 family of SoCs (which includes AM654 SoC), it is observed that RX
TIMEOUT is signalled after RX FIFO has been drained, in which case a
dummy read of RX FIFO is required to clear RX TIMEOUT condition.
Otherwise, this would lead to an interrupt storm.

Fix this by introducing UART_RX_TIMEOUT_QUIRK flag and doing a dummy
read in IRQ handler when RX TIMEOUT is reported with no data in RX FIFO.

Fixes: be70874498f3 ("serial: 8250_omap: Add support for AM654 UART controller")
Reported-by: Jan Kiszka <jan.kiszka@siemens.com>
Tested-by: Jan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: Vignesh Raghavendra <vigneshr@ti.com>
Link: https://lore.kernel.org/r/20210622145704.11168-1-vigneshr@ti.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>

diff --git a/drivers/tty/serial/8250/8250_omap.c b/drivers/tty/serial/8250/8250_omap.c
index 3161d36556706b949a3cb0952b8af2513988d9b4..c37468887fd2a554da105feb78ce54a7523c1a02 100644 (file)
--- a/drivers/tty/serial/8250/8250_omap.c
+++ b/drivers/tty/serial/8250/8250_omap.c
@@ -43,6 +43,7 @@
 #define UART_ERRATA_CLOCK_DISABLE      (1 << 3)
 #define        UART_HAS_EFR2                   BIT(4)
 #define UART_HAS_RHR_IT_DIS            BIT(5)
+#define UART_RX_TIMEOUT_QUIRK          BIT(6)
 
 #define OMAP_UART_FCR_RX_TRIG          6
 #define OMAP_UART_FCR_TX_TRIG          4
@@ -104,6 +105,9 @@
 #define UART_OMAP_EFR2                 0x23
 #define UART_OMAP_EFR2_TIMEOUT_BEHAVE  BIT(6)
 
+/* RX FIFO occupancy indicator */
+#define UART_OMAP_RX_LVL               0x64
+
 struct omap8250_priv {
        int line;
        u8 habit;
@@ -611,6 +615,7 @@ static int omap_8250_dma_handle_irq(struct uart_port *port);
 static irqreturn_t omap8250_irq(int irq, void *dev_id)
 {
        struct uart_port *port = dev_id;
+       struct omap8250_priv *priv = port->private_data;
        struct uart_8250_port *up = up_to_u8250p(port);
        unsigned int iir;
        int ret;
@@ -625,6 +630,18 @@ static irqreturn_t omap8250_irq(int irq, void *dev_id)
        serial8250_rpm_get(up);
        iir = serial_port_in(port, UART_IIR);
        ret = serial8250_handle_irq(port, iir);
+
+       /*
+        * 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.
+        */
+       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);
+       }
+
        serial8250_rpm_put(up);
 
        return IRQ_RETVAL(ret);
@@ -1218,7 +1235,8 @@ static struct omap8250_dma_params am33xx_dma = {
 
 static struct omap8250_platdata am654_platdata = {
        .dma_params     = &am654_dma,
-       .habit          = UART_HAS_EFR2 | UART_HAS_RHR_IT_DIS,
+       .habit          = UART_HAS_EFR2 | UART_HAS_RHR_IT_DIS |
+                         UART_RX_TIMEOUT_QUIRK,
 };
 
 static struct omap8250_platdata am33xx_platdata = {