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 13:31:31 +0200
From:	"Rafael J. Wysocki" <rafael@...nel.org>
To:	Jayachandran C <jchandra@...adcom.com>
Cc:	Tomasz Nowicki <tn@...ihalf.com>,
	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" 
	<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" <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 Fri, May 13, 2016 at 1:25 PM, Jayachandran C <jchandra@...adcom.com> wrote:
> 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.

Personally, I'd probably try to use fwnode_handle, but the second
option makes sense too in principle.