On Fri, Aug 20, 2021 at 7:16 PM Jon Derrick [off-list ref] wrote:

quoted

On Aug 20, 2021, at 11:12 AM, Rafael J. Wysocki [off-list ref] wrote:

From: Rafael J. Wysocki [off-list ref]

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 <redacted>
Tested-by: Wendy Wang <redacted>
---
drivers/pci/controller/vmd.c |   48 ++++++++++++++++++++++++++
drivers/pci/host-bridge.c    |    1
drivers/pci/pci-acpi.c       |   78 +++++++++++++++++++++++++++++++++++++++++++
include/linux/pci-acpi.h     |    3 +
4 files changed, 130 insertions(+)

Index: linux-pm/drivers/pci/controller/vmd.c
===================================================================

--- linux-pm.orig/drivers/pci/controller/vmd.c
+++ linux-pm/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 +448,49 @@ 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;

Can we use is_vmd(pci_dev->bus)?

Sure.

quoted

+
+    bridge = pci_find_host_bridge(pci_dev->bus);
+    busnr = pci_dev->bus->number - bridge->bus->number;

This is just the bus->number - vmd->busn_start, correct?

Yes, it is, but vmd is not known here AFAICS.

quoted

+    addr = (busnr << 24) | ((u32)pci_dev->devfn << 16) | 0x8000FFFFU;

So the descriptor assumes busnr < 128 and requires an appropriately sized CFGBAR. Client is typically limited to 32 sub device buses but I’m not certain if enterprise will ever need > 128 (256 is allowed).

It actually assumes busnr < 32.

Well, that's what the formula is, but I need to return NULL if > 31.

I'm not expecting the ACPI objects to be present on servers even.

quoted

+
+    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 +791,8 @@ static int vmd_enable_domain(struct vmd_
  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 +806,8 @@ static int vmd_enable_domain(struct vmd_

  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;

Index: linux-pm/drivers/pci/host-bridge.c
===================================================================

--- linux-pm.orig/drivers/pci/host-bridge.c
+++ linux-pm/drivers/pci/host-bridge.c

@@ -23,6 +23,7 @@ struct pci_host_bridge *pci_find_host_br

  return to_pci_host_bridge(root_bus->bridge);

}
+EXPORT_SYMBOL_GPL(pci_find_host_bridge);

struct device *pci_get_host_bridge_device(struct pci_dev *dev)
{
Index: linux-pm/drivers/pci/pci-acpi.c
===================================================================

--- linux-pm.orig/drivers/pci/pci-acpi.c
+++ linux-pm/drivers/pci/pci-acpi.c

@@ -1159,6 +1159,72 @@ void acpi_pci_remove_bus(struct pci_bus

}

/* ACPI bus type */
+
+
+DEFINE_STATIC_KEY_FALSE(pci_acpi_companion_lookup_key);
+static DEFINE_MUTEX(pci_acpi_companion_lookup_mtx);
+static struct acpi_device *(*pci_acpi_find_companion_hook)(struct pci_dev *);

Wouldn’t a hook list be a better structure? Or is that too heavy handed for the purpose?

It might, but would that list ever contain more than 1 entry?  If not,
then it would be a redundant complication IMO.

quoted

+
+/**
+ * pci_acpi_set_companion_lookup_hook - Set ACPI companion lookup callback.
+ * @func: ACPI companion lookup callback pointer or NULL.
+ *
+ * Set a special ACPI companion lookup callback for PCI devices whose companion
+ * objects in the ACPI namespace have _ADR with non-standard bus-device-function
+ * encodings.
+ *
+ * Return 0 on success or a negative error code on failure (in which case no
+ * changes are made).
+ *
+ * The caller is responsible for the appropriate ordering of the invocations of
+ * this function with respect to the enumeration of the PCI devices needing the
+ * callback installed by it.
+ */
+int pci_acpi_set_companion_lookup_hook(struct acpi_device *(*func)(struct pci_dev *))
+{
+    int ret;
+
+    if (!func)
+        return -EINVAL;
+
+    mutex_lock(&pci_acpi_companion_lookup_mtx);
+
+    if (pci_acpi_find_companion_hook) {
+        ret = -EBUSY;
+    } else {
+        pci_acpi_find_companion_hook = func;
+        static_branch_enable(&pci_acpi_companion_lookup_key);
+        ret = 0;
+    }
+
+    mutex_unlock(&pci_acpi_companion_lookup_mtx);
+
+    return ret;
+}
+EXPORT_SYMBOL_GPL(pci_acpi_set_companion_lookup_hook);
+
+/**
+ * pci_acpi_clear_companion_lookup_hook - Clear ACPI companion lookup callback.
+ *
+ * Clear the special ACPI companion lookup callback previously set by
+ * pci_acpi_set_companion_lookup_hook().  Block until the last running instance
+ * of the callback returns before clearing it.
+ *
+ * The caller is responsible for the appropriate ordering of the invocations of
+ * this function with respect to the enumeration of the PCI devices needing the
+ * callback cleared by it.
+ */
+void pci_acpi_clear_companion_lookup_hook(void)
+{
+    mutex_lock(&pci_acpi_companion_lookup_mtx);
+
+    pci_acpi_find_companion_hook = NULL;
+    static_branch_disable(&pci_acpi_companion_lookup_key);
+
+    mutex_unlock(&pci_acpi_companion_lookup_mtx);
+}
+EXPORT_SYMBOL_GPL(pci_acpi_clear_companion_lookup_hook);
+
static struct acpi_device *acpi_pci_find_companion(struct device *dev)
{
  struct pci_dev *pci_dev = to_pci_dev(dev);

@@ -1166,6 +1232,18 @@ static struct acpi_device *acpi_pci_find
  bool check_children;
  u64 addr;

+    if (static_branch_unlikely(&pci_acpi_companion_lookup_key)) {
+        mutex_lock(&pci_acpi_companion_lookup_mtx);
+
+        adev = pci_acpi_find_companion_hook ?
+            pci_acpi_find_companion_hook(pci_dev) : NULL;
+
+        mutex_unlock(&pci_acpi_companion_lookup_mtx);
+
+        if (adev)
+            return adev;
+    }
+
  check_children = pci_is_bridge(pci_dev);
  /* Please ref to ACPI spec for the syntax of _ADR */
  addr = (PCI_SLOT(pci_dev->devfn) << 16) | PCI_FUNC(pci_dev->devfn);

Index: linux-pm/include/linux/pci-acpi.h
===================================================================

--- linux-pm.orig/include/linux/pci-acpi.h
+++ linux-pm/include/linux/pci-acpi.h

@@ -122,6 +122,9 @@ static inline void pci_acpi_add_edr_noti

static inline void pci_acpi_remove_edr_notifier(struct pci_dev *pdev) { }
#endif /* CONFIG_PCIE_EDR */

+int pci_acpi_set_companion_lookup_hook(struct acpi_device *(*func)(struct pci_dev *));
+void pci_acpi_clear_companion_lookup_hook(void);
+
#else    /* CONFIG_ACPI */
static inline void acpi_pci_add_bus(struct pci_bus *bus) { }
static inline void acpi_pci_remove_bus(struct pci_bus *bus) { }