PCI: Document hybrid devres hazards

These functions:

  pci_request_region()
  pci_request_regions()
  pci_request_regions_exclusive()
  pci_request_selected_regions()
  pci_request_selected_regions_exclusive()
  pci_intx()

are "hybrid" functions that are managed if pcim_enable_device() has been
called, but unmanaged otherwise.

This is confusing and has already caused a bug (in 8558de401b5f
("drm/vboxvideo: use managed pci functions")) because users believe all PCI
functions, such as pci_iomap_range(), can become managed that way, which is
not the case.

Add comments to the relevant functions' docstrings that warn users about
this behavior.

Link: https://lore.kernel.org/r/20240613115032.29098-7-pstanner@redhat.com
Signed-off-by: Philipp Stanner <pstanner@redhat.com>
Signed-off-by: Krzysztof Wilczyński <kwilczynski@kernel.org>
[bhelgaas: commit log]
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>

1 files changed, 16 insertions, 0 deletions

diff --git a/drivers/pci/iomap.c b/drivers/pci/iomap.c
index c9725428e387..a715a4803c95 100644
--- a/drivers/pci/iomap.c
+++ b/drivers/pci/iomap.c
@@ -23,6 +23,10 @@
  *
  * @maxlen specifies the maximum length to map. If you want to get access to
  * the complete BAR from offset to the end, pass %0 here.
+ *
+ * NOTE:
+ * This function is never managed, even if you initialized with
+ * pcim_enable_device().
  * */
 void __iomem *pci_iomap_range(struct pci_dev *dev,
 			      int bar,
@@ -63,6 +67,10 @@ EXPORT_SYMBOL(pci_iomap_range);
  *
  * @maxlen specifies the maximum length to map. If you want to get access to
  * the complete BAR from offset to the end, pass %0 here.
+ *
+ * NOTE:
+ * This function is never managed, even if you initialized with
+ * pcim_enable_device().
  * */
 void __iomem *pci_iomap_wc_range(struct pci_dev *dev,
 				 int bar,
@@ -106,6 +114,10 @@ EXPORT_SYMBOL_GPL(pci_iomap_wc_range);
  *
  * @maxlen specifies the maximum length to map. If you want to get access to
  * the complete BAR without checking for its length first, pass %0 here.
+ *
+ * NOTE:
+ * This function is never managed, even if you initialized with
+ * pcim_enable_device(). If you need automatic cleanup, use pcim_iomap().
  * */
 void __iomem *pci_iomap(struct pci_dev *dev, int bar, unsigned long maxlen)
 {
@@ -127,6 +139,10 @@ EXPORT_SYMBOL(pci_iomap);
  *
  * @maxlen specifies the maximum length to map. If you want to get access to
  * the complete BAR without checking for its length first, pass %0 here.
+ *
+ * NOTE:
+ * This function is never managed, even if you initialized with
+ * pcim_enable_device().
  * */
 void __iomem *pci_iomap_wc(struct pci_dev *dev, int bar, unsigned long maxlen)
 {