Re: [Patch v7 4/7] PCI/ACPI: Add interface acpi_pci_root_create()

[Tomasz Nowicki <tomasz.nowicki@linaro.org>]

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@arm.com>
>>> Tested-by: Tony Luck <tony.luck@intel.com>
>>> Signed-off-by: Jiang Liu <jiang.liu@linux.intel.com>
>>> Signed-off-by: Liu Jiang <jiang.liu@linux.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.

Thanks,
Tomasz