[PATCH 3/6] PCI: restore memory decoding after reallocation

Stewart Hildebrand
2024-07-09T13:36:43Z

Currently, the PCI subsystem unconditionally clears the memory decoding
bit of devices with resource alignment specified. Unfortunately, some
drivers assume memory decoding was enabled by firmware. Restore the
memory decoding bit after the resource has been reallocated.

Signed-off-by: Stewart Hildebrand <stewart.hildebrand@amd.com>
---
Relevant prior discussion at [1]

[1] https://lore.kernel.org/linux-pci/20160906165652.GE1214@localhost/
---
drivers/pci/pci.c | 1 +
drivers/pci/setup-bus.c | 25 +++++++++++++++++++++++++
include/linux/pci.h | 2 ++
3 files changed, 28 insertions(+)

diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index f017e7a8f028..7953e75b9129 100644
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -6633,6 +6633,7 @@ void pci_reassigndev_resource_alignment(struct pci_dev *dev)

pci_read_config_word(dev, PCI_COMMAND, &command);
if (command & PCI_COMMAND_MEMORY) {
+ dev->dev_flags |= PCI_DEV_FLAGS_MEMORY_ENABLE;
command &= ~PCI_COMMAND_MEMORY;
pci_write_config_word(dev, PCI_COMMAND, command);
}
diff --git a/drivers/pci/setup-bus.c b/drivers/pci/setup-bus.c
index ab7510ce6917..6847b251e19a 100644
--- a/drivers/pci/setup-bus.c
+++ b/drivers/pci/setup-bus.c
@@ -2131,6 +2131,29 @@ pci_root_bus_distribute_available_resources(struct pci_bus *bus,
}
}

+static void restore_memory_decoding(struct pci_bus *bus)
+{
+ struct pci_dev *dev;
+
+ list_for_each_entry(dev, &bus->devices, bus_list) {
+ struct pci_bus *b;
+
+ if (dev->dev_flags & PCI_DEV_FLAGS_MEMORY_ENABLE) {
+ u16 command;
+
+ pci_read_config_word(dev, PCI_COMMAND, &command);
+ command |= PCI_COMMAND_MEMORY;
+ pci_write_config_word(dev, PCI_COMMAND, command);
+ }
+
+ b = dev->subordinate;
+ if (!b)
+ continue;
+
+ restore_memory_decoding(b);
+ }
+}
+
/*
* First try will not touch PCI bridge res.
* Second and later try will clear small leaf bridge res.
@@ -2229,6 +2252,8 @@ void pci_assign_unassigned_root_bus_resources(struct pci_bus *bus)
goto again;

dump:
+ restore_memory_decoding(bus);
+
/* Dump the resource on buses */
pci_bus_dump_resources(bus);
}
diff --git a/include/linux/pci.h b/include/linux/pci.h
index e83ac93a4dcb..cb5df4c6a999 100644
--- a/include/linux/pci.h
+++ b/include/linux/pci.h
@@ -245,6 +245,8 @@ enum pci_dev_flags {
PCI_DEV_FLAGS_NO_RELAXED_ORDERING = (__force pci_dev_flags_t) (1 << 11),
/* Device does honor MSI masking despite saying otherwise */
PCI_DEV_FLAGS_HAS_MSI_MASKING = (__force pci_dev_flags_t) (1 << 12),
+ /* Firmware enabled memory decoding, to be restored if BAR is updated */
+ PCI_DEV_FLAGS_MEMORY_ENABLE = (__force pci_dev_flags_t) (1 << 13),
};

enum pci_irq_reroute_variant {
--
2.45.2