On Tue, 14 Nov 2023 08:49:04 +0100 Daniel Mack <daniel@xxxxxxxxxx> wrote: Hi, > This devices has a silicon bug that makes it report a timeout interrupt > but no data in FIFO. > > The datasheet states the following in the errata section 18.1.4: > > "If the host reads the receive FIFO at the at the same time as a > time-out interrupt condition happens, the host might read 0xCC > (time-out) in the Interrupt Indication Register (IIR), but bit 0 > of the Line Status Register (LSR) is not set (means there is not > data in the receive FIFO)." > > When this happens, the loop in sc16is7xx_irq() will run forever, > which effectively blocks the i2c bus and breaks the functionality > of the UART. > > From the information above, it is assumed that when the bug is > triggered, the FIFO does in fact have payload in its buffer, but the > fill level reporting is off-by-one. Hence this patch fixes the issue > by reading one byte from the FIFO when that condition is detected. >From what I understand from the errata, when the problem occurs, it affects bit 0 of the LSR register. I see no mention that it also affects the RX FIFO level register (SC16IS7XX_RXLVL_REG)? LSR[0] would be checked only if we were using polled mode of operation, but we always use the interrupt mode (IRQ), and therefore I would say that this errata doesn't apply to this driver, and the patch is not necessary... Hugo. > This clears the interrupt and hence breaks the polling loop. > > Signed-off-by: Daniel Mack <daniel@xxxxxxxxxx> > Co-Developed-by: Maxim Popov <maxim.snafu@xxxxxxxxx> > Cc: stable@xxxxxxxxxxxxxxx > --- > drivers/tty/serial/sc16is7xx.c | 12 ++++++++++++ > 1 file changed, 12 insertions(+) > > diff --git a/drivers/tty/serial/sc16is7xx.c b/drivers/tty/serial/sc16is7xx.c > index 289ca7d4e566..76f76e510ed1 100644 > --- a/drivers/tty/serial/sc16is7xx.c > +++ b/drivers/tty/serial/sc16is7xx.c > @@ -765,6 +765,18 @@ static bool sc16is7xx_port_irq(struct sc16is7xx_port *s, int portno) > case SC16IS7XX_IIR_RTOI_SRC: > case SC16IS7XX_IIR_XOFFI_SRC: > rxlen = sc16is7xx_port_read(port, SC16IS7XX_RXLVL_REG); > + > + /* > + * There is a silicon bug that makes the chip report a > + * time-out interrupt but no data in the FIFO. This is > + * described in errata section 18.1.4. > + * > + * When this happens, read one byte from the FIFO to > + * clear the interrupt. > + */ > + if (iir == SC16IS7XX_IIR_RTOI_SRC && !rxlen) > + rxlen = 1; > + > if (rxlen) > sc16is7xx_handle_rx(port, rxlen, iir); > break; > -- > 2.41.0 >
