This is a note to let you know that I've just added the patch titled
serial: sc16is7xx: address RX timeout interrupt errata
to the 4.19-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-sc16is7xx-address-rx-timeout-interrupt-errata.patch
and it can be found in the queue-4.19 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 08ce9a1b72e38cf44c300a44ac5858533eb3c860 Mon Sep 17 00:00:00 2001
From: Daniel Mack <daniel@xxxxxxxxxx>
Date: Thu, 23 Nov 2023 08:28:18 +0100
Subject: serial: sc16is7xx: address RX timeout interrupt errata
From: Daniel Mack <daniel@xxxxxxxxxx>
commit 08ce9a1b72e38cf44c300a44ac5858533eb3c860 upstream.
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 description seems to indicate it concerns only polled mode of
operation when reading bit 0 of the LSR register. However, tests have
shown and NXP has confirmed that the RXLVL register also yields 0 when
the bug is triggered, and hence the IRQ driven implementation in this
driver is equally affected.
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 from the FIFO when this condition
is detected in order to clear the interrupt. This approach was
confirmed to be correct by NXP through their support channels.
Tested by: Hugo Villeneuve <hvilleneuve@xxxxxxxxxxxx>
Signed-off-by: Daniel Mack <daniel@xxxxxxxxxx>
Co-Developed-by: Maxim Popov <maxim.snafu@xxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Link: https://lore.kernel.org/r/20231123072818.1394539-1-daniel@xxxxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
drivers/tty/serial/sc16is7xx.c | 12 ++++++++++++
1 file changed, 12 insertions(+)
--- a/drivers/tty/serial/sc16is7xx.c
+++ b/drivers/tty/serial/sc16is7xx.c
@@ -694,6 +694,18 @@ static bool sc16is7xx_port_irq(struct sc
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;
Patches currently in stable-queue which might be from daniel@xxxxxxxxxx are
queue-4.19/serial-sc16is7xx-address-rx-timeout-interrupt-errata.patch
