diff options
Diffstat (limited to 'drivers/tty/serial/8250/8250_fsl.c')
| -rw-r--r-- | drivers/tty/serial/8250/8250_fsl.c | 14 |
1 files changed, 13 insertions, 1 deletions
diff --git a/drivers/tty/serial/8250/8250_fsl.c b/drivers/tty/serial/8250/8250_fsl.c index 8adfaa183f77..00f46b9a8b09 100644 --- a/drivers/tty/serial/8250/8250_fsl.c +++ b/drivers/tty/serial/8250/8250_fsl.c @@ -38,7 +38,19 @@ int fsl8250_handle_irq(struct uart_port *port) return 0; } - /* This is the WAR; if last event was BRK, then read and return */ + /* + * For a single break the hardware reports LSR.BI for each character + * time. This is described in the MPC8313E chip errata as "General17". + * A typical break has a duration of 0.3s, with a 115200n8 configuration + * that (theoretically) corresponds to ~3500 interrupts in these 0.3s. + * In practise it's less (around 500) because of hardware + * and software latencies. The workaround recommended by the vendor is + * to read the RX register (to clear LSR.DR and thus prevent a FIFO + * aging interrupt). To prevent the irq from retriggering LSR must not be + * read. (This would clear LSR.BI, hardware would reassert the BI event + * immediately and interrupt the CPU again. The hardware clears LSR.BI + * when the next valid char is read.) + */ if (unlikely(up->lsr_saved_flags & UART_LSR_BI)) { up->lsr_saved_flags &= ~UART_LSR_BI; port->serial_in(port, UART_RX); |