Re: [PATCH v2 1/7] PCI/IOV: Return u16 from pci_sriov_get_totalvfs()

[David Laight <david.laight.linux@gmail.com>]

On Wed, 24 Jun 2026 21:40:52 +0900
"Alexandre Courbot" <acourbot@nvidia.com> wrote:

> On Tue Jun 23, 2026 at 4:43 AM JST, Zhi Wang wrote:
> > pci_sriov_get_totalvfs() reports a VF count, not an errno-style
> > status. It returns 0 when SR-IOV is unavailable or the device is not a
> > PF, and otherwise returns the PF's driver_max_VFs value.
> >
> > driver_max_VFs is stored as a u16 in struct pci_sriov. It is derived
> > from the SR-IOV TotalVFs field or from a driver-provided limit, so the
> > implementation cannot return a negative value.
> >
> > Change the declaration, CONFIG_PCI_IOV stub, and implementation to
> > return u16. Update callers to store the result in u16 variables, remove
> > obsolete negative-value checks, and use unsigned format specifiers where
> > needed.
> >
> > Cc: Bjorn Helgaas <bhelgaas@google.com>
> > Cc: linux-pci@vger.kernel.org
> > Signed-off-by: Zhi Wang <zhiw@nvidia.com>  
> 
> Suggested-by: Alexandre Courbot <acourbot@nvidia.com>
> Link: https://lore.kernel.org/all/DETDILPA1GFY.27WND0TEC5352@nvidia.com/
> 
> > ---
> >  drivers/crypto/hisilicon/qm.c                   | 8 +++++---
> >  drivers/crypto/intel/qat/qat_common/adf_sriov.c | 6 +++---
> >  drivers/gpu/drm/xe/xe_sriov_pf.c                | 6 ++----
> >  drivers/misc/genwqe/card_base.c                 | 6 ++----
> >  drivers/net/ethernet/cavium/thunder/nic_main.c  | 2 +-
> >  drivers/net/ethernet/emulex/benet/be_main.c     | 3 ++-
> >  drivers/net/ethernet/mellanox/mlx5/core/sriov.c | 3 ++-
> >  drivers/net/ethernet/sfc/ef10_sriov.c           | 2 +-  
> 
> I believe that you can avoid converting all these drivers in this patch.
> The implicit `u16 -> int` conversion done by C should result in the
> expected behavior, and it will be fewer Acked-by to collect.

The generated code is also likely to be slightly better if the function
return value is a 32bit value.

Similarly you don't really want to do any kind of maths on local variables
that aren't 32bit (or 64bit on 64bit builds).

The fact that the domain of a value fits in 16 bits doesn't mean that
it is better to use u16 - it is usually worse.
Pretty much the only place u16 should be used is to reduce the size
of structures.

So it is probably correct to change the return type to unsigned int and
remove the error return checks, but nothing else.

	David

> 
> I.e. just updating drivers/pci/iov.c and include/linux/pci.h should be
> sufficient as the first step. Specific drivers can then be updated using
> separate patches that will be easier to merge individually, if you want
> to do so.
>