Re: [PATCH V8 5/9] pci, acpi: add acpi hook to assign domain number.

Bjorn Helgaas
2016-06-08T00:16:07Z

Hi Tomasz,

On Mon, May 30, 2016 at 05:14:18PM +0200, Tomasz Nowicki wrote:
> PCI core code provides a config option (CONFIG_PCI_DOMAINS_GENERIC)
> that allows assigning the PCI bus domain number generically by
> relying on device tree bindings, and falling back to a simple counter
> when the respective DT properties (ie "linux,pci-domain") are not
> specified in the host bridge device tree node.
>
> In a similar way, when a system is booted through ACPI, architectures
> that are selecting CONFIG_PCI_DOMAINS_GENERIC (ie ARM64) require kernel
> hooks to retrieve the domain number so that the PCI bus domain number
> set-up can be handled seamlessly with DT and ACPI in generic core code
> when CONFIG_PCI_DOMAINS_GENERIC is selected.
>
> Since currently it is not possible to retrieve a pointer to the PCI
> host bridge ACPI device backing the host bridge from core PCI code
> (which would allow retrieving the domain number in an arch agnostic
> way through the ACPI _SEG method), an arch specific ACPI hook has to
> be declared and implemented by all arches that rely on
> CONFIG_PCI_DOMAINS_GENERIC to retrieve the domain number and set it
> up in core PCI code.
>
> For the aforementioned reasons, this patch introduces a dummy
> acpi_pci_bus_domain_nr() hook in preparation for per-arch implementation
> of the same to retrieve the domain number on a per-arch basis when
> the system boots through ACPI.
>
> For the sake of code clarity the current code implementing generic
> domain number assignment (ie pci_bus_assign_domain_nr(), selected by
> CONFIG_PCI_DOMAINS_GENERIC) is reshuffled so that the code implementing
> the DT domain assignment function is stubbed out into a corresponding
> helper, so that DT and ACPI functions are clearly separated in
> preparation for arches acpi_pci_bus_domain_nr() implementations.
>
> Signed-off-by: Tomasz Nowicki <tn@semihalf.com>
> Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
> ---
> drivers/pci/pci.c | 11 +++++++++--
> include/linux/pci.h | 1 +
> 2 files changed, 10 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> index eb431b5..2b52178 100644
> --- a/drivers/pci/pci.c
> +++ b/drivers/pci/pci.c
> @@ -7,6 +7,7 @@
> * Copyright 1997 -- 2000 Martin Mares <mj@ucw.cz>
> */
>
> +#include <linux/acpi.h>
> #include <linux/kernel.h>
> #include <linux/delay.h>
> #include <linux/init.h>
> @@ -4941,7 +4942,7 @@ int pci_get_new_domain_nr(void)
> }
>
> #ifdef CONFIG_PCI_DOMAINS_GENERIC
> -void pci_bus_assign_domain_nr(struct pci_bus *bus, struct device *parent)
> +static int of_pci_bus_domain_nr(struct device *parent)

Can we do a little cleanup before this patch?

- pci_bus_assign_domain_nr() is only used inside drivers/pci, so
maybe we move the prototype to drivers/pci/pci.h?

- I don't really like the style of calling a function that
internally assigns bus->domain_nr. Could we do something like
this instead?

int pci_bus_domain_nr(...)
{
...
return domain;
}

... pci_create_root_bus(...)
{
...
b->domain_nr = pci_bus_domain_nr(...);

That would be two new patches, if this makes sense.

And this patch would only rename pci_bus_assign_domain_nr() to
of_pci_bus_domain_nr() and add the pci_bus_domain_nr() wrapper.

> {
> static int use_dt_domains = -1;
> int domain = -1;
> @@ -4985,7 +4986,13 @@ void pci_bus_assign_domain_nr(struct pci_bus *bus, struct device *parent)
> domain = -1;
> }
>
> - bus->domain_nr = domain;
> + return domain;
> +}
> +
> +void pci_bus_assign_domain_nr(struct pci_bus *bus, struct device *parent)
> +{
> + bus->domain_nr = acpi_disabled ? of_pci_bus_domain_nr(parent) :
> + acpi_pci_bus_domain_nr(bus);
> }
> #endif
> #endif
> diff --git a/include/linux/pci.h b/include/linux/pci.h
> index 12349de..bba4053 100644
> --- a/include/linux/pci.h
> +++ b/include/linux/pci.h
> @@ -1390,6 +1390,7 @@ static inline int pci_domain_nr(struct pci_bus *bus)
> {
> return bus->domain_nr;
> }
> +static inline int acpi_pci_bus_domain_nr(struct pci_bus *bus) { return -1; }

I would split the addition of acpi_pci_bus_domain_nr() to a separate
patch and include the ARM64 definition in that same patch. That patch
would only add this stub definition, the ARM64 definition, and the new
call in pci_bus_domain_nr().

> void pci_bus_assign_domain_nr(struct pci_bus *bus, struct device *parent);
> #else
> static inline void pci_bus_assign_domain_nr(struct pci_bus *bus,
> --
> 1.9.1
>