Re: [PATCH v1 1/3] s390/pci: Preserve FMB state in device re-enablement

Niklas Schnelle
2026-05-05T15:49:20Z

On Tue, 2026-05-05 at 17:41 +0200, Niklas Schnelle wrote:
> On Fri, 2026-05-01 at 15:25 -0400, Omar Elghoul wrote:
> > Introduce a function zpci_fmb_reenable_device() that checks for the state
> > of the FMB and reuses the same buffer where appropriate. If FMB was not
> > previously enabled, it enables it for the device. Call this function during
> > a zPCI device re-enablement, which in turn implicitly ensures that the FMB
> > is enabled for host devices during their KVM registration.
> >
> > This function also clears out the software counters, so that a program
> > resetting an FMB would see all its counters restart from zero as expected.
> > The function to clear the software counters is also separated into a static
> > function as it is now reused in both zpci_fmb_enable_device() and
> > zpci_fmb_reenable_device().
> >
> > Signed-off-by: Omar Elghoul <oelghoul@linux.ibm.com>
> > ---
> > arch/s390/include/asm/pci.h | 1 +
> > arch/s390/pci/pci.c | 71 ++++++++++++++++++++++++++++++-------
> > 2 files changed, 59 insertions(+), 13 deletions(-)
> >
>
> Looks good to me. I also gave this a quick sniff test on an LPAR but
> still have to test with the FMB handling for KVM that this enabled so
> not enough for a Tested-by yet.
>
> Still feel free to add my:
>
> Reviewed-by: Niklas Schnelle <schnelle@linux.ibm.com>
>
> Thanks,
> Niklas

Ah, missed one thing, the kernel-test-robot is of course right in that
with this patch flags and ctrs are now unused in
zpci_fmb_enable_device() so the declarations should be dropped. The
same is also true in zpci_fmb_reenable_device() which the test robot
did miss!

Thanks,
Niklas