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Sat, 03 Oct 2026 20:14:50 -0700 (PDT) Received: from hu-faisalh-hyd.qualcomm.com ([202.46.23.25]) by smtp.gmail.com with ESMTPSA id 5a478bee46e88-35127136c44sm1049634eec.9.2026.10.03.20.14.47 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sat, 03 Oct 2026 20:14:49 -0700 (PDT) From: Faisal Hassan To: Thinh Nguyen , Greg Kroah-Hartman Cc: Felipe Balbi , linux-usb@vger.kernel.org, linux-kernel@vger.kernel.org, faisal.hassan@oss.qualcomm.com Subject: [PATCH] usb: dwc3: gadget: linearize SG requests that exceed the TRB cache Date: Sun, 4 Oct 2026 08:44:45 +0530 Message-Id: <20261004031445.1450196-1-faisal.hassan@oss.qualcomm.com> X-Mailer: git-send-email 2.34.1 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Authority-Analysis: v=2.4 cv=cf5HPXDM c=1 sm=1 tr=0 ts=6ac1c4ac cx=c_pps a=cFYjgdjTJScbgFmBucgdfQ==:117 a=ZePRamnt/+rB5gQjfz0u9A==:17 a=660iZSQnnn4A:10 a=s4-Qcg_JpJYA:10 a=VkNPw1HP01LnGYTKEx00:22 a=u7WPNUs3qKkmUXheDGA7:22 a=rJkE3RaqiGZ5pbrm-msn:22 a=VwQbUJbxAAAA:8 a=EUspDBNiAAAA:8 a=5kJKJXIRvc014F3nmKsA:9 a=scEy_gLbYbu1JhEsrz4S:22 X-Proofpoint-ORIG-GUID: aN3zdPjyvdYT_JbBrQ86enQiMAFm1km9 X-Proofpoint-GUID: aN3zdPjyvdYT_JbBrQ86enQiMAFm1km9 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYxMDA0MDAxMiBTYWx0ZWRfX/dwES+OsSILl hpaNFB9PWORTTeL7tlF7OkrnhQ7vty129fa7NZ7/UQ23vMnfhAiQ9ymuGrdau8zmhJQpT/JqEpg u3Qea0pdq7ITkSPIRaq7Aj9NbIRokTjpCc8YGQngPHOtODKnM4u27Pkc/hQppjuHCuE5IlXQuJr l6WmY3hMC4FvMf5jkYzlmKUfEdAhZN2t27qlO8nq9HYHEe9+oNeLF58tAla3fq2AFaWCdeP5RCL HhIPTlMkq8MRp0UJzdI4pwOubaZ02+RWyEVghtV30FEerkpcndIpvBk1uQw21GdvtScw9eWB95/ WZ5Sw3pvWnuLT/8BrDI1E5ZqZjpGwuf2jqgCF/LZnWPSX2w+R1EcixhWJZSyXkIPC2UwCW/TJ4x +wR6/8PeiiFsIAd4a34XMVzuZEGhSTy14Fv7UTbwEE8txUDKyiMpbfs5Dat7OQaVx3/E/kykJsm +ERs8TFjq+h5lHgPW8g== X-Proofpoint-Spam-Info: AW1haW4tMjYxMDA0MDAxMiBTYWx0ZWRfX2Ofv6n11yZ6s x93Nbxu/DWaqRH6grFsUeBRKaiqAiMgiRwsU+vFPzF2hQ9ElDxGkYLXBpMX00n7qREhCoRnkZEB ltWNLW2bwhI+JL3LsvervRALwGNPLio= X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1176,Hydra:6.1.134,FMLib:17.12.100.49 definitions=2026-10-03_04,2026-10-02_02,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 lowpriorityscore=0 malwarescore=0 spamscore=0 suspectscore=0 bulkscore=0 priorityscore=1501 clxscore=1015 adultscore=0 impostorscore=0 phishscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2609040000 definitions=main-2610040012 The controller prefetches the TRBs of a transfer into an internal cache that holds DWC_USB3_CACHE_TRBS_PER_TRANSFER entries. Databook 4.2.3.3 requires that the number of chained TRBs needed to construct a single packet never exceeds (DWC_USB3_CACHE_TRBS_PER_TRANSFER - 1), where the -1 accounts for the one Link TRB that may be part of the chain when a transfer wraps the TRB ring. The cache never holds more than 15 TRBs however the core was configured, so the usable budget is min(GHWPARAMS4[5:0] - 1, 15) data TRBs per packet. Each scatter-gather entry of a request is queued as one TRB, so a gadget function driver that hands down an IN request whose entries are smaller than MaxPacketSize can exceed that budget with no way of knowing it. On a SuperSpeed bulk IN endpoint, a 1024-byte request scattered across 16 pages of 64 bytes needs 16 chained TRBs for its single packet, one more than the controller can cache: the controller never assembles the packet, the endpoint keeps responding NRDY and the request never completes. The same request runs fine at High-Speed, where the 512-byte MaxPacketSize splits it into two packets of 8 TRBs each. Walk the scatter-gather list of IN requests before mapping them, counting the TRBs each packet would be built from, and copy the request into a