linux-kernel - Re: [PATCH v6 1/4] PCI: Introduce pci_dev_for_each

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Date:   Thu, 23 Mar 2023 10:02:38 -0500
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc:     Mickaël Salaün <mic@...ikod.net>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>,
        Krzysztof Wilczyński <kw@...ux.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Randy Dunlap <rdunlap@...radead.org>,
        Arnd Bergmann <arnd@...db.de>,
        Niklas Schnelle <schnelle@...ux.ibm.com>,
        "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
        Pali Rohár <pali@...nel.org>,
        "Maciej W. Rozycki" <macro@...am.me.uk>,
        Juergen Gross <jgross@...e.com>,
        Dominik Brodowski <linux@...inikbrodowski.net>,
        linux-kernel@...r.kernel.org, linux-alpha@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-mips@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org, linux-sh@...r.kernel.org,
        sparclinux@...r.kernel.org, linux-pci@...r.kernel.org,
        xen-devel@...ts.xenproject.org, linux-acpi@...r.kernel.org,
        Miguel Ojeda <ojeda@...nel.org>,
        Richard Henderson <richard.henderson@...aro.org>,
        Ivan Kokshaysky <ink@...assic.park.msu.ru>,
        Matt Turner <mattst88@...il.com>,
        Russell King <linux@...linux.org.uk>,
        Andrew Lunn <andrew@...n.ch>,
        Sebastian Hesselbarth <sebastian.hesselbarth@...il.com>,
        Gregory Clement <gregory.clement@...tlin.com>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        Nicholas Piggin <npiggin@...il.com>,
        Christophe Leroy <christophe.leroy@...roup.eu>,
        Anatolij Gustschin <agust@...x.de>,
        Yoshinori Sato <ysato@...rs.sourceforge.jp>,
        Rich Felker <dalias@...c.org>,
        John Paul Adrian Glaubitz <glaubitz@...sik.fu-berlin.de>,
        "David S. Miller" <davem@...emloft.net>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Stefano Stabellini <sstabellini@...nel.org>,
        Oleksandr Tyshchenko <oleksandr_tyshchenko@...m.com>
Subject: Re: [PATCH v6 1/4] PCI: Introduce pci_dev_for_each_resource()

On Thu, Mar 23, 2023 at 04:30:01PM +0200, Andy Shevchenko wrote:
> On Wed, Mar 22, 2023 at 02:28:04PM -0500, Bjorn Helgaas wrote:
> > On Mon, Mar 20, 2023 at 03:16:30PM +0200, Andy Shevchenko wrote:
> ...
> 
> > > +	pci_dev_for_each_resource_p(dev, r) {
> > >  		/* zap the 2nd function of the winbond chip */
> > > -		if (dev->resource[i].flags & IORESOURCE_IO
> > > -		    && dev->bus->number == 0 && dev->devfn == 0x81)
> > > -			dev->resource[i].flags &= ~IORESOURCE_IO;
> > > -		if (dev->resource[i].start == 0 && dev->resource[i].end) {
> > > -			dev->resource[i].flags = 0;
> > > -			dev->resource[i].end = 0;
> > > +		if (dev->bus->number == 0 && dev->devfn == 0x81 &&
> > > +		    r->flags & IORESOURCE_IO)
> > 
> > This is a nice literal conversion, but it's kind of lame to test
> > bus->number and devfn *inside* the loop here, since they can't change
> > inside the loop.
> 
> Hmm... why are you asking me, even if I may agree on that? It's
> in the original code and out of scope of this series.

Yeah, I don't think it would be *unreasonable* to clean this up at the
same time so the maintainers can look at both at the same time (this
is arch/powerpc/platforms/pseries/pci.c, so Michael, et al), but no
need for you to do anything, certainly.  I can post a follow-up patch.

> > but
> > since we're converging on the "(dev, res)" style, I think we should
> > reverse the names so we have something like:
> > 
> >   pci_dev_for_each_resource(dev, res)
> >   pci_dev_for_each_resource_idx(dev, res, i)
> 
> Wouldn't it be more churn, including pci_bus_for_each_resource() correction?

Yes, it definitely is a little more churn because we already have
pci_bus_for_each_resource() that would have to be changed.

I poked around looking for similar patterns elsewhere with:

  git grep "#define.*for_each_.*_p("
  git grep "#define.*for_each_.*_idx("

I didn't find any other "_p" iterators and just a few "_idx" ones, so
my hope is to follow what little precedent there is, as well as
converge on the basic "*_for_each_resource()" iterators and remove the
"_idx()" versions over time by doing things like the
pci_claim_resource() change.

What do you think?  If it seems like excessive churn, we can do it
as-is and still try to reduce the use of the index variable over time.

Bjorn