linux-kernel - [PATCH] usb: xhci: fixes lost of data for xHCI Cadence Controllers

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Message-ID:
 <PH7PR07MB9538B91A187B4EB8654BB2EBDD8C2@PH7PR07MB9538.namprd07.prod.outlook.com>
Date: Mon, 19 Aug 2024 04:58:44 +0000
From: Pawel Laszczak <pawell@...ence.com>
To: "mathias.nyman@...el.com" <mathias.nyman@...el.com>
CC: "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "peter.chen@...nel.org" <peter.chen@...nel.org>,
        "linux-usb@...r.kernel.org"
	<linux-usb@...r.kernel.org>,
        "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>,
        "stable@...r.kernel.org"
	<stable@...r.kernel.org>
Subject: [PATCH] usb: xhci: fixes lost of data for xHCI Cadence Controllers

Stream endpoint can skip part of TD during next transfer initialization
after beginning stopped during active stream data transfer.
The Set TR Dequeue Pointer command does not clear all internal
transfer-related variables that position stream endpoint on transfer ring.

USB Controller stores all endpoint state information within RsvdO fields
inside endpoint context structure. For stream endpoints, all relevant
information regarding particular StreamID is stored within corresponding
Stream Endpoint context.
Whenever driver wants to stop stream endpoint traffic, it invokes
Stop Endpoint command which forces the controller to dump all endpoint
state-related variables into RsvdO spaces into endpoint context and stream
endpoint context. Whenever driver wants to reinitialize endpoint starting
point on Transfer Ring, it uses the Set TR Dequeue Pointer command
to update dequeue pointer for particular stream in Stream Endpoint
Context. When stream endpoint is forced to stop active transfer in the
middle of TD, it dumps an information about TRB bytes left in RsvdO fields
in Stream Endpoint Context which will be used in next transfer
initialization to designate starting point for XDMA. This field is not
cleared during Set TR Dequeue Pointer command which causes XDMA to skip
over transfer ring and leads to data loss on stream pipe.

Patch fixes this by clearing out all RsvdO fields before initializing new
transfer via that StreamID.

Field Rsvd0 is reserved field, so patch should not have impact for other
xHCI controllers.

Fixes: 3d82904559f4 ("usb: cdnsp: cdns3 Add main part of Cadence USBSSP DRD Driver")
cc: <stable@...r.kernel.org>
Signed-off-by: Pawel Laszczak <pawell@...ence.com>
---
 drivers/usb/host/xhci-ring.c | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/drivers/usb/host/xhci-ring.c b/drivers/usb/host/xhci-ring.c
index 1dde53f6eb31..7fc1c4efcae2 100644
--- a/drivers/usb/host/xhci-ring.c
+++ b/drivers/usb/host/xhci-ring.c
@@ -1385,7 +1385,20 @@ static void xhci_handle_cmd_set_deq(struct xhci_hcd *xhci, int slot_id,
 		if (ep->ep_state & EP_HAS_STREAMS) {
 			struct xhci_stream_ctx *ctx =
 				&ep->stream_info->stream_ctx_array[stream_id];
+			u32 edtl;
+
 			deq = le64_to_cpu(ctx->stream_ring) & SCTX_DEQ_MASK;
+			edtl = EVENT_TRB_LEN(le32_to_cpu(ctx->reserved[1]));
+
+			/*
+			 * Existing Cadence xHCI controllers store some endpoint state information
+			 * within Rsvd0 fields of Stream Endpoint context. This field is not
+			 * cleared during Set TR Dequeue Pointer command which causes XDMA to skip
+			 * over transfer ring and leads to data loss on stream pipe.
+			 * To fix this issue driver must clear Rsvd0 field.
+			 */
+			ctx->reserved[1] = 0;
+			ctx->reserved[0] = cpu_to_le32(edtl);
 		} else {
 			deq = le64_to_cpu(ep_ctx->deq) & ~EP_CTX_CYCLE_MASK;
 		}
-- 
2.43.0