usb: xhci: improve TR Dequeue Pointer mask

Address the naming and usage of the TR Dequeue Pointer mask in the xhci driver. The Endpoint Context Field at offset 0x08 is defined as follows:
Bit 0 Dequeue Cycle State (DCS)
Bits 3:1 RsvdZ (Reserved and Zero)
Bits 63:4 TR Dequeue Pointer

When extracting the TR Dequeue Pointer for an Endpoint without Streams, in xhci_handle_cmd_set_deq(), the inverted Dequeue Cycle State mask (~EP_CTX_CYCLE_MASK) is used, inadvertently including the Reserved bits. Although bits 3:1 are typically zero, using the incorrect mask could cause issues.

The existing mask, named "SCTX_DEQ_MASK," is misleading because "SCTX" implies exclusivity to Stream Contexts, whereas the TR Dequeue Pointer is applicable to both Stream and non-Stream Contexts.

Rename the mask to "TR_DEQ_PTR_MASK", utilize GENMASK_ULL() macro and use the mask when handling the TR Dequeue Pointer field.

Function xhci_get_hw_deq() returns the Endpoint Context Field 0x08, either directly from the Endpoint context or a Stream.

Signed-off-by Niklas Neronin <[email protected]>

---
v2:
* Rebased on top of 6.16.
* Combined all 3 patches from v1 into one patch.

 drivers/usb/host/xhci-ring.c | 12 ++++++------
 drivers/usb/host/xhci.h      |  3 ++-
 2 files changed, 8 insertions(+), 7 deletions(-)

drivers/usb/host/xhci-ring.c +5 -5

index ecd757d482c5..d2ccf19292aa 100644
@@ -711,7 +711,7 @@ static int xhci_move_dequeue_past_td(struct xhci_hcd *xhci,
 		return -ENODEV;
 	}
 
-	hw_dequeue = xhci_get_hw_deq(xhci, dev, ep_index, stream_id);
+	hw_dequeue = xhci_get_hw_deq(xhci, dev, ep_index, stream_id) & TR_DEQ_PTR_MASK;
 	new_seg = ep_ring->deq_seg;
 	new_deq = ep_ring->dequeue;
 	new_cycle = le32_to_cpu(td->end_trb->generic.field[3]) & TRB_CYCLE;

@@ -723,7 +723,7 @@ static int xhci_move_dequeue_past_td(struct xhci_hcd *xhci,
 	 */
 	do {
 		if (!hw_dequeue_found && xhci_trb_virt_to_dma(new_seg, new_deq)
-		    == (dma_addr_t)(hw_dequeue & ~0xf)) {
+		    == (dma_addr_t)hw_dequeue) {
 			hw_dequeue_found = true;
 			if (td_last_trb_found)
 				break;

@@ -1066,7 +1066,7 @@ static int xhci_invalidate_cancelled_tds(struct xhci_virt_ep *ep)
 		 */
 		hw_deq = xhci_get_hw_deq(xhci, ep->vdev, ep->ep_index,
 					 td->urb->stream_id);
-		hw_deq &= ~0xf;
+		hw_deq &= TR_DEQ_PTR_MASK;
 
 		if (td->cancel_status == TD_HALTED || trb_in_td(td, hw_deq)) {
 			switch (td->cancel_status) {

@@ -1156,7 +1156,7 @@ static struct xhci_td *find_halted_td(struct xhci_virt_ep *ep)
 
 	if (!list_empty(&ep->ring->td_list)) { /* Not streams compatible */
 		hw_deq = xhci_get_hw_deq(ep->xhci, ep->vdev, ep->ep_index, 0);
-		hw_deq &= ~0xf;
+		hw_deq &= TR_DEQ_PTR_MASK;
 		td = list_first_entry(&ep->ring->td_list, struct xhci_td, td_list);
 		if (trb_in_td(td, hw_deq))
 			return td;

@@ -1481,7 +1481,7 @@ static void xhci_handle_cmd_set_deq(struct xhci_hcd *xhci, int slot_id,
 		u64 deq;
 		/* 4.6.10 deq ptr is written to the stream ctx for streams */
 		if (ep->ep_state & EP_HAS_STREAMS) {
-			deq = le64_to_cpu(stream_ctx->stream_ring) & SCTX_DEQ_MASK;
+			deq = le64_to_cpu(stream_ctx->stream_ring) & TR_DEQ_PTR_MASK;
 
 			/*
 			 * Cadence xHCI controllers store some endpoint state

Quoted 24 lines · Niklas Neronin

Address the naming and usage of the TR Dequeue Pointer mask in the xhci driver. The Endpoint Context Field at offset 0x08 is defined as follows:
Bit 0 Dequeue Cycle State (DCS)
Bits 3:1 RsvdZ (Reserved and Zero)
Bits 63:4 TR Dequeue Pointer

When extracting the TR Dequeue Pointer for an Endpoint without Streams, in xhci_handle_cmd_set_deq(), the inverted Dequeue Cycle State mask (~EP_CTX_CYCLE_MASK) is used, inadvertently including the Reserved bits. Although bits 3:1 are typically zero, using the incorrect mask could cause issues.

The existing mask, named "SCTX_DEQ_MASK," is misleading because "SCTX" implies exclusivity to Stream Contexts, whereas the TR Dequeue Pointer is applicable to both Stream and non-Stream Contexts.

Rename the mask to "TR_DEQ_PTR_MASK", utilize GENMASK_ULL() macro and use the mask when handling the TR Dequeue Pointer field.

Function xhci_get_hw_deq() returns the Endpoint Context Field 0x08, either directly from the Endpoint context or a Stream.

Signed-off-by Niklas Neronin <[email protected]>

---

drivers/usb/host/xhci.h struct xhci_ep_ctx { · line 504

Quoted 12 lines

drivers/usb/host/xhci.h +2 -1

index a20f4e7cd43a..59ff84ba2d4a 100644
@@ -500,7 +500,8 @@ struct xhci_ep_ctx {
 
 /* deq bitmasks */
 #define EP_CTX_CYCLE_MASK		(1 << 0)
-#define SCTX_DEQ_MASK			(~0xfL)
+/* bits 63:4 - TR Dequeue Pointer */
+#define TR_DEQ_PTR_MASK			GENMASK_ULL(63, 4)

I don't care much about this rename, but I can't help but notice that naming is not consistent with the related EP_CTX_CYCLE_MASK above and that it too applies to both types of contexts.

If I wanted to fix this, I would just drop the 'EP_' and 'S' prefixes.