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

[Alex Williamson]

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