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 8558de401b
("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>

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)
 {

drivers/pci/pci.c

@@ -3900,6 +3900,8 @@ EXPORT_SYMBOL(pci_release_region);
  * @res_name: Name to be associated with resource.
  * @exclusive: whether the region access is exclusive or not
  *
+ * Returns: 0 on success, negative error code on failure.
+ *
  * Mark the PCI region associated with PCI device @pdev BAR @bar as
  * being reserved by owner @res_name.  Do not access any
  * address inside the PCI regions unless this call returns
@@ -3950,6 +3952,8 @@ err_out:
  * @bar: BAR to be reserved
  * @res_name: Name to be associated with resource
  *
+ * Returns: 0 on success, negative error code on failure.
+ *
  * Mark the PCI region associated with PCI device @pdev BAR @bar as
  * being reserved by owner @res_name.  Do not access any
  * address inside the PCI regions unless this call returns
@@ -3957,6 +3961,11 @@ err_out:
  *
  * Returns 0 on success, or %EBUSY on error.  A warning
  * message is also printed on failure.
+ *
+ * NOTE:
+ * This is a "hybrid" function: It's normally unmanaged, but becomes managed
+ * when pcim_enable_device() has been called in advance. This hybrid feature is
+ * DEPRECATED! If you want managed cleanup, use the pcim_* functions instead.
  */
 int pci_request_region(struct pci_dev *pdev, int bar, const char *res_name)
 {
@@ -4007,6 +4016,13 @@ err_out:
  * @pdev: PCI device whose resources are to be reserved
  * @bars: Bitmask of BARs to be requested
  * @res_name: Name to be associated with resource
+ *
+ * Returns: 0 on success, negative error code on failure.
+ *
+ * NOTE:
+ * This is a "hybrid" function: It's normally unmanaged, but becomes managed
+ * when pcim_enable_device() has been called in advance. This hybrid feature is
+ * DEPRECATED! If you want managed cleanup, use the pcim_* functions instead.
  */
 int pci_request_selected_regions(struct pci_dev *pdev, int bars,
 				 const char *res_name)
@@ -4015,6 +4031,19 @@ int pci_request_selected_regions(struct pci_dev *pdev, int bars,
 }
 EXPORT_SYMBOL(pci_request_selected_regions);
 
+/**
+ * pci_request_selected_regions_exclusive - Request regions exclusively
+ * @pdev: PCI device to request regions from
+ * @bars: bit mask of BARs to request
+ * @res_name: name to be associated with the requests
+ *
+ * Returns: 0 on success, negative error code on failure.
+ *
+ * NOTE:
+ * This is a "hybrid" function: It's normally unmanaged, but becomes managed
+ * when pcim_enable_device() has been called in advance. This hybrid feature is
+ * DEPRECATED! If you want managed cleanup, use the pcim_* functions instead.
+ */
 int pci_request_selected_regions_exclusive(struct pci_dev *pdev, int bars,
 					   const char *res_name)
 {
@@ -4032,7 +4061,6 @@ EXPORT_SYMBOL(pci_request_selected_regions_exclusive);
  * successful call to pci_request_regions().  Call this function only
  * after all use of the PCI regions has ceased.
  */
-
 void pci_release_regions(struct pci_dev *pdev)
 {
 	pci_release_selected_regions(pdev, (1 << PCI_STD_NUM_BARS) - 1);
@@ -4051,6 +4079,11 @@ EXPORT_SYMBOL(pci_release_regions);
  *
  * Returns 0 on success, or %EBUSY on error.  A warning
  * message is also printed on failure.
+ *
+ * NOTE:
+ * This is a "hybrid" function: It's normally unmanaged, but becomes managed
+ * when pcim_enable_device() has been called in advance. This hybrid feature is
+ * DEPRECATED! If you want managed cleanup, use the pcim_* functions instead.
  */
 int pci_request_regions(struct pci_dev *pdev, const char *res_name)
 {
@@ -4064,6 +4097,8 @@ EXPORT_SYMBOL(pci_request_regions);
  * @pdev: PCI device whose resources are to be reserved
  * @res_name: Name to be associated with resource.
  *
+ * Returns: 0 on success, negative error code on failure.
+ *
  * Mark all PCI regions associated with PCI device @pdev as being reserved
  * by owner @res_name.  Do not access any address inside the PCI regions
  * unless this call returns successfully.
@@ -4073,6 +4108,11 @@ EXPORT_SYMBOL(pci_request_regions);
  *
  * Returns 0 on success, or %EBUSY on error.  A warning message is also
  * printed on failure.
+ *
+ * NOTE:
+ * This is a "hybrid" function: It's normally unmanaged, but becomes managed
+ * when pcim_enable_device() has been called in advance. This hybrid feature is
+ * DEPRECATED! If you want managed cleanup, use the pcim_* functions instead.
  */
 int pci_request_regions_exclusive(struct pci_dev *pdev, const char *res_name)
 {
@@ -4404,6 +4444,11 @@ void pci_disable_parity(struct pci_dev *dev)
  * @enable: boolean: whether to enable or disable PCI INTx
  *
  * Enables/disables PCI INTx for device @pdev
+ *
+ * NOTE:
+ * This is a "hybrid" function: It's normally unmanaged, but becomes managed
+ * when pcim_enable_device() has been called in advance. This hybrid feature is
+ * DEPRECATED!
  */
 void pci_intx(struct pci_dev *pdev, int enable)
 {