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

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Date:   Thu, 23 Mar 2023 16:30:01 +0200
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     Bjorn Helgaas <helgaas@...nel.org>
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 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.

> > +			r->flags &= ~IORESOURCE_IO;
> > +		if (r->start == 0 && r->end) {
> > +			r->flags = 0;
> > +			r->end = 0;
> >  		}
> >  	}

...

> >  #define pci_resource_len(dev,bar) \
> >  	((pci_resource_end((dev), (bar)) == 0) ? 0 :	\
> >  							\
> > -	 (pci_resource_end((dev), (bar)) -		\
> > -	  pci_resource_start((dev), (bar)) + 1))
> > +	 resource_size(pci_resource_n((dev), (bar))))
> 
> I like this change, but it's unrelated to pci_dev_for_each_resource()
> and unmentioned in the commit log.

And as you rightfully noticed this either. I can split it to a separate one.

...

> > +#define __pci_dev_for_each_resource(dev, res, __i, vartype)		\
> > +	for (vartype __i = 0;						\
> > +	     res = pci_resource_n(dev, __i), __i < PCI_NUM_RESOURCES;	\
> > +	     __i++)
> > +
> > +#define pci_dev_for_each_resource(dev, res, i)				\
> > +       __pci_dev_for_each_resource(dev, res, i, )
> > +
> > +#define pci_dev_for_each_resource_p(dev, res)				\
> > +	__pci_dev_for_each_resource(dev, res, __i, unsigned int)
> 
> This series converts many cases to drop the iterator variable ("i"),
> which is fantastic.
> 
> Several of the remaining places need the iterator variable only to
> call pci_claim_resource(), which could be converted to take a "struct
> resource *" directly without much trouble.
> 
> We don't have to do that pci_claim_resource() conversion now,

Exactly, it's definitely should be separate change.

> 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?

...

> Not sure __pci_dev_for_each_resource() is worthwhile since it only
> avoids repeating that single "for" statement, and passing in "vartype"
> (sometimes empty to implicitly avoid the declaration) is a little
> complicated to read.  I think it'd be easier to read like this:

No objections here.

>   #define pci_dev_for_each_resource(dev, res)                      \
>     for (unsigned int __i = 0;                                     \
>          res = pci_resource_n(dev, __i), __i < PCI_NUM_RESOURCES;  \
>          __i++)
> 
>   #define pci_dev_for_each_resource_idx(dev, res, idx)             \
>     for (idx = 0;                                                  \
>          res = pci_resource_n(dev, idx), idx < PCI_NUM_RESOURCES;  \
>          idx++)

-- 
With Best Regards,
Andy Shevchenko