This is a note to let you know that I've just added the patch titled serial: 8250: 8250_omap: Fix possible interrupt storm on K3 SoCs to the 5.13-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: serial-8250-8250_omap-fix-possible-interrupt-storm-o.patch and it can be found in the queue-5.13 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. commit dfc0277bd5e79ea6eefdaaf9994d6f6e408718ea Author: Vignesh Raghavendra <vigneshr@xxxxxx> Date: Tue Jun 22 20:27:04 2021 +0530 serial: 8250: 8250_omap: Fix possible interrupt storm on K3 SoCs [ 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@xxxxxxxxxxx> Tested-by: Jan Kiszka <jan.kiszka@xxxxxxxxxxx> Signed-off-by: Vignesh Raghavendra <vigneshr@xxxxxx> Link: https://lore.kernel.org/r/20210622145704.11168-1-vigneshr@xxxxxx Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx> diff --git a/drivers/tty/serial/8250/8250_omap.c b/drivers/tty/serial/8250/8250_omap.c index c06631ced414..79418d4beb48 100644 --- 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 = {