On Wed, 22 Nov 2023 08:35:41 +0100 Daniel Mack <daniel@xxxxxxxxxx> wrote: > This device has a silicon bug that makes it report a timeout interrupt > but no data in the FIFO. > > The datasheet states the following in the errata section 18.1.4: > > "If the host reads the receive FIFO 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 no > data in the receive FIFO)." > > The errata doesn't explicitly mention that, but tests have shown > and the vendor has confirmed that the RXLVL register is equally > affected. Hi Daniel, thank you for the feedback from NXP. I would suggest to replace this paragraph with something like this: ------ The errata description seems to indicate it affects only polled mode of operation when reading bit 0 of the LSR register. But when using interrupt mode (IRQ) like this driver does, reading RXLVL gives a value of zero even if there is data in the Rx FIFO (confirmed by tests and NXP). ------ > This bug has hit us on production units and when it does, sc16is7xx_irq() > would spin forever because sc16is7xx_port_irq() keeps seeing an > interrupt in the IIR register that is not cleared because the driver > does not call into sc16is7xx_handle_rx() unless the RXLVL register > reports at least one byte in the FIFO. > > Fix this by always reading one byte when this condition is detected Change "reading one byte" to "reading one byte from the Rx FIFO". > in order to clear the interrupt. This approach was confirmed to be > correct by NXP through their support channels. > > Signed-off-by: Daniel Mack <daniel@xxxxxxxxxx> > Co-Developed-by: Maxim Popov <maxim.snafu@xxxxxxxxx> > Cc: stable@xxxxxxxxxxxxxxx I tested your patch for the last few days, and I was not able to reproduce the problem (I put a trace to detect the condition). But at the same time, it has not caused any regressions. With the above changes, feel free to add: Tested by: Hugo Villeneuve <hvilleneuve@xxxxxxxxxxxx> Hugo. > --- > Meanwhile, NXP has confirmed this fix to be correct. > > v4: NXP has confirmed the fix; update the commit log accordingly > v3: re-added the additional Co-Developed-by and stable@ tags > v2: reworded the commit log a bit for more context. > > 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 > >
