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

[Liviu Dudau]

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@xxxxxxx>
> >>>Tested-by: Tony Luck <tony.luck@xxxxxxxxx>
> >>>Signed-off-by: Jiang Liu <jiang.liu@xxxxxxxxxxxxxxx>
> >>>Signed-off-by: Liu Jiang <jiang.liu@xxxxxxxxxxxxxxx>
> >>>---
> >>>  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 thought so. What about adding code to pci_bus_assign_domain_nr() to get the
segment nr from MCFG table? I know the function looks scary and the comments
don't seem to acknowledge that use_dt_domain static variable has actually 3
possible values (-1, 0, 1) but you can use -1 to mean "try ACPI segment nr
first" (just a suggestion, you or others might have a better idea).

Best regards,
Liviu

> 
> Thanks,
> Tomasz
> 

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