Re: [PATCH 2/2] PCI, ACPI, x86: update MMCFG information when hot-plugging PCI host bridges

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(2012/04/10 1:02), Jiang Liu wrote:
Hi Kenji,
	Thanks for your careful review and comments.

On 04/09/2012 07:43 PM, Kenji Kaneshige wrote:
Your patch looks good to me.

I have some comments.

(2012/04/09 2:12), Jiang Liu wrote:
This patch enhances pci_root driver to update MMCFG information when
hot-plugging PCI root bridges on x86 platforms.


Do you have the patch that can be applied to Bjorn's pci tree?

<snip.>
Will try to generate a version against Bjorn's version. Could you please tell
me the exact git link for that? I haven't pull from Bjorn's tree yet.

As you may know, it was announced _today_ (sorry:).

http://www.spinics.net/lists/linux-pci/msg14626.html



+int arch_acpi_pci_root_add(struct acpi_pci_root *root)
+{
+	int result = 0;
+	acpi_status status;
+	unsigned long long base_addr;
+	struct pci_mmcfg_region *cfg;
+
+	/*
+	 * Try to insert MMCFG information for host bridges with _CBA method
+	 */
+	status = acpi_evaluate_integer(root->device->handle, METHOD_NAME__CBA,
+				       NULL,&base_addr);
+	if (ACPI_SUCCESS(status)) {
+		result = pci_mmconfig_insert(root->segment,
+					     root->secondary.start,
+					     root->secondary.end,
+					     base_addr);
+		/*
+		 * MMCFG information for hot-pluggable host bridges may have
+		 * already been added by __pci_mmcfg_init();
+		 */
+		if (result == -EEXIST)
+			result = 0;

Just for confirmation.
 From my interpretation of PCI firmware spec, MCFG doesn't have any entry
for hot-pluggable hostbridge. So I assume this is for the machine that
is not compliant to the spec. Is my understanding same as yours?

<snip.>
You are right, it's defined to that way in PCI FW Spec 3.1.
Here I have some concerns about the PCI buses to host all Ubox components
on Intel NHM/WSM/SNB/IVB processors. BIOS people are prone to declare
MMCFG information for those host bridges by MCFG table instead of _CBA method,
though those host bridge will disappear after hot-removing a physical processor.

Ok, thank you for clarification.



   static int __devinit acpi_pci_root_add(struct acpi_device *device)
   {
   	unsigned long long segment, bus;
@@ -504,6 +514,14 @@ static int __devinit acpi_pci_root_add(struct acpi_device *device)
   	strcpy(acpi_device_class(device), ACPI_PCI_ROOT_CLASS);
   	device->driver_data = root;

+	if (arch_acpi_pci_root_add(root)) {
+		printk(KERN_ERR PREFIX
+			"can't add MMCFG information for Bus %04x:%02x\n",
+			root->segment, (unsigned int)root->secondary.start);

Additional comment.

This printk message looks strange because arch_acpi_pci_root_add()
is not a mmconfig specific function. So I think this message
should be moved to arch specific code (arch_acpi_pci_root_add()).

+		result = -ENODEV;
+		goto out_free;
+	}

Desn't this break the system that doesn't support MMCONFIG?

In my understanding, arch_acpi_pci_root_add() returns -ENODEV if
mmconfig information is found neither in MCFG table nor _CBA. And
pci root bridge initialization seems to fail arch_acpi_pci_root_add()
returns non-zero value.
Good catch, will add following code into arch_acpi_pci_root_add() and
arch_acpi_pci_root_remove() to solve this issue.
---
         /* MMCONFIG disabled */
         if ((pci_probe&  PCI_PROBE_MMCONF) == 0)
                 return 0;
---

My understanding is that PCI_PROBE_MMCONF is set even if the system
doesn't have MCFG table. So I don't think this solves the issue. I
guess this is what Yinghai pointed out on your V2 patch [6/6].

Additionally, I think there is a remaining issue even if we change
this check like below.

	if (!!(pci_probe & PCI_PROBE_MASK & ~PCI_PROBE_MMCONF))
        	return 0;

I think this check has an assumption that system has at least one
MCFG table entry and it has been initialized before
acpi_pci_root_add() is called. I think this doesn't work on the
system that doesn't have MCFG and all the pci root bridge have
_CBA (that is, all host bridges are hot-pluggable and BIOS is
implemented in the way PCI FW spec defines). As a result, MMCONFIG
would never be enabled on such systems. Could you double check this?

Regards,
Kenji Kaneshige
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