linux-kernel - Re: [PATCH 6/6] pci, acpi: Share ACPI PCI config space accessors.

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Message-ID: <CAL-B5D3MqUa-=bzebo12DbZfczss2-MdGwQ8WKTbFH8H2AENXg@mail.gmail.com>
Date:	Thu, 20 Nov 2014 21:00:17 -0700
From:	Myron Stowe <myron.stowe@...il.com>
To:	Bjorn Helgaas <bhelgaas@...gle.com>
Cc:	Arnd Bergmann <arnd@...db.de>,
	linux-arm-kernel@...ts.infradead.org,
	Tomasz Nowicki <tomasz.nowicki@...aro.org>,
	catalin.marinas@....com, will.deacon@....com,
	lorenzo.pieralisi@....com, wangyijing@...wei.com,
	hanjun.guo@...aro.org, Liviu.Dudau@....com,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, rjw@...ysocki.net,
	linaro-acpi@...ts.linaro.org,
	linux-pci <linux-pci@...r.kernel.org>, x86 <x86@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	"linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>
Subject: Re: [PATCH 6/6] pci, acpi: Share ACPI PCI config space accessors.

On Thu, Nov 20, 2014 at 3:26 PM, Bjorn Helgaas <bhelgaas@...gle.com> wrote:
> On Wed, Nov 19, 2014 at 05:19:20PM +0100, Arnd Bergmann wrote:
>> On Wednesday 19 November 2014 17:04:51 Tomasz Nowicki wrote:
>> > +/*
>> > + * raw_pci_read/write - ACPI PCI config space accessors.
>> > + *
>> > + * ACPI spec defines MMCFG as the way we can access PCI config space,
>> > + * so let MMCFG be default (__weak).
>> > + *
>> > + * If platform needs more fancy stuff, should provides its own implementation.
>> > + */
>> > +int __weak raw_pci_read(unsigned int domain, unsigned int bus,
>> > +                       unsigned int devfn, int reg, int len, u32 *val)
>> > +{
>> > +       return pci_mmcfg_read(domain, bus, devfn, reg, len, val);
>> > +}
>> > +
>> > +int __weak raw_pci_write(unsigned int domain, unsigned int bus,
>> > +                        unsigned int devfn, int reg, int len, u32 val)
>> > +{
>> > +       return pci_mmcfg_write(domain, bus, devfn, reg, len, val);
>> > +}
>> > +
>> >
>>
>> I think it would be better to avoid __weak functions here, as they tend
>> to be hard to follow when trying to understand the code.
>
> That's interesting.  I would have said exactly the opposite -- I think the
> extra Kconfiggery is harder to follow than weak/strong functions :)
>
> But consistency is better than my personal opinion.  Is there a consensus
> that we should use the Kconfig strategy instead of __weak?

I too find weak/strong functions easier to follow than "Kconfiggery" (nice term
invention there).

>
>> How about using a Kconfig symbol like this:
>>
>> #ifdef CONFIG_ARCH_RAW_PCI_READWRITE
>> int raw_pci_read(unsigned int domain, unsigned int bus, unsigned int devfn,
>>                  int reg, int len, u32 *val);
>> int raw_pci_write(unsigned int domain, unsigned int bus, unsigned int devfn,
>>                   int reg, int len, u32 val);
>> #else
>> static inline int raw_pci_read(unsigned int domain, unsigned int bus,
>>                              unsigned int devfn, int reg, int len, u32 *val)
>> {
>>       return pci_mmcfg_read(domain, bus, devfn, reg, len, val);
>> }
>>
>> static inline int raw_pci_write(unsigned int domain, unsigned int bus,
>>                                       unsigned int devfn, int reg, int len, u32 val)
>> {
>>        return pci_mmcfg_write(domain, bus, devfn, reg, len, val);
>> }
>> #endif
> --
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