[PATCH v5 3/7] PCI/ATS: Decouple pci_ats_supported() from pci_prepare_ats()

[Pranjal Shrivastava <praan@google.com>]

Currently, pci_prepare_ats() internally calls pci_ats_supported() and
returns -EINVAL if the device does not support ATS. While this provides
a safety check, it conflates support detection with configuration.

Update pci_prepare_ats() to remove the internal support check. This
decouples support verification from the configuration phase, ensuring
that drivers can distinguish between a device that does not support ATS
and one that has a true configuration error (e.g. STU mismatch).

Update the function documentation to mandate that callers must verify
ATS support (via pci_ats_supported()) before calling pci_prepare_ats().

Signed-off-by: Pranjal Shrivastava <praan@google.com>
---
 drivers/pci/ats.c | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/drivers/pci/ats.c b/drivers/pci/ats.c
index 8057c24b0469..92c2a6bc2dcc 100644
--- a/drivers/pci/ats.c
+++ b/drivers/pci/ats.c
@@ -56,7 +56,9 @@ EXPORT_SYMBOL_GPL(pci_ats_supported);
  * @ps: the IOMMU page shift
  *
  * This must be done by the IOMMU driver on the PF before any VFs are created to
- * ensure that the VF can have ATS enabled.
+ * ensure that the VF can have ATS enabled. Callers must verify that ATS is
+ * supported by the device (e.g. via pci_ats_supported()) before calling this
+ * function.
  *
  * Returns 0 on success, or negative on failure.
  */
@@ -64,9 +66,6 @@ int pci_prepare_ats(struct pci_dev *dev, int ps)
 {
 	u16 ctrl;
 
-	if (!pci_ats_supported(dev))
-		return -EINVAL;
-
 	if (WARN_ON(dev->ats_enabled))
 		return -EBUSY;
 
-- 
2.54.0.823.g6e5bcc1fc9-goog