Hi, On Sat, Oct 31, 2026 at 01:18:18AM +0100, Diego Noguês via B4 Relay wrote: > From: Diego Noguês <[email protected]> > > 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.
