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

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Message-ID: <20230322192804.GA2485349@bhelgaas>
Date:   Wed, 22 Mar 2023 14:28:04 -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()

Hi Andy and Mika,

I really like the improvements here.  They make the code read much
better.

On Mon, Mar 20, 2023 at 03:16:30PM +0200, Andy Shevchenko wrote:
> From: Mika Westerberg <mika.westerberg@...ux.intel.com>
> ...

>  static void fixup_winbond_82c105(struct pci_dev* dev)
>  {
> -	int i;
> +	struct resource *r;
>  	unsigned int reg;
>  
>  	if (!machine_is(pseries))
> @@ -251,14 +251,14 @@ static void fixup_winbond_82c105(struct pci_dev* dev)
>  	/* Enable LEGIRQ to use INTC instead of ISA interrupts */
>  	pci_write_config_dword(dev, 0x40, reg | (1<<11));
>  
> -	for (i = 0; i < DEVICE_COUNT_RESOURCE; ++i) {
> +	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.

> +			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.

> +#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, 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)

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:

  #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++)

Bjorn