@@ -344,6 +344,16 @@ struct acpi_handle_node {
* function returns a pointer to its data structure. The caller must
* decrement the reference count by calling pci_dev_put().
* If no device is found, %NULL is returned.
+ *
+ * XXX: You may be surprised at the results if you call this interface
+ * with a handle to a PCI root bridge and expect to get a pci_dev back.
+ * The PCI specification does not require a PCI root bridge to present
+ * configuration space, and thus may not have a valid associated pci_dev.
+ *
+ * [nb, all P2P bridges _are_ required to present configuration space]
+ *
+ * A PCI root bridge that presents config space is referred to as
+ * "materialized"; its converse is "non-materialized".
*/
struct pci_dev *acpi_get_pci_dev(acpi_handle handle)
{
@@ -385,6 +395,11 @@ struct pci_dev *acpi_get_pci_dev(acpi_handle handle)
* Now, walk back down the PCI device tree until we return to our
* original handle. Assumes that everything between the PCI root
* bridge and the device we're looking for must be a P2P bridge.
+ *
+ * Note! It's possible for ACPI to describe a non-existent PCI device
+ * due to either hotplug or a namespace shared across different
+ * platforms with just enable or present bits to mask them out from
+ * the initial PCI scan. So take care to check for a NULL pdev.
*/
list_for_each_entry(node, &device_list, node) {
acpi_handle hnd = node->handle;
Recent commit 412af978 (ACPI: video: prevent NULL deref in acpi_get_pci_dev()) was added to prevent a boot oops. Update the implementation with some notes and analysis as to why the fix is correct. Cc: Jesse Barnes <jbarnes@virtuousgeek.org> Cc: Troy Moure <twmoure@szypr.net> Signed-off-by: Alex Chiang <achiang@hp.com> --- -- To unsubscribe from this list: send the line "unsubscribe linux-acpi" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html