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Fri, 04 Sep 2026 11:20:28 -0700 (PDT) From: Hanh Kieu To: geraldogabriel@gmail.com, perex@perex.cz, tiwai@suse.com Cc: linux-sound@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] ALSA: usb-audio: add Pioneer DJ DDJ-SZ support Date: Fri, 4 Sep 2026 11:20:23 -0700 Message-ID: <20260904182023.4486-1-hhkieu@gmail.com> X-Mailer: git-send-email 2.47.3 In-Reply-To: References: Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Geraldo Nascimento wrote: > Are you sure is_pioneer_implicit_fb() isn't returning false and you're > picking up on a generic sync ep instead? > > You should double-check that function is returning true or false because > it will return false when USB_ENDPOINT_USAGE_IMPLICIT_FB isn't > set on bmAttributes of a Isochronous IN EP. Good catch, thanks -- I checked against the real device rather than assuming. lsusb -v on the DDJ-SZ shows both endpoints (0x01 OUT, 0x82 IN) as Isochronous / Asynchronous with Usage Type = Data (bmAttributes = 0x05). is_pioneer_implicit_fb() accepts the capture endpoint's usage being either USB_ENDPOINT_USAGE_DATA or USB_ENDPOINT_USAGE_IMPLICIT_FB, not IMPLICIT_FB exclusively, so Data usage does pass that check. I also traced snd_usb_parse_implicit_fb_quirk()'s dispatch order for this device to make sure nothing generic intercepts first: no fixed or capture quirk-table entry matches 08e4:0191, it isn't UAC2 (bInterfaceClass is vendor-spec, not USB_CLASS_AUDIO), and it isn't the Roland vendor ID. So is_pioneer_implicit_fb() is the function actually being reached and returning true for this device, not a coincidental generic fallback. Happy to add a comment near the quirk-table entry noting the real bmAttributes value if that would help future readers. Thanks, Hanh Kieu