On Thu, Jan 21, 2016 at 07:38:51PM +0100, Tomasz Nowicki wrote:

[...]

quoted

I think you can reshuffle a bit the code to make it easier to follow.

How about this ? (on top of mainline, I just compiled it do not
take it verbatim):

-- >8 --

diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index d1a7105..467a316 100644
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c

@@ -7,6 +7,7 @@
  *	Copyright 1997 -- 2000 Martin Mares <mj@ucw.cz>
  */

+#include <linux/acpi.h>
 #include <linux/kernel.h>
 #include <linux/delay.h>
 #include <linux/init.h>

@@ -4769,7 +4770,27 @@ int pci_get_new_domain_nr(void)
 }

 #ifdef CONFIG_PCI_DOMAINS_GENERIC
-void pci_bus_assign_domain_nr(struct pci_bus *bus, struct device *parent)
+/* Feel free to add this to drivers/acpi as a helper */
+#ifdef CONFIG_ACPI
+int pci_bus_acpi_domain_nr(struct device *parent)
+{
+	struct acpi_device *acpi_dev = to_acpi_device(parent);
+	unsigned long long segment = 0;
+	acpi_status status;
+
+	status = acpi_evaluate_integer(acpi_dev->handle,
+				       METHOD_NAME__SEG, NULL,
+				       &segment);
+	if (ACPI_FAILURE(status) && status != AE_NOT_FOUND)
+		dev_err(&acpi_dev->dev,  "can't evaluate _SEG\n");
+
+	return segment;
+}
+#else
+int pci_bus_acpi_domain_nr(struct device *parent) { return -1; }
+#endif
+
+int pci_bus_of_domain_nr(struct device *parent)
 {
 	static int use_dt_domains = -1;
 	int domain = of_get_pci_domain_nr(parent->of_node);

@@ -4811,7 +4832,13 @@ void pci_bus_assign_domain_nr(struct pci_bus *bus, struct device *parent)
 		domain = -1;
 	}

-	bus->domain_nr = domain;
+	return domain;
+}
+
+void pci_bus_assign_domain_nr(struct pci_bus *bus, struct device *parent)
+{
+	bus->domain_nr = acpi_disabled ? pci_bus_of_domain_nr(parent) :
+					 pci_bus_acpi_domain_nr(parent);
 }
 #endif
 #endif

It looks nice, I will integrate your patch. Thanks!

While at it, as I mentioned, please move the ACPI helper function to
drivers/acpi, thanks.

Lorenzo