[PATCH v1] PCI/TPH: fold reserved completer encoding in get_rp_completer_type()

[PATCH v1] PCI/TPH: fold reserved completer encoding in get_rp_completer_type()

[Zhiping Zhang]

get_rp_completer_type() returns the Root Port's "TPH Completer
Supported" field (bits 13:12 of Device Capabilities 2) verbatim. The
0b10 encoding is reserved, but pcie_enable_tph() feeds the raw value
into the requester type:

	pdev->tph_req_type = min(pdev->tph_req_type, rp_req_type);

and later writes tph_req_type to the TPH Requester Enable field, which
only defines 0b00 (disable), 0b01 (TPH only) and 0b11 (extended TPH).
If a Root Port ever presents the reserved 0b10, that value could be
written back to hardware, risking undefined behavior.

Fold the reserved encoding into "not supported" so only the three
defined values can propagate.

Fixes: f69767a1ada3 ("PCI: Add TLP Processing Hints (TPH) support")
Signed-off-by: Zhiping Zhang <zhipingz@meta.com>
---
 drivers/pci/tph.c | 18 ++++++++++++++++--
 1 file changed, 16 insertions(+), 2 deletions(-)

diff --git a/drivers/pci/tph.c b/drivers/pci/tph.c
index 655ffd60e62f..28c8d6676fc2 100644
--- a/drivers/pci/tph.c
+++ b/drivers/pci/tph.c
@@ -196,7 +196,14 @@ u16 pcie_tph_get_st_table_size(struct pci_dev *pdev)
 }
 EXPORT_SYMBOL(pcie_tph_get_st_table_size);
 
-/* Return device's Root Port completer capability */
+/*
+ * Return device's Root Port completer capability.
+ *
+ * The "TPH Completer Supported" field (bits 13:12 of Device Capabilities 2)
+ * has a reserved 0b10 encoding. Fold it into "not supported" so only the
+ * three defined values can propagate into pdev->tph_req_type via the min()
+ * in pcie_enable_tph().
+ */
 static u8 get_rp_completer_type(struct pci_dev *pdev)
 {
 	struct pci_dev *rp;
@@ -211,7 +218,14 @@ static u8 get_rp_completer_type(struct pci_dev *pdev)
 	if (ret)
 		return 0;
 
-	return FIELD_GET(PCI_EXP_DEVCAP2_TPH_COMP_MASK, reg);
+	switch (FIELD_GET(PCI_EXP_DEVCAP2_TPH_COMP_MASK, reg)) {
+	case PCI_EXP_DEVCAP2_TPH_COMP_TPH_ONLY:
+		return PCI_EXP_DEVCAP2_TPH_COMP_TPH_ONLY;
+	case PCI_EXP_DEVCAP2_TPH_COMP_EXT_TPH:
+		return PCI_EXP_DEVCAP2_TPH_COMP_EXT_TPH;
+	default:
+		return PCI_EXP_DEVCAP2_TPH_COMP_NONE;
+	}
 }
 
 /* Write tag to ST table - Return 0 if OK, otherwise -errno */
-- 
2.53.0-Meta

Re: [PATCH v1] PCI/TPH: fold reserved completer encoding in get_rp_completer_type()

[sashiko-bot]

> get_rp_completer_type() returns the Root Port's "TPH Completer
> Supported" field (bits 13:12 of Device Capabilities 2) verbatim. The
> 0b10 encoding is reserved, but pcie_enable_tph() feeds the raw value
> into the requester type:
> 
> 	pdev->tph_req_type = min(pdev->tph_req_type, rp_req_type);
> 
> and later writes tph_req_type to the TPH Requester Enable field, which
> only defines 0b00 (disable), 0b01 (TPH only) and 0b11 (extended TPH).
> If a Root Port ever presents the reserved 0b10, that value could be
> written back to hardware, risking undefined behavior.
> 
> Fold the reserved encoding into "not supported" so only the three
> defined values can propagate.
> 
> Fixes: f69767a1ada3 ("PCI: Add TLP Processing Hints (TPH) support")
> Signed-off-by: Zhiping Zhang <zhipingz@meta.com>

Sashiko has reviewed this patch and found no issues. It looks great!

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260713214026.793795-1-zhipingz@meta.com?part=1