On Thu, Jul 29, 2021 at 06:25:54PM +0300, Andy Shevchenko wrote:

On Thu, Jul 29, 2021 at 11:37 AM Ralf Ramsauer
[off-list ref] wrote:

quoted

On 29/07/2021 06:33, Mario Kleiner wrote:

quoted

This attempts to fix a bug found with a serial port card which uses
an MCS9922 chip, one of the 4 models for which MSI-X interrupts are
currently supported. I don't possess such a card, and i'm not
experienced with the serial subsystem, so this patch is based on what
i think i found as a likely reason for failure, based on walking the
user who actually owns the card through some diagnostic.

As there's currently some (stuck) discussion on how to generally handle
MSI capable serial cards, and this is issue related to some degree, let
me Cc Jiri and Andy.

Thanks, Ralf!

quoted

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The user who reported the problem finds the following in his dmesg
output for the relevant ttyS4 and ttyS5:

[    0.580425] serial 0000:02:00.0: enabling device (0000 -> 0003)
[    0.601448] 0000:02:00.0: ttyS4 at I/O 0x3010 (irq = 125, base_baud = 115200) is a ST16650V2
[    0.603089] serial 0000:02:00.1: enabling device (0000 -> 0003)
[    0.624119] 0000:02:00.1: ttyS5 at I/O 0x3000 (irq = 126, base_baud = 115200) is a ST16650V2
...
[    6.323784] genirq: Flags mismatch irq 128. 00000080 (ttyS5) vs. 00000000 (xhci_hcd)
[    6.324128] genirq: Flags mismatch irq 128. 00000080 (ttyS5) vs. 00000000 (xhci_hcd)
...

Output of setserial -a:

/dev/ttyS4, Line 4, UART: 16650V2, Port: 0x3010, IRQ: 127
      Baud_base: 115200, close_delay: 50, divisor: 0
      closing_wait: 3000
      Flags: spd_normal skip_test

This suggests to me that the serial driver wants to register and share a
MSI/MSI-X irq 128 with the xhci_hcd driver, whereas the xhci driver does
not want to share the irq, as flags 0x00000080 (== IRQF_SHARED) from the
serial port driver means to share the irq, and this mismatch ends in some
failed irq init?

With this setup, data reception works very unreliable, with dropped data,
already at a transmission rate of only a 16 Bytes chunk every 1/120th of
a second, ie. 1920 Bytes/sec, presumably due to rx fifo overflow due to
mishandled or not used at all rx irq's?

See full discussion thread with attempted diagnosis at:

https://psychtoolbox.discourse.group/t/issues-with-iscan-serial-port-recording/3886

Disabling the use of MSI interrupts for the serial port pci card did
fix the reliability problems. The user executed the following sequence
of commands to achieve this:

# Disable PCI serial port driver, shut down card:
echo 0000:02:00.0 | sudo tee /sys/bus/pci/drivers/serial/unbind
echo 0000:02:00.1 | sudo tee /sys/bus/pci/drivers/serial/unbind

# Disallow use of MSI/MSI-X interrupts on pci serial port card:
echo 0 | sudo tee /sys/bus/pci/devices/0000:02:00.0/msi_bus
echo 0 | sudo tee /sys/bus/pci/devices/0000:02:00.1/msi_bus

# Restart driver, reinitialize card, hopefully without MSI irqs now:
echo 0000:02:00.0 | sudo tee /sys/bus/pci/drivers/serial/bind
echo 0000:02:00.1 | sudo tee /sys/bus/pci/drivers/serial/bind

This resulted in the following log output:

[   82.179021] pci 0000:02:00.0: MSI/MSI-X disallowed for future drivers
[   87.003031] pci 0000:02:00.1: MSI/MSI-X disallowed for future drivers
[   98.537010] 0000:02:00.0: ttyS4 at I/O 0x3010 (irq = 17, base_baud = 115200) is a ST16650V2
[  103.648124] 0000:02:00.1: ttyS5 at I/O 0x3000 (irq = 18, base_baud = 115200) is a ST16650V2

This patch attempts to fix the problem by disabling irq sharing when
using MSI irq's. Note that all i know for sure is that disabling MSI

In general the shared MSI interrupts are weird things that can be done
with IRQs.

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irq's fixed the problem for the user, so this patch could be wrong and
is untested. Please review with caution, keeping this in mind.

I think it's a good idea in general. I have no objections.

So is that a "reviewed-by" for this patch?

thanks,

greg k-h