Re: [PATCH v2] PCI: Force PM reset for Qualcomm devices with NoSoftRst+

[Jose Ignacio Tornos Martinez <jtornosm@redhat.com>]

Hello Alex,

Thank you again for your detailed feedback and help

>>> What does reset_methods sysfs attribute report for these devices on an
>>> unpatched kernel?
Sorry for my earlier confusion about CONFIG_PCI_RESET_SYSFS - I now understand
the reset_method sysfs file has been available for a long time without any
config option.

Testing confirms only "bus" reset is available on default kernel for these
Qualcomm devices. PM reset returns -ENOTTY (blocked by NoSoftRst+ flag), and
FLR is not advertised. This confirms the default kernel has no working reset
method for these devices.

> Then why aren't we setting quirks to use quirk_no_bus_reset() for these
> devices?
You're right. I am going to try quirk_no_bus_reset() to disable the broken
SBR method.

> PS - D3cold might be an interesting reset method that could be implemented
> for single function endpoints in slots that support it.
I like the suggestion, I am going to implement a generic d3cold as a general
PCI core reset method for single-function devices (not only for Qualcomm).
I have seen that using pci_set_power_state(dev, PCI_D3cold), if no _PR3
support by the platform, it will use D3hot fallback.

The combination of quirk_no_bus_reset() + general d3cold reset method can
provide a much better solution for these devices and the new reset method
allows the configuration if necessary.
I'll send a next version with this.

Thanks

Best regards
José Ignacio