linux-kernel - Re: [Patch v7 4/7] PCI/ACPI: Add interface acpi_pci_root

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Date:	Wed, 21 Oct 2015 14:16:51 +0200
From:	Tomasz Nowicki <tomasz.nowicki@...aro.org>
To:	Lorenzo Pieralisi <lorenzo.pieralisi@....com>
Cc:	Liviu Dudau <Liviu.Dudau@....com>,
	Jiang Liu <jiang.liu@...ux.intel.com>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	"Rafael J . Wysocki" <rafael.j.wysocki@...el.com>,
	Marc Zyngier <marc.zyngier@....com>,
	Hanjun Guo <hanjun.guo@...aro.org>, linux-acpi@...r.kernel.org,
	linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
	x86@...nel.org
Subject: Re: [Patch v7 4/7] PCI/ACPI: Add interface acpi_pci_root_create()

On 21.10.2015 13:42, Lorenzo Pieralisi wrote:
> On Wed, Oct 21, 2015 at 01:27:33PM +0200, Tomasz Nowicki wrote:
>> On 21.10.2015 13:02, Liviu Dudau wrote:
>>> On Wed, Oct 21, 2015 at 11:57:53AM +0200, Tomasz Nowicki wrote:
>>>> On 14.10.2015 08:29, Jiang Liu wrote:
>>>>> Introduce common interface acpi_pci_root_create() and related data
>>>>> structures to create PCI root bus for ACPI PCI host bridges. It will
>>>>> be used to kill duplicated arch specific code for IA64 and x86. It may
>>>>> also help ARM64 in future.
>>>>>
>>>>> Reviewed-by: Lorenzo Pieralisi <lorenzo.pieralisi@....com>
>>>>> Tested-by: Tony Luck <tony.luck@...el.com>
>>>>> Signed-off-by: Jiang Liu <jiang.liu@...ux.intel.com>
>>>>> Signed-off-by: Liu Jiang <jiang.liu@...ux.intel.com>
>>>>> ---
>>>>>   drivers/acpi/pci_root.c  |  204 ++++++++++++++++++++++++++++++++++++++++++++++
>>>>>   include/linux/pci-acpi.h |   24 ++++++
>>>>>   2 files changed, 228 insertions(+)
>>>>>
>>>>
>>>> [...]
>>>>
>>>>> +
>>>>> +struct pci_bus *acpi_pci_root_create(struct acpi_pci_root *root,
>>>>> +				     struct acpi_pci_root_ops *ops,
>>>>> +				     struct acpi_pci_root_info *info,
>>>>> +				     void *sysdata)
>>>>> +{
>>>>> +	int ret, busnum = root->secondary.start;
>>>>> +	struct acpi_device *device = root->device;
>>>>> +	int node = acpi_get_node(device->handle);
>>>>> +	struct pci_bus *bus;
>>>>> +
>>>>> +	info->root = root;
>>>>> +	info->bridge = device;
>>>>> +	info->ops = ops;
>>>>> +	INIT_LIST_HEAD(&info->resources);
>>>>> +	snprintf(info->name, sizeof(info->name), "PCI Bus %04x:%02x",
>>>>> +		 root->segment, busnum);
>>>>> +
>>>>> +	if (ops->init_info && ops->init_info(info))
>>>>> +		goto out_release_info;
>>>>> +	if (ops->prepare_resources)
>>>>> +		ret = ops->prepare_resources(info);
>>>>> +	else
>>>>> +		ret = acpi_pci_probe_root_resources(info);
>>>>> +	if (ret < 0)
>>>>> +		goto out_release_info;
>>>>> +
>>>>> +	pci_acpi_root_add_resources(info);
>>>>> +	pci_add_resource(&info->resources, &root->secondary);
>>>>> +	bus = pci_create_root_bus(NULL, busnum, ops->pci_ops,
>>>>> +				  sysdata, &info->resources);
>>>>
>>>> Thank a lot for this cleanup!!
>>>>
>>>> I recall you already considered passing segment (domain nr) to
>>>> pci_create_root_bus, right? Can you please remind me why we gave up on this?
>>>>
>>>> I am asking because currently I can not find the way to retrieve domain
>>>> number from pci_bus_assign_domain_nr (for those platforms which choose
>>>> PCI_DOMAINS_GENERIC and want to use segment nr from MCFG table) which is the
>>>> part of pci_create_root_bus.
>>>
>>> Not sure I fully understand your question, but pci_bus_assign_domain_nr() will
>>> put the assigned domain number in bus->domain_nr if you chose PCI_DOMAINS_GENERIC.
>>> Do you want to override that value with the segment nr from MCFG?
>>>
>>
>> Let me give ACPI ARM64 example:
>>
>> 1. We parse MCFG table and get segment nr assigned to root bridge
>> 2. Then PCI host bridge calls acpi_pci_root_create ->
>> pci_create_root_bus -> pci_bus_assign_domain_nr
>> 3. At this point we cannot get segment nr for ACPI
>>
>> So I would like to assign MCFG segment nr to bus->domain_nr being in
>> pci_bus_assign_domain_nr giving we have scenario above.
>
> I do not understand what you mean by "assign MCFG segment" here, please
> explain. The MCFG segment group number is used to look-up the configuration
> space for a given host bridge, not to assign a domain number to it.
>
> The domain_nr above is the value returned by the _SEG object for the host
> bridge device.

If I read the code correctly, MCFG region assigned to PCI host bridge X 
should have the same value for its segment field and corresponding _SEG 
object. Anyway, you are right, the MCFG segment group number should be 
used to look-up the configuration space and _SEG object to retrieve 
domain nr.

To evaluate _SEG object being in pci_bus_assign_domain_nr we still miss 
there the PCI host bridge device. So I should change my previous 
question, can we pass down the PCI host bridge device to be able to call 
_SEG object being in pci_bus_assign_domain_nr?

Thanks,
Tomasz
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