On Fri, Aug 13, 2021 at 7:45 PM Mario Kleiner <mario.kleiner.de@xxxxxxxxx> wrote: > > Btw., one question to the experts, after much more grepping through > the irq handling code and being no wiser than before: > > My understanding of MSI(-X) is that one of the big advantages over > legacy IRQ is that there are so many available MSI IRQ's, and so IRQ > sharing is normally not needed. So why did the driver choose an MSI > irq shared with the USB host controller? Or iow., why did > > pci_alloc_irq_vectors(dev, 1, 1, PCI_IRQ_ALL_TYPES); and uart.port.irq > = pci_irq_vector(dev, 0); return a IRQ number that was already in use > at that time? Is this something to be expected, or some quirk specific > to serial drivers or this hw? My theory is that they are sharing the same pin on the PCI bus and drivers have a SHARED flag and some code inside IRQ core decides that it's fine to have them shared. But I think the best person to answer is Thomas. > > > > > On 29/07/2021 06:33, Mario Kleiner wrote: > > > > > > 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! > > > > > > > > > > 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. > > > > > > > > > > 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. -- With Best Regards, Andy Shevchenko
