Re: [PATCH v4] PCI: Disable broken FLR on MediaTek MT7925

[Bjorn Helgaas <helgaas@kernel.org>]

[cc list trimmed]

On Tue, Jun 09, 2026 at 06:36:38AM -0700, manisadhasivam.linux@gmail.com wrote:
> On Fri, 22 May 2026 09:06:46 +0200, Jose Ignacio Tornos Martinez
> <jtornosm@redhat.com> said:
> > The MediaTek MT7925 WiFi device advertises FLR capability, but it does
> > not work correctly. This manifests in VFIO passthrough scenarios: normal
> > VM operation works fine, including clean shutdown/reboot. However, when
> > the VM terminates uncleanly (crash, force-off), VFIO attempts to reset
> > the device before it can be assigned to another VM. Because FLR is broken,
> > the reset fails preventing reuse.
> >
> > This is similar to its predecessor MT7922 (see commit 81f64e925c29 ("PCI:
> > Avoid FLR for Mediatek MT7922 WiFi")), but with different symptoms.
> > The MT7922 issue manifests as config read failures (returning ~0) after
> > FLR. The MT7925 shows different behavior: config reads work correctly
> > after FLR, but firmware communication fails.
> >
> > First VM start with MT7925 works fine:
> >   mt7925e 0000:08:00.0: ASIC revision: 79250000
> >   mt7925e 0000:08:00.0: WM Firmware Version: ____000000, Build Time:
> >     20260106153120
> >
> > After force reset or VM crash, when VFIO attempts FLR to reset the device
> > for reassignment, firmware initialization fails:
> >   mt7925e 0000:08:00.0: ASIC revision: 79250000
> >   mt7925e 0000:08:00.0: Message 00000010 (seq 1) timeout
> >   mt7925e 0000:08:00.0: Failed to get patch semaphore
> >   [Repeats with increasing sequence numbers 2-10]
> >   mt7925e 0000:08:00.0: hardware init failed
> >
> > The driver cannot acquire the patch semaphore needed for firmware
> > initialization, indicating that FLR does not properly reset the firmware
> > state. The device remains in this broken state until physical power cycle.
> >
> > Disable FLR for MT7925 so the PCI core falls back to Secondary Bus Reset,
> > which successfully resets the device and allows reinitialization for VFIO
> > passthrough reuse.
> >
> > Signed-off-by: Jose Ignacio Tornos Martinez <jtornosm@redhat.com>
> 
> Reviewed-by: Manivannan Sadhasivam <mani@kernel.org>

Just FYI, b4 complains:

  NOTE: some trailers ignored due to from/email mismatches:
      ! Trailer: Reviewed-by: Manivannan Sadhasivam <mani@kernel.org>
       Msg From: manisadhasivam.linux@gmail.com <manisadhasivam.linux@gmail.com>

I applied your R-b manually.