On 22.06.21 16:57, Vignesh Raghavendra wrote:
> 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>
> Signed-off-by: Vignesh Raghavendra <vigneshr@xxxxxx>
> ---
> v2:
> Restrict workaround to K3 family of devices only (ti,am654-uart) where
> issue was reported.
>
> v1: https://lore.kernel.org/r/20210511151955.28071-1-vigneshr@xxxxxx
>
> drivers/tty/serial/8250/8250_omap.c | 20 +++++++++++++++++++-
> 1 file changed, 19 insertions(+), 1 deletion(-)
>
> 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 = {
>
Tested-by: Jan Kiszka <jan.kiszka@xxxxxxxxxxx>
Thanks,
Jan
--
Siemens AG, T RDA IOT
Corporate Competence Center Embedded Linux
