External email: Use caution opening links or attachmentsI'll change it in the next patch.
On Thu, Feb 22, 2024 at 06:11:10PM +0530, Vidya Sagar wrote:
Add support for preserving the boot configuration done by theI don't like the "check_probe_only" name because it's a boolean
platform firmware per host bridge basis, based on the presence of
'linux,pci-probe-only' property in the respective PCIe host bridge
device-tree node. It also unifies the ACPI and DT based boot flows
in this regard.
+/**
+ * of_pci_bridge_check_probe_only - Return true if the boot configuration
+ * needs to be preserved
function but the name doesn't tell me what a true/false return value
means. Something like "preserve_resources" would be better. If you
want "probe_only", even removing the "check" would help.
Agree and I'll address it in the next patch.+ * @node: Device tree node with the domain information.This is generic PCI, not PCIe-specific (also in commit log and comment
+ *
+ * This function looks for "linux,pci-probe-only" property for a given
+ * PCIe controller's node and returns true if found. Having this property
+ * for a PCIe controller ensures that the kernel doesn't re-enumerate and
+ * reconfigure the BAR resources that are already done by the platform firmware.
below).
I think "enumeration" specifically refers to discovering what devices
are present, and the kernel always does that, so drop that part.
Reconfiguring BARs and bridge windows is what we want to prevent.
On a second through, I think it is not required to be exported.+ * NOTE: The scope of "linux,pci-probe-only" defined within a PCIe bridge deviceWhy does this need to be exported for modules and exposed via
+ * is limited to the hierarchy under that particular bridge device. whereas
+ * the scope of "linux,pci-probe-only" defined within chosen node is
+ * system wide.
+ *
+ * Return: true if the property exists false otherwise.
+ */
+bool of_pci_bridge_check_probe_only(struct device_node *node)
+{
+ return of_property_read_bool(node, "linux,pci-probe-only");
+}
+EXPORT_SYMBOL_GPL(of_pci_bridge_check_probe_only);
include/linux/pci.h?
Honestly, I couldn't find a clear way to differentiate between an ACPI based+static void pci_check_config_preserve(struct pci_host_bridge *host_bridge)Checking &host_bridge->dev doesn't seem like the right way to
+{
+ if (&host_bridge->dev) {
determine whether this is an ACPI host bridge.
+ union acpi_object *obj;
+
+ /*
+ * Evaluate the "PCI Boot Configuration" _DSM Function. If it
+ * exists and returns 0, we must preserve any PCI resource
+ * assignments made by firmware for this host bridge.
+ */
+ obj = acpi_evaluate_dsm(ACPI_HANDLE(&host_bridge->dev), &pci_acpi_dsm_guid, 1,
+ DSM_PCI_PRESERVE_BOOT_CONFIG, NULL);
+ if (obj && obj->type == ACPI_TYPE_INTEGER && obj->integer.value == 0)
+ host_bridge->preserve_config = 1;
+ ACPI_FREE(obj);
+ }