linux-kernel - Re: [PATCH V6 02/13] pci, acpi: Provide generic way to assign bus domain number.

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Message-ID: <CAKc_7PU1AszF4y0OjZ3KVGaTEx9OL1cuT5YgOxQKhAQgQom7tA@mail.gmail.com>
Date:	Mon, 2 May 2016 18:56:13 +0530
From:	Jayachandran C <jchandra@...adcom.com>
To:	Tomasz Nowicki <tn@...ihalf.com>
Cc:	Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
	Bjorn Helgaas <helgaas@...nel.org>,
	Arnd Bergmann <arnd@...db.de>,
	Will Deacon <will.deacon@....com>,
	Catalin Marinas <catalin.marinas@....com>, rafael@...nel.org,
	Hanjun Guo <hanjun.guo@...aro.org>,
	Sinan Kaya <okaya@...eaurora.org>, jiang.liu@...ux.intel.com,
	robert.richter@...iumnetworks.com, Marcin Wojtas <mw@...ihalf.com>,
	Liviu.Dudau@....com, David Daney <ddaney@...iumnetworks.com>,
	Wangyijing <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, Jon Masters <jcm@...hat.com>
Subject: Re: [PATCH V6 02/13] pci, acpi: Provide generic way to assign bus
 domain number.

On Mon, May 2, 2016 at 6:13 PM, Tomasz Nowicki <tn@...ihalf.com> wrote:
> On 04/27/2016 01:17 PM, Lorenzo Pieralisi wrote:
>>
>> On Tue, Apr 26, 2016 at 09:26:49PM -0500, Bjorn Helgaas wrote:
>>>
>>> On Fri, Apr 15, 2016 at 07:06:37PM +0200, Tomasz Nowicki wrote:
>
> [...]
>
>>>   +int acpi_pci_bus_domain_nr(struct device *parent)
>>> +{
>>> +       struct acpi_device *acpi_dev = to_acpi_device(parent);
>>> +       unsigned long long segment = 0;
>>> +       acpi_status status;
>>> +
>>> +       /*
>>> +        * If _SEG method does not exist, following ACPI spec (6.5.6)
>>> +        * all PCI buses belong to domain 0.
>>> +        */
>>> +       status = acpi_evaluate_integer(acpi_dev->handle,
>>> METHOD_NAME__SEG, NULL,
>>> +                                      &segment);
>>> We already have code in acpi_pci_root_add() to evaluate _SEG.  We
>>> don't want to evaluate it *twice*, do we?
>>>
>>> I was sort of expecting that if you added it here, we'd remove the
>>> existing call, but it looks like you're keeping both?
>>
>> We can't remove the existing call, since it is used on X86 and IA64
>> to store the segment number that, in the process, is used in their
>> pci_domain_nr() arch specific callback to retrieve the domain nr.
>>
>> On ARM64, that selects PCI_DOMAINS_GENERIC, we have to find a way
>> to retrieve the domain number that is not arch dependent, since
>> this is generic code, we can't rely on any bus->sysdata format (unless
>> we do something like JC did below), therefore the only way is to call
>> the _SEG method *again* here, which also forced Tomasz to go through
>> the ACPI_COMPANION setting song and dance and pass the parent pointer
>> to pci_create_root_bus() (see patch 1), which BTW is a source of
>> trouble on its own as you noticed.
>
> What trouble in patch 1 do you mean? I may miss something.
>
> I agree that patch 1 is not necessary if we decide to use sysdata or rework
> root bus scanning to move domain to host bridge. Nevertheless, patch 1 is
> still a cleanup IMO.

In this case, getting the domain should be trivial since the ACPI
companion on parent is already set, this should work

int acpi_pci_bus_domain_nr(struct device *parent)
{
        struct acpi_device *acpi_dev = to_acpi_device(parent);
        struct acpi_pci_root *root = acpi_dev->driver_data;

        return root->segment;
}

Or am I missing something here?

JC.