PCI: VMD: ACPI: Make ACPI companion lookup work for VMD bus

On some systems, in order to get to the deepest low-power state of
the platform (which may be necessary to save significant enough
amounts of energy while suspended to idle. for example), devices on
the PCI bus exposed by the VMD driver need to be power-managed via
ACPI.  However, the layout of the ACPI namespace below the VMD
controller device object does not reflect the layout of the PCI bus
under the VMD host bridge, so in order to identify the ACPI companion
objects for the devices on that bus, it is necessary to use a special
_ADR encoding on the ACPI side.  In other words, acpi_pci_find_companion()
does not work for these devices, so it needs to be amended with a
special lookup logic specific to the VMD bus.

Address this issue by allowing the VMD driver to temporarily install
an ACPI companion lookup hook containing the code matching the devices
on the VMD PCI bus with the corresponding objects in the ACPI
namespace.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: Jon Derrick <jonathan.derrick@intel.com>

1 files changed, 55 insertions, 0 deletions

diff --git a/drivers/pci/controller/vmd.c b/drivers/pci/controller/vmd.c
index e3fcdfec58b3..a5987e52700e 100644
--- a/drivers/pci/controller/vmd.c
+++ b/drivers/pci/controller/vmd.c
@@ -11,6 +11,7 @@
 #include <linux/module.h>
 #include <linux/msi.h>
 #include <linux/pci.h>
+#include <linux/pci-acpi.h>
 #include <linux/pci-ecam.h>
 #include <linux/srcu.h>
 #include <linux/rculist.h>
@@ -447,6 +448,56 @@ static struct pci_ops vmd_ops = {
 	.write		= vmd_pci_write,
 };
 
+#ifdef CONFIG_ACPI
+static struct acpi_device *vmd_acpi_find_companion(struct pci_dev *pci_dev)
+{
+	struct pci_host_bridge *bridge;
+	u32 busnr, addr;
+
+	if (pci_dev->bus->ops != &vmd_ops)
+		return NULL;
+
+	bridge = pci_find_host_bridge(pci_dev->bus);
+	busnr = pci_dev->bus->number - bridge->bus->number;
+	/*
+	 * The address computation below is only applicable to relative bus
+	 * numbers below 32.
+	 */
+	if (busnr > 31)
+		return NULL;
+
+	addr = (busnr << 24) | ((u32)pci_dev->devfn << 16) | 0x8000FFFFU;
+
+	dev_dbg(&pci_dev->dev, "Looking for ACPI companion (address 0x%x)\n",
+		addr);
+
+	return acpi_find_child_device(ACPI_COMPANION(bridge->dev.parent), addr,
+				      false);
+}
+
+static bool hook_installed;
+
+static void vmd_acpi_begin(void)
+{
+	if (pci_acpi_set_companion_lookup_hook(vmd_acpi_find_companion))
+		return;
+
+	hook_installed = true;
+}
+
+static void vmd_acpi_end(void)
+{
+	if (!hook_installed)
+		return;
+
+	pci_acpi_clear_companion_lookup_hook();
+	hook_installed = false;
+}
+#else
+static inline void vmd_acpi_begin(void) { }
+static inline void vmd_acpi_end(void) { }
+#endif /* CONFIG_ACPI */
+
 static void vmd_attach_resources(struct vmd_dev *vmd)
 {
 	vmd->dev->resource[VMD_MEMBAR1].child = &vmd->resources[1];
@@ -747,6 +798,8 @@ static int vmd_enable_domain(struct vmd_dev *vmd, unsigned long features)
 	if (vmd->irq_domain)
 		dev_set_msi_domain(&vmd->bus->dev, vmd->irq_domain);
 
+	vmd_acpi_begin();
+
 	pci_scan_child_bus(vmd->bus);
 	pci_assign_unassigned_bus_resources(vmd->bus);
 
@@ -760,6 +813,8 @@ static int vmd_enable_domain(struct vmd_dev *vmd, unsigned long features)
 
 	pci_bus_add_devices(vmd->bus);
 
+	vmd_acpi_end();
+
 	WARN(sysfs_create_link(&vmd->dev->dev.kobj, &vmd->bus->dev.kobj,
 			       "domain"), "Can't create symlink to domain\n");
 	return 0;