From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from casper.infradead.org (casper.infradead.org [90.155.50.34]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 34C661EB9F2 for ; Mon, 21 Apr 2025 16:35:52 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=90.155.50.34 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1745253355; cv=none; b=FrbVFf16GxzZyPdAKG5PyfhqSFJEkVWR52XUSD7egOVH+qYj65nRxh3wavGGwM+qejtbR13WtiWBa7IznQcdqhrs3T9MPCnR1YFIRiooU+y1yz9BhD6l8YcuNkCBtCnlqVn1RUNzJIYfwcFJS9lQxM9EyN3o6IGWk9MnvYITWiE= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1745253355; c=relaxed/simple; bh=5SUzXHMnJ8ZA8NFrXvxDJyChyzOu2g6SoeD0bI97gJc=; h=Date:From:To:Cc:Subject:Message-ID:MIME-Version:Content-Type: Content-Disposition; b=GNou9Le4bWMvxz+3jAkKubQePyXiU3ukwYjBM7K8aiq0udQMEw3UW2Cn/4Q/2VS5hYOCCxvtQNL7KBg1VQHYRSttBbBv4UbjnToydTFlID49uvOiGd0qGntebRIKWHpQs79xjC9K/Cd+Hdsc0qpqw1CvGwrFTOeALYs7uIVJbko= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org; spf=none smtp.mailfrom=infradead.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b=jFRxqYUJ; arc=none smtp.client-ip=90.155.50.34 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=infradead.org Authentication-Results: smtp.subspace.kernel.org; spf=none smtp.mailfrom=infradead.org Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="jFRxqYUJ" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=Content-Type:MIME-Version:Message-ID: Subject:Cc:To:From:Date:Sender:Reply-To:Content-Transfer-Encoding:Content-ID: Content-Description:In-Reply-To:References; bh=5SUzXHMnJ8ZA8NFrXvxDJyChyzOu2g6SoeD0bI97gJc=; b=jFRxqYUJLEl99kv9YdDuTS/oiD svrKKJ+ZVkvNWOOBMyXrBFowAgjTnQUhDFOh4H/HDsSoeC3vDYYGCTm/DmNGrMvZxLoAquLDGmB2d moc9aHANao411kH/veYBZ4dpMb+fSUSkFrBIxdyZrAwi/2MAwFTBsfNLyDPnxgGuyDUYr6K9kNepZ qSINWvqedavKkW1mlE+nwDmP0q4fY5gj0YcuMrWrKEPfLVmHyi4QFxrrdfUf375mWCPqzcWC4H8cf Kjz1kOQMr99yw61d0q08A40J0e9B221wL1S3RvEkolV/BpfK7+jAzHafLzeY6HB2AwqNW+dnrkKtl HgbxhcQw==; Received: from 77-249-17-252.cable.dynamic.v4.ziggo.nl ([77.249.17.252] helo=noisy.programming.kicks-ass.net) by casper.infradead.org with esmtpsa (Exim 4.98.2 #2 (Red Hat Linux)) id 1u6u7a-00000002utC-1wp3; Mon, 21 Apr 2025 16:35:50 +0000 Received: by noisy.programming.kicks-ass.net (Postfix, from userid 1000) id 4DD8630057E; Mon, 21 Apr 2025 18:35:49 +0200 (CEST) Date: Mon, 21 Apr 2025 18:35:49 +0200 From: Peter Zijlstra To: andreas.noever@gmail.com, michael.jamet@intel.com, westeri@kernel.org, YehezkelShB@gmail.com Cc: linux-usb@vger.kernel.org Subject: Thunderbolt display chaining Message-ID: <20250421163549.GA40412@noisy.programming.kicks-ass.net> 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=us-ascii Content-Disposition: inline Hi guys, I got two Dell U2725QE screens, that can do 4k@120Hz. I'm trying to daisy chain them on thunderbolt 4. Using a windows laptop (Thinkpad X1) it all 'just' works, and both screens are running 4k@60Hz, all good. Using a Linux laptop (Thinkpad X13 Gen2i -- tigerlake) it sorta works. It drives the first at 4k@120Hz and the second at 4k@30Hz, which is kinda terrible. Trying to manually set the first screen to 60Hz works, but doesn't appear to enable me to then manually set the second screen to 60, it's stuck at 30 :-( Using some Tigerlake NUC, I only get a single screen at 4k120Hz and nothing at all on the second screen. I tried having a quick look at tb.c, and it has this bandwidth calculation in tb_available_bandwidth(), but I'm not quite sure where to start poking. Help?