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

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Message-ID: <20160608001559.GD4759@localhost>
Date:	Tue, 7 Jun 2016 19:15:59 -0500
From:	Bjorn Helgaas <helgaas@...nel.org>
To:	Tomasz Nowicki <tn@...ihalf.com>
Cc:	arnd@...db.de, will.deacon@....com, catalin.marinas@....com,
	rafael@...nel.org, hanjun.guo@...aro.org,
	Lorenzo.Pieralisi@....com, okaya@...eaurora.org,
	jchandra@...adcom.com, robert.richter@...iumnetworks.com,
	mw@...ihalf.com, Liviu.Dudau@....com, ddaney@...iumnetworks.com,
	wangyijing@...wei.com, Suravee.Suthikulpanit@....com,
	msalter@...hat.com, linux-pci@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, linux-acpi@...r.kernel.org,
	linux-kernel@...r.kernel.org, linaro-acpi@...ts.linaro.org,
	jcm@...hat.com, andrea.gallo@...aro.org, dhdang@....com,
	jeremy.linton@....com, liudongdong3@...wei.com, cov@...eaurora.org
Subject: Re: [PATCH V8 5/9] pci, acpi: add acpi hook to assign domain number.

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@...ihalf.com>
> Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@....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@....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
>