single contiguous buffer when a packet would exceed the budget. The original usb_request fields are restored on completion, so function drivers stay independent of the controller limitation. The host side already applies the equivalent workaround unconditionally for every dwc3 instance through XHCI_SG_TRB_CACHE_SIZE_QUIRK. A request that trips this check cannot be transferred at all, so applying the workaround unconditionally can only turn a stalled endpoint into one extra copy. That copy is a GFP_ATOMIC allocation of the request length, which reaches order-4 for a 64 KiB request, but it is only reached by requests that would otherwise never complete. Fixes: eeb720fb21d6 ("usb: dwc3: gadget: add support for SG lists") Cc: stable@vger.kernel.org Signed-off-by: Faisal Hassan --- drivers/usb/dwc3/core.h | 15 +++++ drivers/usb/dwc3/gadget.c | 130 +++++++++++++++++++++++++++++++++++++- 2 files changed, 144 insertions(+), 1 deletion(-) diff --git a/drivers/usb/dwc3/core.h b/drivers/usb/dwc3/core.h index 608daeb7ef10..af71abaac8ed 100644 --- a/drivers/usb/dwc3/core.h +++ b/drivers/usb/dwc3/core.h @@ -386,6 +386,7 @@ #define DWC3_GHWPARAMS3_FSPHY_IFC_ENA 1 /* Global HWPARAMS4 Register */ +#define DWC3_GHWPARAMS4_CACHE_TRBS_PER_TRANSFER(n) ((n) & GENMASK(5, 0)) #define DWC3_GHWPARAMS4_HIBER_SCRATCHBUFS(n) (((n) & (0x0f << 13)) >> 13) #define DWC3_MAX_HIBER_SCRATCHBUFS 15 @@ -714,6 +715,7 @@ struct dwc3_event_buffer { #define DWC3_EP_DIRECTION_RX false #define DWC3_TRB_NUM 256 +#define DWC3_TRB_CACHE_MAX 15 /** * struct dwc3_ep - device side endpoint representation @@ -951,8 +953,15 @@ struct dwc3_hwparams { * @trb: pointer to struct dwc3_trb * @trb_dma: DMA address of @trb * @num_trbs: number of TRBs used by this request + * @sg_trb_cache_buf: temporary linear buffer the scatter-gather list is + * copied into when it exceeds the TRB cache budget + * @sg_trb_cache_sg: scatter-gather list replaced by @sg_trb_cache_buf + * @sg_trb_cache_num_sgs: number of entries in @sg_trb_cache_sg + * @sg_trb_cache_orig_buf: request buffer replaced by @sg_trb_cache_buf * @direction: IN or OUT direction flag * @mapped: true when request has been dma-mapped + * @sg_trb_cache_bounced: true while this request is queued through + * @sg_trb_cache_buf instead of its scatter-gather list */ struct dwc3_request { struct usb_request request; @@ -978,8 +987,14 @@ struct dwc3_request { unsigned int num_trbs; + void *sg_trb_cache_buf; + struct scatterlist *sg_trb_cache_sg; + unsigned int sg_trb_cache_num_sgs; + void *sg_trb_cache_orig_buf; + unsigned int direction:1; unsigned int mapped:1; + unsigned int sg_trb_cache_bounced:1; }; /* diff --git a/drivers/usb/dwc3/gadget.c b/drivers/usb/dwc3/gadget.c index f245e66cd13d..2165c80c7b00 100644 --- a/drivers/usb/dwc3/gadget.c +++ b/drivers/usb/dwc3/gadget.c @@ -190,6 +190,22 @@ static void dwc3_ep_inc_deq(struct dwc3_ep *dep) dwc3_ep_inc_trb(&dep->trb_dequeue); } +static void dwc3_gadget_restore_sg_trb_cache_buf(struct dwc3_request *req) +{ + if (!req->sg_trb_cache_bounced) + return; + + req->request.buf = req->sg_trb_cache_orig_buf; + req->request.sg = req->sg_trb_cache_sg; + req->request.num_sgs = req->sg_trb_cache_num_sgs; + kfree(req->sg_trb_cache_buf); + req->sg_trb_cache_buf = NULL; + req->sg_trb_cache_sg = NULL; + req->sg_trb_cache_num_sgs = 0; + req->sg_trb_cache_orig_buf = NULL; + req->sg_trb_cache_bounced = false; +} + static void dwc3_gadget_del_and_unmap_request(struct dwc3_ep *dep, struct dwc3_request *req, int status) { @@ -206,6 +222,8 @@ static void dwc3_gadget_del_and_unmap_request(struct dwc3_ep *dep, usb_gadget_unmap_request_by_dev(dwc->sysdev, &req->request, req->direction); + dwc3_gadget_restore_sg_trb_cache_buf(req); + req->trb = NULL; trace_dwc3_gadget_giveback(req); @@ -1474,6 +1492,110 @@ static int dwc3_prepare_last_sg(struct dwc3_ep *dep, return num_trbs; } +/* + * Each scatter-gather entry is queued as one TRB, so an IN request backed by + * entries smaller than MaxPacketSize can need more chained TRBs to construct a + * single packet than the controller is able to cache. Databook 4.2.3.3 limits + * the chained TRBs a single packet may be built from to + * (DWC_USB3_CACHE_TRBS_PER_TRANSFER - 1), where the -1 accounts for the single + * Link TRB the controller walks as part of the chain when a transfer wraps the + * TRB ring. The cache itself never holds more than DWC3_TRB_CACHE_MAX TRBs, so + * clamp the limit for cores built with a larger parameter. + * + * Walk the scatter-gather list counting the TRBs each packet would be built + * from, and report the requests that exceed that budget. + */ +static bool dwc3_gadget_sg_trb_cache_limit(struct dwc3_ep *dep, + struct dwc3_request *req) +{ + struct dwc3 *dwc = dep->dwc; + struct scatterlist *sg; + unsigned int cache_depth; + unsigned int max_trbs; + unsigned int maxp; + unsigned int fill = 0; + unsigned int trbs = 0; + int i; + + if (!req->direction || !req->request.num_sgs) + return false; + + if (req->request.sg_was_mapped || req->request.length == 0) + return false; + + cache_depth = DWC3_GHWPARAMS4_CACHE_TRBS_PER_TRANSFER(dwc->hwparams.hwparams4); + if (cache_depth < 2) + return false; + + max_trbs = min_t(unsigned int, cache_depth - 1, DWC3_TRB_CACHE_MAX); + + /* + * A list no longer than the budget cannot exceed it, whatever the + * individual entry sizes are. + */ + if (req->request.num_sgs <= max_trbs) + return false; + + maxp = usb_endpoint_maxp(dep->endpoint.desc); + + for_each_sg(req->request.sg, sg, req->request.num_sgs, i) { + unsigned int len = sg->length; + + trbs++; + + while (fill + len >= maxp) { + len -= maxp - fill; + if (trbs > max_trbs) + return true; + + fill = 0; + trbs = len ? 1 : 0; + } + + fill += len; + } + + /* The transfer may end with a short packet. */ + return fill && trbs > max_trbs; +} + +static int dwc3_gadget_linearize_sg_request(struct dwc3_ep *dep, + struct dwc3_request *req) +{ + void *buf; + size_t copied; + + if (!dwc3_gadget_sg_trb_cache_limit(dep, req)) + return 0; + + buf = kmalloc(req->request.length, GFP_ATOMIC); + if (!buf) + return -ENOMEM; + + copied = sg_pcopy_to_buffer(req->request.sg, req->request.num_sgs, + buf, req->request.length, 0); + if (copied != req->request.length) { + kfree(buf); + return -EINVAL; + } + + dev_dbg(dep->dwc->dev, + "%s: linearize SG request len=%u num_sgs=%u exceeding TRB cache\n", + dep->name, req->request.length, req->request.num_sgs); + + req->sg_trb_cache_buf = buf; + req->sg_trb_cache_sg = req->request.sg; + req->sg_trb_cache_num_sgs = req->request.num_sgs; + req->sg_trb_cache_orig_buf = req->request.buf; + req->sg_trb_cache_bounced = true; + + req->request.buf = buf; + req->request.sg = NULL; + req->request.num_sgs = 0; + + return 0; +} + static int dwc3_prepare_trbs_sg(struct dwc3_ep *dep, struct dwc3_request *req) { @@ -1630,10 +1752,16 @@ static int dwc3_prepare_trbs(struct dwc3_ep *dep) list_for_each_entry_safe(req, n, &dep->pending_list, list) { struct dwc3 *dwc = dep->dwc; + ret = dwc3_gadget_linearize_sg_request(dep, req); + if (ret) + return ret; + ret = usb_gadget_map_request_by_dev(dwc->sysdev, &req->request, dep->direction); - if (ret) + if (ret) { + dwc3_gadget_restore_sg_trb_cache_buf(req); return ret; + } req->start_sg = req->request.sg; req->num_pending_sgs = req->request.num_mapped_sgs; base-commit: 639df5d23876a548b86fe6526bed8b97edf64d96 -- 2.34.1