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

From: Bjorn Helgaas <helgaas@kernel.org>
To: "Pali Rohár" <pali@kernel.org>
Cc: "Lorenzo Pieralisi" <lorenzo.pieralisi@arm.com>,
	"Bjorn Helgaas" <bhelgaas@google.com>,
	"Rob Herring" <robh+dt@kernel.org>,
	"Andrew Lunn" <andrew@lunn.ch>,
	"Thomas Petazzoni" <thomas.petazzoni@bootlin.com>,
	"Krzysztof Wilczyński" <kw@linux.com>,
	"Marek Behún" <kabel@kernel.org>,
	"Russell King" <rmk+kernel@armlinux.org.uk>,
	"Gregory Clement" <gregory.clement@bootlin.com>,
	linux-pci@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH 2/6] PCI: Add PCI_EXP_SLTCAP_*_SHIFT macros
Date: Fri, 25 Feb 2022 09:37:56 -0600	[thread overview]
Message-ID: <20220225153756.GA358517@bhelgaas> (raw)
In-Reply-To: <20220225122451.fa2fiyzohwme2d66@pali>

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