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

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Date:	Wed, 19 Nov 2014 17:19:20 +0100
From:	Arnd Bergmann <arnd@...db.de>
To:	linux-arm-kernel@...ts.infradead.org
Cc:	Tomasz Nowicki <tomasz.nowicki@...aro.org>,
	catalin.marinas@....com, will.deacon@....com, bhelgaas@...gle.com,
	lorenzo.pieralisi@....com, wangyijing@...wei.com,
	hanjun.guo@...aro.org, Liviu.Dudau@....com, tglx@...utronix.de,
	mingo@...hat.com, hpa@...or.com, rjw@...ysocki.net,
	linaro-acpi@...ts.linaro.org, linux-pci@...r.kernel.org,
	x86@...nel.org, linux-kernel@...r.kernel.org,
	linux-acpi@...r.kernel.org
Subject: Re: [PATCH 6/6] pci, acpi: Share ACPI PCI config space accessors.

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.

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

Same thing for the weak symbols in patch 5.

	Arnd
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