linux-kernel - Re: [PATCH v7 06/17] ARM64 / ACPI: Make PCI optional for ACPI on ARM64

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Message-ID: <20150120110045.GD25575@e104818-lin.cambridge.arm.com>
Date:	Tue, 20 Jan 2015 11:00:45 +0000
From:	Catalin Marinas <catalin.marinas@....com>
To:	Hanjun Guo <hanjun.guo@...aro.org>
Cc:	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Olof Johansson <olof@...om.net>, Arnd Bergmann <arnd@...db.de>,
	Mark Rutland <Mark.Rutland@....com>,
	"grant.likely@...aro.org" <grant.likely@...aro.org>,
	Will Deacon <Will.Deacon@....com>,
	Lorenzo Pieralisi <Lorenzo.Pieralisi@....com>,
	"graeme.gregory@...aro.org" <graeme.gregory@...aro.org>,
	Sudeep Holla <Sudeep.Holla@....com>,
	"jcm@...hat.com" <jcm@...hat.com>,
	Jason Cooper <jason@...edaemon.net>,
	Marc Zyngier <Marc.Zyngier@....com>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Mark Brown <broonie@...nel.org>, Rob Herring <robh@...nel.org>,
	Robert Richter <rric@...nel.org>,
	Randy Dunlap <rdunlap@...radead.org>,
	Charles Garcia-Tobin <Charles.Garcia-Tobin@....com>,
	"phoenix.liyi@...wei.com" <phoenix.liyi@...wei.com>,
	Timur Tabi <timur@...eaurora.org>,
	"suravee.suthikulpanit@....com" <suravee.suthikulpanit@....com>,
	"wangyijing@...wei.com" <wangyijing@...wei.com>,
	"linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linaro-acpi@...ts.linaro.org" <linaro-acpi@...ts.linaro.org>
Subject: Re: [PATCH v7 06/17] ARM64 / ACPI: Make PCI optional for ACPI on
 ARM64

On Tue, Jan 20, 2015 at 02:39:16AM +0000, Hanjun Guo wrote:
> On 2015年01月19日 18:42, Catalin Marinas wrote:
> > On Sun, Jan 18, 2015 at 06:25:53AM +0000, Hanjun Guo wrote:
> >> On 2015年01月16日 17:49, Catalin Marinas wrote:
> >>> On Wed, Jan 14, 2015 at 03:04:54PM +0000, Hanjun Guo wrote:
> >>>> --- a/arch/arm64/kernel/pci.c
> >>>> +++ b/arch/arm64/kernel/pci.c
> >>>> @@ -10,6 +10,7 @@
> >>>>     *
> >>>>     */
> >>>>
> >>>> +#include <linux/acpi.h>
> >>>>    #include <linux/init.h>
> >>>>    #include <linux/io.h>
> >>>>    #include <linux/kernel.h>
> >>>> @@ -68,3 +69,30 @@ void pci_bus_assign_domain_nr(struct pci_bus *bus, struct device *parent)
> >>>>    	bus->domain_nr = domain;
> >>>>    }
> >>>>    #endif
> >>>> +
> >>>> +/*
> >>>> + * raw_pci_read/write - Platform-specific PCI config space access.
> >>>> + *
> >>>> + * Default empty implementation.  Replace with an architecture-specific setup
> >>>> + * routine, if necessary.
> >>>> + */
> >>>> +int raw_pci_read(unsigned int domain, unsigned int bus,
> >>>> +		  unsigned int devfn, int reg, int len, u32 *val)
> >>>> +{
> >>>> +	return -EINVAL;
> >>>> +}
> >>>> +
> >>>> +int raw_pci_write(unsigned int domain, unsigned int bus,
> >>>> +		unsigned int devfn, int reg, int len, u32 val)
> >>>> +{
> >>>> +	return -EINVAL;
> >>>> +}
> >>>> +
> >>>> +#ifdef CONFIG_ACPI
> >>>> +/* Root bridge scanning */
> >>>> +struct pci_bus *pci_acpi_scan_root(struct acpi_pci_root *root)
> >>>> +{
> >>>> +	/* TODO: Should be revisited when implementing PCI on ACPI */
> >>>> +	return NULL;
> >>>> +}
> >>>> +#endif
> > [...]
> >>> When PCI is enabled and the above functions are compiled in, do they
> >>> need to return any useful data or just -EINVAL. Are they ever called?
> >>
> >> They will be called if PCI root bridge is defined in DSDT, should I
> >> print some warning message before it is implemented?
> >
> > My point: do they need to return real data when a PCI root bridge is
> > defined in DSDT or you always expect them to always return some -E*? Can
> > you explain why?
> 
> Not always return -E* or NULL;
> 
> For raw_pci_read/write(), they are needed to access the PCI config space
> before the PCI root bus is created. so they will return 0 if access to
> PCI config space is ok; pci_acpi_scan_root() will return root bus
> pointer if it is successfully created.

OK. So what's the plan for implementing these functions properly. For
the raw_pci_read/write, the comment states "replace with an
architecture-specific setup routine". What does this mean?

For pci_acpi_scan_root(), at least the comment states a "TODO". Is there
anyone working on this or we don't expect servers with PCIe soon?

-- 
Catalin
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