Re: [PATCH V6 02/13] pci, acpi: Provide generic way to assign bus domain number.

[Tomasz Nowicki]

On 27.04.2016 04:26, Bjorn Helgaas wrote:
> On Fri, Apr 15, 2016 at 07:06:37PM +0200, Tomasz Nowicki wrote:
> > As we now have valid PCI host bridge device reference we can
> > introduce code that is going to find its bus domain number using
> > ACPI _SEG method.
> >
> > Note that _SEG method is optional, therefore _SEG absence means
> > that all PCI buses belong to domain 0.
> >
> > While at it, for the sake of code clarity we put ACPI and DT domain
> > assign methods into the corresponding helpers.
> >
> > Signed-off-by: Tomasz Nowicki <tn@xxxxxxxxxxxx>
> > Reviewed-by: Liviu Dudau <Liviu.Dudau@xxxxxxx>
> > Tested-by: Suravee Suthikulpanit <Suravee.Suthikulpanit@xxxxxxx>
> > Tested-by: Jeremy Linton <jeremy.linton@xxxxxxx>
> > Tested-by: Duc Dang <dhdang@xxxxxxx>
> > Tested-by: Dongdong Liu <liudongdong3@xxxxxxxxxx>
> > Tested-by: Hanjun Guo <hanjun.guo@xxxxxxxxxx>
> > Tested-by: Graeme Gregory <graeme.gregory@xxxxxxxxxx>
> > Tested-by: Sinan Kaya <okaya@xxxxxxxxxxxxxx>
> > ---
> >   drivers/acpi/pci_root.c  | 18 ++++++++++++++++++
> >   drivers/pci/pci.c        | 11 +++++++++--
> >   include/linux/pci-acpi.h |  2 ++
> >   3 files changed, 29 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/acpi/pci_root.c b/drivers/acpi/pci_root.c
> > index 4581e0e..d9a70c4 100644
> > --- a/drivers/acpi/pci_root.c
> > +++ b/drivers/acpi/pci_root.c
> > @@ -419,6 +419,24 @@ out:
> >   }
> >   EXPORT_SYMBOL(acpi_pci_osc_control_set);
> >
> > +int acpi_pci_bus_domain_nr(struct device *parent)
> > +{
> > +	struct acpi_device *acpi_dev = to_acpi_device(parent);
> > +	unsigned long long segment = 0;
> > +	acpi_status status;
> > +
> > +	/*
> > +	 * If _SEG method does not exist, following ACPI spec (6.5.6)
> > +	 * all PCI buses belong to domain 0.
> > +	 */
> > +	status = acpi_evaluate_integer(acpi_dev->handle, METHOD_NAME__SEG, NULL,
> > +				       &segment);
>
> We already have code in acpi_pci_root_add() to evaluate _SEG.  We
> don't want to evaluate it *twice*, do we?

Ideally we do not want.

The main intention here was to avoid using "void *sysdata" to retrieve 
domain number. sysdata means something different for each architectures. 
This would be common way for all arch using PCI_DOMAINS_GENERIC option 
such as ARM64.

> I was sort of expecting that if you added it here, we'd remove the
> existing call, but it looks like you're keeping both?

I leave _SEG evaluation in acpi_pci_root_add to keep support for IA64 
and x86 which are still using arch-specific sysdata (struct 
pci_sysdata->domain for x86 and struct pci_controller->segment for IA64) 
to retrieve domain number.

ARM64 uses PCI_DOMAINS_GENERIC for DT boot method, it would be 
consistent to keep it for ACPI too.

I am open to suggestions, do you think we should use sysdata for ARM64?

Thanks,
Tomasz