Re: [PATCH V7 08/11] pci, acpi: Support for ACPI based generic PCI host controller

[Tomasz Nowicki]

On 13.05.2016 13:31, Rafael J. Wysocki wrote:
> On Fri, May 13, 2016 at 1:25 PM, Jayachandran C <jchandra@xxxxxxxxxxxx> wrote:
> > On Tue, May 10, 2016 at 8:49 PM, Tomasz Nowicki <tn@xxxxxxxxxxxx> wrote:
> > > This patch is going to implement generic PCI host controller for
> > > ACPI world, similar to what pci-host-generic.c driver does for DT world.
> > >
> > > All such drivers, which we have seen so far, were implemented within
> > > arch/ directory since they had some arch assumptions (x86 and ia64).
> > > However, they all are doing similar thing, so it makes sense to find
> > > some common code and abstract it into the generic driver.
> > >
> > > In order to handle PCI config space regions properly, we define new
> > > MCFG interface which does sanity checks on MCFG table and keeps its
> > > root pointer. User is able to lookup MCFG regions based on that root
> > > pointer and specified domain:bus_start:bus_end touple. We are using
> > > pci_mmcfg_late_init old prototype to avoid another function name.
> > >
> > > The implementation of pci_acpi_scan_root() looks up the MCFG entries
> > > and sets up a new mapping (regions are not mapped until host controller ask
> > > for it). Generic PCI functions are used for accessing config space.
> > > Driver selects PCI_ECAM and uses functions from drivers/pci/ecam.h
> > > to create and access ECAM mappings.
> > >
> > > As mentioned in Kconfig help section, ACPI_PCI_HOST_GENERIC choice
> > > should be made on a per-architecture basis.
> > >
> > > Signed-off-by: Tomasz Nowicki <tn@xxxxxxxxxxxx>
> > > Signed-off-by: Jayachandran C <jchandra@xxxxxxxxxxxx>
> > > ---
> > [....]
> >
> > > diff --git a/drivers/pci/ecam.h b/drivers/pci/ecam.h
> > > index 1ad2176..1cccf57 100644
> > > --- a/drivers/pci/ecam.h
> > > +++ b/drivers/pci/ecam.h
> > > @@ -45,6 +45,11 @@ struct pci_config_window {
> > >                  void __iomem            *win;   /* 64-bit single mapping */
> > >                  void __iomem            **winp; /* 32-bit per bus mapping */
> > >          };
> > > +#ifdef CONFIG_ACPI_PCI_HOST_GENERIC
> > > +       struct acpi_device              *companion; /* ACPI companion device */
> > > +#endif
> > > +       int                             domain;
> > > +
> > >   };
> >
> > Using struct pci_config_window to pass along domain and
> > companion looks bad.  I think there are two possible options
> > to do this better:
> >
> > 1. add a 'struct fwnode_handle *' or 'struct device *parent_dev'
> >     instead of the companion and domain fields above. In case of
> >     ACPI either of them can be used to get the acpi_device and
> >     both  domain and companion can be set from that.
> >
> > 2. make pci_config_window fully embeddable by moving allocation
> >     out of pci_ecam_create to its callers. Then it can be embedded
> >     into acpi_pci_generic_root_info, and container_of can be used
> >     to get acpi info from ->sysdata.
> >
> > The first option should be easier to implement but the second may
> > be better on long run. I would leave it to the Bjorn or Rafael to
> > suggest which is preferred.
>
> Personally, I'd probably try to use fwnode_handle, but the second
> option makes sense too in principle.

Thanks for suggestions. I will try to use fwnode_handle

Tomasz