Re: [PATCH v11 4/9] PCI: Add additional checks for flr reset

[Farhan Ali]

On 3/25/2026 9:25 AM, Alex Williamson wrote:
> On Tue, 24 Mar 2026 17:49:36 -0500
> Bjorn Helgaas <helgaas@xxxxxxxxxx> wrote:
>
> > On Mon, Mar 16, 2026 at 12:15:39PM -0700, Farhan Ali wrote:
> > > If a device is in an error state, then any reads of device registers can
> > > return error value. Add additional checks to validate if a device is in an
> > > error state before doing an flr reset.
> > s/flr/FLR/ (also in subject)
> >
> > Also please extend the subject to say something specific about the
> > "additional checks".  E.g.,
> >
> >    PCI: Fail FLR when config space inaccessible
> >
> > > Cc: stable@xxxxxxxxxxxxxxx
> > > Reviewed-by: Benjamin Block <bblock@xxxxxxxxxxxxx>
> > > Reviewed-by: Niklas Schnelle <schnelle@xxxxxxxxxxxxx>
> > > Signed-off-by: Farhan Ali <alifm@xxxxxxxxxxxxx>
> > > ---
> > >   drivers/pci/pci.c | 7 +++++++
> > >   1 file changed, 7 insertions(+)
> > >
> > > diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> > > index 373421f4b9d8..8e4d924f4e88 100644
> > > --- a/drivers/pci/pci.c
> > > +++ b/drivers/pci/pci.c
> > > @@ -4371,12 +4371,19 @@ EXPORT_SYMBOL_GPL(pcie_flr);
> > >    */
> > >   int pcie_reset_flr(struct pci_dev *dev, bool probe)
> > >   {
> > > +	u32 reg;
> > > +
> > >   	if (dev->dev_flags & PCI_DEV_FLAGS_NO_FLR_RESET)
> > >   		return -ENOTTY;
> > >   
> > >   	if (!(dev->devcap & PCI_EXP_DEVCAP_FLR))
> > >   		return -ENOTTY;
> > >   
> > > +	if (pcie_capability_read_dword(dev, PCI_EXP_DEVCAP, &reg)) {
> > > +		pci_warn(dev, "Device unable to do an FLR\n");
> > > +		return -ENOTTY;
> > > +	}
> > I guess the point of this is to detect devices that are inaccessible?
> > The same sort of thing as in pci_dev_save_and_disable() from patch
> > 3/9?  But we use "dev->error_state == pci_channel_io_perm_failure"
> > instead?
> >
> > No matter what we do, this has the same race as in patch 3/9.  And I
> > think using dev->error_state also depends on AER being enabled, which
> > cuts out many PCIe devices.
> >
> > I think using the same exact code as in pci_dev_save_and_disable()
> > would be more straightforward.  And also the same sort of wording in
> > the message, e.g., "Device config space inaccessible; unable to FLR"
> > or similar.  I foresee many of these messages in my future, and it
> > will be helpful to have a specific clue about why FLR failed :)
> I think pci_af_flr() and pci_pm_reset() are all subject to this as
> well, some of the device specific resets too.  Maybe we need a common
> helper with a string provided so we can differentiate the callers, even
> if we don't make all the conversions in this series.  Thanks,
>
> Alex

Yeah I was planning on implementing a common function in the next 
revision. Will include a string parameter to differentiate the callers. 
And yeah I prefer not to update pci_af_flr() or pci_pm_reset() as part 
of this series since I don't have the devices to test those paths.

Thanks

Farhan