Re: [PATCH 2/6] PCI: Add PCI_EXP_SLTCAP_*_SHIFT macros

Bjorn Helgaas
2022-02-25T15:39:49Z

On Fri, Feb 25, 2022 at 01:24:51PM +0100, Pali Rohár wrote:
> On Thursday 24 February 2022 14:28:43 Bjorn Helgaas wrote:
> > On Tue, Feb 22, 2022 at 05:31:54PM +0100, Pali Rohár wrote:
> > > These macros allows to easily compose and extract Slot Power Limit and
> > > Physical Slot Number values from Slot Capability Register.
> > >
> > > Signed-off-by: Pali Rohár <pali@kernel.org>
> > > Signed-off-by: Marek Behún <kabel@kernel.org>
> > > ---
> > > include/uapi/linux/pci_regs.h | 3 +++
> > > 1 file changed, 3 insertions(+)
> > >
> > > diff --git a/include/uapi/linux/pci_regs.h b/include/uapi/linux/pci_regs.h
> > > index 108f8523fa04..3fc9a4cac630 100644
> > > --- a/include/uapi/linux/pci_regs.h
> > > +++ b/include/uapi/linux/pci_regs.h
> > > @@ -591,10 +591,13 @@
> > > #define PCI_EXP_SLTCAP_HPS 0x00000020 /* Hot-Plug Surprise */
> > > #define PCI_EXP_SLTCAP_HPC 0x00000040 /* Hot-Plug Capable */
> > > #define PCI_EXP_SLTCAP_SPLV 0x00007f80 /* Slot Power Limit Value */
> > > +#define PCI_EXP_SLTCAP_SPLV_SHIFT 7 /* Slot Power Limit Value shift */
> >
> > Is there a way to use FIELD_PREP() and FIELD_GET() instead? It seems
> > like that's what the cool kids are doing now.
>
> This is possible too.
>
> I have proposed a patch with _SHIFT macros as this is the way how are
> other macros in this file defined and used.

Yes, it's a mix. For some recent additions, I've resisted adding the
_SHIFT macros on the theory that they clutter the file, they never
change, and the main point of the #defines is readability and so
grep/tags/etc can find things.

There are a *few* users of FIELD_PREP() and FIELD_GET():

git grep -E "FIELD_(GET|PREP)\(PCI_EXP"

and I'm inclined to go that direction in the future. What do you
think?

Bjorn