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

Myron Stowe
2014-11-21T04:00:23Z

On Thu, Nov 20, 2014 at 3:26 PM, Bjorn Helgaas <bhelgaas@google.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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