[PATCHv4 2/3] pci: allow all bus devices to use the same slot

[Keith Busch <kbusch@meta.com>]

From: Keith Busch <kbusch@kernel.org>

A pcie hotplug slot applies to the entire subordinate bus. Thus, pciehp
only allocates a single hotplug_slot for the bridge to that bus. The pci
slot, though, would only match to functions on device 0, meaning all
device beyond that are not matched to any slot even though they share
it. A slot reset will break all the missing devices because the handling
skips them.

Allow a slot to be created to claim all devices on a bus, not just a
matching device. This is done by introducing a sentinel value, named
PCI_SLOT_ALL_DEVICES, which then has the pci slot match to any device on
the bus. This fixes slot resets for pciehp.

Since 0xff already has special meaning, the chosen value for this new
feature is 0xfe. This will not clash with any actual slot number since
they are limited to 5 bits.

Reviewed-by: Dan Williams <dan.j.williams@intel.com>
Signed-off-by: Keith Busch <kbusch@kernel.org>
---
 drivers/pci/hotplug/pciehp_core.c |  3 ++-
 drivers/pci/slot.c                | 27 +++++++++++++++++++++++----
 include/linux/pci.h               |  8 +++++++-
 3 files changed, 32 insertions(+), 6 deletions(-)

diff --git a/drivers/pci/hotplug/pciehp_core.c b/drivers/pci/hotplug/pciehp_core.c
index f59baa9129709..d80346d567049 100644
--- a/drivers/pci/hotplug/pciehp_core.c
+++ b/drivers/pci/hotplug/pciehp_core.c
@@ -79,7 +79,8 @@ static int init_slot(struct controller *ctrl)
 	snprintf(name, SLOT_NAME_SIZE, "%u", PSN(ctrl));
 
 	retval = pci_hp_initialize(&ctrl->hotplug_slot,
-				   ctrl->pcie->port->subordinate, 0, name);
+				   ctrl->pcie->port->subordinate,
+				   PCI_SLOT_ALL_DEVICES, name);
 	if (retval) {
 		ctrl_err(ctrl, "pci_hp_initialize failed: error %d\n", retval);
 		kfree(ops);
diff --git a/drivers/pci/slot.c b/drivers/pci/slot.c
index 50fb3eb595fe6..bf6f265454a84 100644
--- a/drivers/pci/slot.c
+++ b/drivers/pci/slot.c
@@ -42,6 +42,15 @@ static ssize_t address_read_file(struct pci_slot *slot, char *buf)
 				  pci_domain_nr(slot->bus),
 				  slot->bus->number);
 
+	/*
+	 * Preserve legacy ABI expectations that hotplug drivers that manage
+	 * multiple devices per slot emit 0 for the device number.
+	 */
+	if (slot->number == PCI_SLOT_ALL_DEVICES)
+		return sysfs_emit(buf, "%04x:%02x:00\n",
+				  pci_domain_nr(slot->bus),
+				  slot->bus->number);
+
 	return sysfs_emit(buf, "%04x:%02x:%02x\n",
 			  pci_domain_nr(slot->bus),
 			  slot->bus->number,
@@ -73,7 +82,8 @@ static void pci_slot_release(struct kobject *kobj)
 
 	down_read(&pci_bus_sem);
 	list_for_each_entry(dev, &slot->bus->devices, bus_list)
-		if (PCI_SLOT(dev->devfn) == slot->number)
+		if (slot->number == PCI_SLOT_ALL_DEVICES ||
+		    PCI_SLOT(dev->devfn) == slot->number)
 			dev->slot = NULL;
 	up_read(&pci_bus_sem);
 
@@ -166,7 +176,8 @@ void pci_dev_assign_slot(struct pci_dev *dev)
 
 	mutex_lock(&pci_slot_mutex);
 	list_for_each_entry(slot, &dev->bus->slots, list)
-		if (PCI_SLOT(dev->devfn) == slot->number)
+		if (slot->number == PCI_SLOT_ALL_DEVICES ||
+		    PCI_SLOT(dev->devfn) == slot->number)
 			dev->slot = slot;
 	mutex_unlock(&pci_slot_mutex);
 }
@@ -188,7 +199,7 @@ static struct pci_slot *get_slot(struct pci_bus *parent, int slot_nr)
 /**
  * pci_create_slot - create or increment refcount for physical PCI slot
  * @parent: struct pci_bus of parent bridge
- * @slot_nr: PCI_SLOT(pci_dev->devfn) or -1 for placeholder
+ * @slot_nr: PCI_SLOT(pci_dev->devfn), -1 for placeholder, or PCI_SLOT_ALL_DEVICES
  * @name: user visible string presented in /sys/bus/pci/slots/<name>
  * @hotplug: set if caller is hotplug driver, NULL otherwise
  *
@@ -222,6 +233,13 @@ static struct pci_slot *get_slot(struct pci_bus *parent, int slot_nr)
  * consist solely of a dddd:bb tuple, where dddd is the PCI domain of the
  * %struct pci_bus and bb is the bus number. In other words, the devfn of
  * the 'placeholder' slot will not be displayed.
+ *
+ * Bus-wide slots:
+ * For PCIe hotplug, the physical slot encompasses the entire subordinate
+ * bus, not just a single device number. Pass @slot_nr == PCI_SLOT_ALL_DEVICES
+ * to create a slot that matches all devices on the bus. Unlike placeholder
+ * slots, bus-wide slots go through normal slot lookup and reuse existing
+ * slots if present.
  */
 struct pci_slot *pci_create_slot(struct pci_bus *parent, int slot_nr,
 				 const char *name,
@@ -285,7 +303,8 @@ struct pci_slot *pci_create_slot(struct pci_bus *parent, int slot_nr,
 
 	down_read(&pci_bus_sem);
 	list_for_each_entry(dev, &parent->devices, bus_list)
-		if (PCI_SLOT(dev->devfn) == slot_nr)
+		if (slot_nr == PCI_SLOT_ALL_DEVICES ||
+		    PCI_SLOT(dev->devfn) == slot_nr)
 			dev->slot = slot;
 	up_read(&pci_bus_sem);
 
diff --git a/include/linux/pci.h b/include/linux/pci.h
index edf792a79193f..7073519bcc1ad 100644
--- a/include/linux/pci.h
+++ b/include/linux/pci.h
@@ -72,12 +72,18 @@
 /* return bus from PCI devid = ((u16)bus_number) << 8) | devfn */
 #define PCI_BUS_NUM(x) (((x) >> 8) & 0xff)
 
+/*
+ * PCI_SLOT_ALL_DEVICES indicates a slot that covers all devices on the bus.
+ * Used for PCIe hotplug where the physical slot is the entire subordinate bus.
+ */
+#define PCI_SLOT_ALL_DEVICES	0xfe
+
 /* pci_slot represents a physical slot */
 struct pci_slot {
 	struct pci_bus		*bus;		/* Bus this slot is on */
 	struct list_head	list;		/* Node in list of slots */
 	struct hotplug_slot	*hotplug;	/* Hotplug info (move here) */
-	unsigned char		number;		/* PCI_SLOT(pci_dev->devfn) */
+	unsigned char		number;		/* Device nr, or PCI_SLOT_ALL_DEVICES */
 	struct kobject		kobj;
 };
 
-- 
2.47.3