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[2001:1c00:3281:1680:7a55:36ff:fe02:cdba]) by smtp.gmail.com with ESMTPSA id a640c23a62f3a-bbe6aa4d524sm445224366b.26.2026.05.04.16.33.15 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 04 May 2026 16:33:16 -0700 (PDT) From: Nicola Lunghi To: mathias.nyman@intel.com, michal.pecio@gmail.com, niklas.neronin@linux.intel.com, gregkh@linuxfoundation.org Cc: linux-usb@vger.kernel.org, linux-kernel@vger.kernel.org, Nicola Lunghi Subject: [PATCH 0/2] xhci: Fix isochronous scheduling gaps on CFC controllers Date: Tue, 5 May 2026 01:31:42 +0200 Message-ID: <20260504233143.10242-2-nick83ola@gmail.com> X-Mailer: git-send-email 2.51.0 Precedence: bulk X-Mailing-List: linux-usb@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit This series addresses a long-standing issue where the xHCI driver introduces frame-aligned gaps in isochronous streams during timing fluctuations. While many USB devices handle these gaps with a minor glitch, professional interfaces like the MOTU 1248 lose internal channel synchronization when these gaps occur. I have identified two specific code paths in xhci-ring.c where these gaps are created: Silent Rescheduling: When a start frame is "late," the driver adds a +1 frame offset, creating an explicit hole in the stream. Ring Drain Race: On CFC-capable controllers, the driver falls back to ASAP scheduling if the ring is momentarily empty, resulting in a jump to a future frame instead of continuing sequentially. Impact on MOTU 1248: The MOTU 1248 is particularly sensitive to stream continuity. The two situations described above cause a shift in the output channels, where audio intended for one set of channels is routed to the wrong physical outputs until the device is reset. Proposed Solution: This series modifies the xHCI driver to prefer sequential scheduling on modern CFC-capable controllers: - Patch 1 removes the silent start_frame_id + 1 reschedule, returning -EINVAL to allow the use of the TRB_SIA (Schedule Immediate After) flag. - Patch 2 expands the CFC sequential condition to check if a periodic completion is in progress, covering the "ring drain" race where a new URB is submitted just as the previous one finishes. These changes build upon recent work by Michał Pecio regarding missed TD handling. Link: https://bugzilla.kernel.org/show_bug.cgi?id=220748 Nicola Lunghi (2): usb: xhci: fix isoc silent reschedule creating stream gap on CFC controllers usb: xhci: fix CFC sequential scheduling lost on ring drain race drivers/usb/host/xhci-ring.c | 42 +++++++++++++++++++++++++----------- 1 file changed, 29 insertions(+), 13 deletions(-) -- 2.51.0