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From: Peter Zijlstra <peterz@infradead.org>
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
Date: Mon, 21 Apr 2025 18:35:49 +0200	[thread overview]
Message-ID: <20250421163549.GA40412@noisy.programming.kicks-ass.net> (raw)

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?

             reply	other threads:[~2025-04-21 16:35 UTC|newest]

Thread overview: 3+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2025-04-21 16:35 Peter Zijlstra [this message]
2025-04-22  5:05 ` Thunderbolt display chaining Mika Westerberg
2025-04-22  9:12   ` Peter Zijlstra

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