Re: [RFC PATCH] usb: typec: ucsi: acpi: bootstrap PPM on HP systems with empty _DSM func 2

[Heikki Krogerus <heikki.krogerus@linux.intel.com>]

Hi,

On Mon, Apr 20, 2026 at 04:05:47PM +0000, Francesco Orro wrote:
> Hi,
> 
> The attached RFC patch lets ucsi_acpi probe successfully on HP ZBook
> Fury G1i 16 inch (and likely other HP workstations shipping the same
> "UcsiAcpi" SSDT), where _DSM func 2 (READ) is a stub and UCSI_VERSION
> stays 0. Details in the commit message below.

Please report this to HP. We really need to know which version they
support.

> Main open question for the list: is there a known-good pattern for
> ucsi_acpi drivers to avoid disrupting alt-mode state already negotiated
> by BIOS? On cold boot with a Thunderbolt dock attached, the PPM_RESET
> issued by this patch - and later by Linux UCSI core in ucsi_init() -
> tears down the TBT alt-mode the BIOS had set up, and the DP tunnel to
> the dock dies until the user physically replugs. My local workaround
> is to late-load ucsi_acpi via a systemd service after the thunderbolt
> driver has adopted the tunnels, but that feels like papering over a
> design assumption I am missing.

I'm surprised that PPM_RESET has that effect on your system, because
it does not reset the connectors. If you want to reset the connectors
you are expected to explicitly reset each of them before the executing
PPM_RESET. I'm not sure the PPM on this platform is behaving correctly,
so I think you need to contact HP about this too.

> Tested on one machine only. Happy to refine the patch if the direction
> is acceptable.
> 
> Regards,
> Francesco Orro
> 
> ---
> 
> From: Francesco Orro <ncesco@interstellar.eu>
> Date: Mon, 20 Apr 2026 16:40:00 +0200
> Subject: [PATCH v7] usb: typec: ucsi: acpi: bootstrap PPM on systems with empty _DSM func 2

Please avoid attaching the patch to the coverletter like this. It is
a bit confusing. Is this the same patch as the one you've sent
separately in this thread?

thanks,

-- 
heikki