[PATCH v7-incomplete 2/3] PCI: of: Add of_pci_preserve_config() for per-host bridge support

Bjorn Helgaas
2024-04-21T19:09:31Z

From: Bjorn Helgaas <bhelgaas@google.com>

Add of_pci_preserve_config() to look for the "linux,pci-probe-only"
property under a specified node. If it's not found there, look under
"of_chosen" in addition.

If the caller didn't specify a node, look under "of_chosen".

With a future patch, this will support "linux,pci-probe-only" on a per host
bridge basis based on the presence of the property in the respective PCI
host bridge DT node.

Implement of_pci_check_probe_only() using of_pci_preserve_config().
---
drivers/pci/of.c | 60 +++++++++++++++++++++++++++++++++++++----------
drivers/pci/pci.h | 7 ++++++
2 files changed, 54 insertions(+), 13 deletions(-)

diff --git a/drivers/pci/of.c b/drivers/pci/of.c
index 51e3dd0ea5ab..d21c0bed36f3 100644
--- a/drivers/pci/of.c
+++ b/drivers/pci/of.c
@@ -233,28 +233,62 @@ int of_get_pci_domain_nr(struct device_node *node)
}
EXPORT_SYMBOL_GPL(of_get_pci_domain_nr);

+/**
+ * of_pci_preserve_config - Return true if the boot configuration needs to
+ * be preserved
+ * @node: Device tree node.
+ *
+ * This function looks for "linux,pci-probe-only" property for a given
+ * PCI controller's node and returns true if found. It will also look in the
+ * chosen node if the property is not found in the given controller's node.
+ * Having this property ensures that the kernel doesn't reconfigure the
+ * BARs and bridge windows that are already done by the platform firmware.
+ *
+ * Return: true if the property exists false otherwise.
+ */
+bool of_pci_preserve_config(struct device_node *node)
+{
+ u32 val = 0;
+ int ret;
+
+ if (!node) {
+ pr_warn("device node is NULL, trying with of_chosen\n");
+ node = of_chosen;
+ }
+
+retry:
+ ret = of_property_read_u32(node, "linux,pci-probe-only", &val);
+ if (ret) {
+ if (ret == -ENODATA || ret == -EOVERFLOW) {
+ pr_warn("Incorrect value for linux,pci-probe-only in %pOF, ignoring\n",
+ node);
+ return false;
+ }
+ if (ret == -EINVAL) {
+ if (node == of_chosen)
+ return false;
+
+ node = of_chosen;
+ goto retry;
+ }
+ }
+
+ if (val)
+ return true;
+ else
+ return false;
+}
+
/**
* of_pci_check_probe_only - Setup probe only mode if linux,pci-probe-only
* is present and valid
*/
void of_pci_check_probe_only(void)
{
- u32 val;
- int ret;
-
- ret = of_property_read_u32(of_chosen, "linux,pci-probe-only", &val);
- if (ret) {
- if (ret == -ENODATA || ret == -EOVERFLOW)
- pr_warn("linux,pci-probe-only without valid value, ignoring\n");
- return;
- }
-
- if (val)
+ if (of_pci_preserve_config(of_chosen))
pci_add_flags(PCI_PROBE_ONLY);
else
pci_clear_flags(PCI_PROBE_ONLY);
-
- pr_info("PROBE_ONLY %s\n", val ? "enabled" : "disabled");
}
EXPORT_SYMBOL_GPL(of_pci_check_probe_only);

diff --git a/drivers/pci/pci.h b/drivers/pci/pci.h
index 180d3907b543..feedbedd65df 100644
--- a/drivers/pci/pci.h
+++ b/drivers/pci/pci.h
@@ -650,6 +650,7 @@ int of_pci_get_max_link_speed(struct device_node *node);
u32 of_pci_get_slot_power_limit(struct device_node *node,
u8 *slot_power_limit_value,
u8 *slot_power_limit_scale);
+bool of_pci_preserve_config(struct device_node *node);
int pci_set_of_node(struct pci_dev *dev);
void pci_release_of_node(struct pci_dev *dev);
void pci_set_bus_of_node(struct pci_bus *bus);
@@ -688,6 +689,12 @@ of_pci_get_slot_power_limit(struct device_node *node,
return 0;
}

+static inline bool
+of_pci_preserve_config(struct device_node *node)
+{
+ return false;
+}
+
static inline int pci_set_of_node(struct pci_dev *dev) { return 0; }
static inline void pci_release_of_node(struct pci_dev *dev) { }
static inline void pci_set_bus_of_node(struct pci_bus *bus) { }
--
2.34.1