Hi Tomasz,

On Wed, Jan 13, 2016 at 02:20:59PM +0100, Tomasz Nowicki wrote:

[...]

quoted

@@ -4796,14 +4797,34 @@ void pci_bus_assign_domain_nr(struct pci_bus *bus, struct device *parent)
  	 * API and update the use_dt_domains value to keep track of method we
  	 * are using to assign domain numbers (use_dt_domains = 0).
  	 *
+	 * IF ACPI, we expect non-DT method (use_dt_domains == -1)
+	 * and call _SEG method for corresponding host bridge device.
+	 * If _SEG method does not exist, following ACPI spec (6.5.6)
+	 * all PCI buses belong to domain 0.
+	 *
  	 * All other combinations imply we have a platform that is trying
-	 * to mix domain numbers obtained from DT and pci_get_new_domain_nr(),
-	 * which is a recipe for domain mishandling and it is prevented by
-	 * invalidating the domain value (domain = -1) and printing a
-	 * corresponding error.
+	 * to mix domain numbers obtained from DT, ACPI and
+	 * pci_get_new_domain_nr(), which is a recipe for domain mishandling and
+	 * it is prevented by invalidating the domain value (domain = -1) and
+	 * printing a corresponding error.
  	 */
+
  	if (domain >= 0 && use_dt_domains) {
  		use_dt_domains = 1;
+#ifdef CONFIG_ACPI
+	} else if (!acpi_disabled && use_dt_domains == -1) {
+		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");
+
+		domain = segment;
+#endif

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