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SubjectRe: Apple Thunderbolt Display chaining
Hi,

On Tue, Aug 09, 2022 at 06:40:54PM +0800, Brad Campbell wrote:
> G'day Mika,
>
>
> On 9/8/22 18:23, Mika Westerberg wrote:
> > Hi,
> >
> > On Mon, Aug 08, 2022 at 09:27:24PM +0800, Brad Campbell wrote:
> >> If I don't authorize the PCIe tunnels and just leave the DP enabled it
> >> works fine also.
> >
> > But you say that it fails on boot when the driver discovers the tunnels,
> > right? So there is really nothing to authorize (they should be already
> > "authorized" by the boot firmware).
> >
> > If I understand correctly this is how it reproduces (the simplest):
> >
> > 1. Connect a single Apple TB1 display to the system
> > 2. Boot it up
> > 3. Wait a while and it hangs
> >
> > If this is the case, then the driver certainly is not creating any
> > PCIe tunnels itself unless there is a bug somewhere.
> >
> > An additional question, does it reproduce with either TB1 display
> > connected or just with specific TB1 display?
> >
>
> No, I've not been clear enough, I'm sorry. I've re-read what I've written below and
> I'm still not sure I'm clear enough.
>
> The firmware never sets anything up.
>
> When I cold boot the machine (from power on), the thunderbolt displays and tunnels
> remain dark until linux initializes the thunderbolt driver the first time.
>
> If I compile the thunderbolt driver into the kernel, or let the initramfs load it
> the displays come up, all PCIe tunnels are established and everything works.
>
> When I reboot the machine (reset button or warm boot), the firmware continues to
> do nothing and all the tunnels remain in place. The machine dies when the thunderbolt
> driver is loaded for a second time.
>
> That might be a reset/warm boot with it compiled in or loaded from iniramfs.
> It may also be me loading it from the command line after booting with it as a
> module and blacklisted.
>
> The problem comes about when the thunderbolt module is loaded while the PCIe tunnels
> are already established.
>
> To reproduce in the easiest manner I compile the thunderbolt driver as a module and
> blacklist it. This prevents it from auto-loading.
>
> I cold boot the machine, let it boot completely then modprobe thunderbolt and authorize
> the tunnels. I then warm boot which lets the kernel detect and init the DP displays
> and detect/configure all the PCIe devices. The thunderbolt driver is not loaded.
>
> The machine comes up, all tunnels are established and all devices work.
>
> If I then modprobe the thunderbolt driver, things break.
>
> This is the hack in my boot script :
>
> # Spark up thunderbolt
> if [ -z "`grep notb /proc/cmdline`" -a -z "`lsusb | grep '05ac:9227'`" ] ; then
> modprobe thunderbolt
> sleep 1
> echo 1 > /sys/bus/thunderbolt/devices/0-3/authorized
> echo 1 > /sys/bus/thunderbolt/devices/0-303/authorized
> reboot
> fi

Thanks for the clarification! How about on macOS side, does it work (I
would expect yes)?

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