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a="2191421" X-IronPort-AV: E=Sophos;i="6.27,191,1787036400"; d="scan'208";a="2191421" Received: from fmviesa001.fm.intel.com ([10.60.135.141]) by orvoesa105.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 02 Nov 2026 05:01:49 -0800 X-CSE-ConnectionGUID: 7v3+O6SmRse+47iagkBWOA== X-CSE-MsgGUID: FVk/xTTMQl2oCXXGju5lfw== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.27,191,1787036400"; d="scan'208";a="6449554" Received: from black.igk.intel.com ([10.91.253.5]) by fmviesa001.fm.intel.com with ESMTP; 02 Nov 2026 05:01:46 -0800 Received: by black.igk.intel.com (Postfix, from userid 1001) id 236A699; Mon, 02 Nov 2026 14:01:45 +0100 (CET) Date: Mon, 2 Nov 2026 14:01:45 +0100 From: Mika Westerberg To: diego.sure@gmail.com Cc: Imre Deak , dri-devel@lists.freedesktop.org, Uma Shankar , Ville =?utf-8?B?U3lyasOkbMOk?= , Maarten Lankhorst , Maxime Ripard , Thomas Zimmermann , David Airlie , Simona Vetter , Mika Westerberg , intel-gfx@lists.freedesktop.org, intel-xe@lists.freedesktop.org, linux-usb@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH RFC] drm/dp_tunnel: Allow BWA when the DP IN adapter does not advertise it Message-ID: <20261102130145.GU158991@black.igk.intel.com> References: <20261031-dp-tunnel-bwa-flag-v1-1-f94ed3179349@gmail.com> X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20261031-dp-tunnel-bwa-flag-v1-1-f94ed3179349@gmail.com> Hi, On Sat, Oct 31, 2026 at 01:18:18AM +0100, Diego Noguês via B4 Relay wrote: > From: Diego Noguês > > On an Alder Lake host (i7-1265U) with a Thunderbolt 4 dock (Dell WD22TB4, > Goshen Ridge) driving two 4K@60 monitors through two DP tunnels, the > monitor whose tunnel is created second is limited to 4K@30. Which monitor > is affected depends only on the order in which they are powered on. > > The thunderbolt driver enables the BW allocation mode (BWA) on both DP IN > adapters: it sets the CM BWA support (DP_USB4_DRIVER_BW_CAPABILITY), a > group ID and the estimated BW. The DP IN adapter, however, never sets > DP_IN_BW_ALLOCATION_MODE_SUPPORT in DP_TUNNELING_CAPABILITIES (0xe000d > reads 0x01), so tunnel_regs_are_valid() rejects the tunnel with: Alder Lake firmware really does not support this and by forcing it to be enabled you may end up in untested code paths and interesting behavior :) BWA was only officially supported starting from Meteor Lake.