On Thu, 30 Mar 2023 11:26:30 +0300 Ido Schimmel <idosch@xxxxxxxxxx> wrote: > On Wed, Mar 29, 2023 at 11:10:01AM -0600, Alex Williamson wrote: > > I think we don't have it because it's unclear how it's actually > > different from a secondary bus reset from the bridge control register, > > which is what "bus" would do when selected for the example above. Per > > the spec, both must cause a hot reset. It seems this device needs a > > significantly longer delay though. > > Assuming you are referring to the 2ms sleep in > pci_reset_secondary_bus(), then yes. In our case, after disabling the > link on the downstream port we need to wait for 500ms before enabling > it. > > > Note that hot resets can be generated by a userspace driver with > > ownership of the device and will make use of the pci-core reset > > mechanisms. Therefore if there is not a device specific reset, we'll > > use the standard delays and the device ought not to get itself wedged > > if the link becomes active at an unexpected point relative to a > > firmware update. This might be a point in favor of a device specific > > reset solution in pci-core. Thanks, > > I assume you referring to something like this: > > # echo 1 > /sys/class/pci_bus/0000:03/device/0000:03:00.0/reset > > Doesn't seem to have any effect (network ports remain up, at least). > Anyway, this device is completely managed by the kernel, not a user > space driver. I'm not aware of anyone using this method to reset the > device. The pci-sysfs reset attribute is only meant to reset the linked device, so if this is a single function device then it might be accessing bus reset, but it also might be using FLR or PM reset. There's a reset_method attribute to determine and select. In any case, if the device is unaffected, that suggests we're dealing with a device that doesn't comply with PCIe reset standards, which might suggests it needs a device specific reset or to flag broken reset methods regardless. Note that QEMU is a vfio-pci userspace driver, so assigning the device to a VM, where kernel drivers in the guest are managing the device is a use case of userspace drivers which should have a functional reset mechanism to avoid data leakage between userspace sessions. > If I understand Bjorn and you correctly, we have two options: > > 1. Keep the current implementation inside the driver. > > 2. Call __pci_reset_function_locked() from the driver and move the link > toggling to drivers/pci/quirks.c as a "device_specific" method. > > Personally, I don't see any benefit in 2, but we can try to implement > it, see if it even works and then decide. The second option enables use cases like above, where the PCI-core can perform an effective reset of the device rather than embedding that into a specific driver. Even if not intended as a primary use case, it's a more complete solution and avoids potentially unhappy users that assume such use cases are available. Thanks, Alex
