linux-kernel - Re: [PATCH v2] usb: typec: ucsi: Mark dGPUs as DEVICE scope

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Message-ID: <85845b5e-4c9d-4a2d-9d81-c49c82380177@amd.com>
Date:   Sun, 21 May 2023 07:59:45 -0500
From:   Mario Limonciello <mario.limonciello@....com>
To:     Gregor Riepl <onitake@...il.com>
Cc:     linux-i2c@...r.kernel.org, linux-pm@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-usb@...r.kernel.org,
        Evan.Quan@....com, Lijo.Lazar@....com, Sanket.Goswami@....com,
        heikki.krogerus@...ux.intel.com, ajayg@...dia.com,
        andriy.shevchenko@...ux.intel.com
Subject: Re: [PATCH v2] usb: typec: ucsi: Mark dGPUs as DEVICE scope

On 5/21/23 04:23, Gregor Riepl wrote:
>> As the power supply for a dGPU is only for powering devices connected
>> to dGPU, create a device property to indicate that the UCSI endpoint
>> is only for the scope of `POWER_SUPPLY_SCOPE_DEVICE`.
> 
> Is this a given fact?

At least for today's eGPU enclosures; yes.

> 
> I could imagine that a dGPU device would be capable of feeding power 
> back into the system, for example when an external docking station or 
> display device has a power supply connected to it.
> 
> Although I don't think it's possible (or safe) with a desktop system, 
> maybe a portable computer with a discrete GPU would be able to do this?

If such a hardware design was created you should actually have two USCI 
power supplies.

The PD controller or TCPC for the portable computer should provide one 
to represent the connection to the eGPU and the dGPU should provide one
to represent the connection to the dGPU.

The one from the portable computer will be marked 'system' and the dGPU 
would be 'device.'