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

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Date:	Fri, 13 May 2016 16:55:48 +0530
From:	Jayachandran C <jchandra@...adcom.com>
To:	Tomasz Nowicki <tn@...ihalf.com>
Cc:	Bjorn Helgaas <helgaas@...nel.org>, Arnd Bergmann <arnd@...db.de>,
	Will Deacon <will.deacon@....com>,
	Catalin Marinas <catalin.marinas@....com>,
	Rafael Wysocki <rafael@...nel.org>,
	Hanjun Guo <hanjun.guo@...aro.org>,
	Lorenzo Pieralisi <Lorenzo.Pieralisi@....com>,
	Sinan Kaya <okaya@...eaurora.org>,
	robert.richter@...iumnetworks.com, Marcin Wojtas <mw@...ihalf.com>,
	Liviu.Dudau@....com, David Daney <ddaney@...iumnetworks.com>,
	Wangyijing <wangyijing@...wei.com>,
	Suravee Suthikulanit <Suravee.Suthikulpanit@....com>,
	Mark Salter <msalter@...hat.com>,
	Linux PCI <linux-pci@...r.kernel.org>,
	linux-arm-kernel@...ts.infradead.org,
	ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linaro-acpi@...ts.linaro.org, Jon Masters <jcm@...hat.com>,
	Andrea Gallo <andrea.gallo@...aro.org>,
	Duc Dang <dhdang@....com>, jeremy.linton@....com,
	liudongdong3@...wei.com, Christopher Covington <cov@...eaurora.org>
Subject: Re: [PATCH V7 08/11] pci, acpi: Support for ACPI based generic PCI
 host controller

On Tue, May 10, 2016 at 8:49 PM, Tomasz Nowicki <tn@...ihalf.com> 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@...ihalf.com>
> Signed-off-by: Jayachandran C <jchandra@...adcom.com>
> ---
[....]

> 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.

JC.