From: Mika Westerberg <mika.westerberg@linux.intel.com>
To: diego.sure@gmail.com
Cc: "Imre Deak" <imre.deak@intel.com>,
dri-devel@lists.freedesktop.org,
"Uma Shankar" <uma.shankar@intel.com>,
"Ville Syrjälä" <ville.syrjala@linux.intel.com>,
"Maarten Lankhorst" <maarten.lankhorst@linux.intel.com>,
"Maxime Ripard" <mripard@kernel.org>,
"Thomas Zimmermann" <tzimmermann@suse.de>,
"David Airlie" <airlied@gmail.com>,
"Simona Vetter" <simona@ffwll.ch>,
"Mika Westerberg" <westeri@kernel.org>,
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
Date: Mon, 2 Nov 2026 14:01:45 +0100 [thread overview]
Message-ID: <20261102130145.GU158991@black.igk.intel.com> (raw)
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 <diego.sure@gmail.com>
>
> 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.
prev parent reply other threads:[~2026-11-02 13:02 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-10-31 0:18 Diego Noguês via B4 Relay
2026-11-02 13:01 ` Mika Westerberg [this message]
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