linux-kernel - Re: [PATCH RFC] staging: Add driver to communicate with the T2 Security Chip

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Message-ID: <2025030937-antihero-sandblast-7c87@gregkh>
Date: Sun, 9 Mar 2025 10:14:41 +0100
From: "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>
To: Aditya Garg <gargaditya08@...e.com>
Cc: "bhelgaas@...gle.com" <bhelgaas@...gle.com>,
	"joro@...tes.org" <joro@...tes.org>,
	"will@...nel.org" <will@...nel.org>,
	"robin.murphy@....com" <robin.murphy@....com>,
	"andriy.shevchenko@...ux.intel.com" <andriy.shevchenko@...ux.intel.com>,
	"linux-staging@...ts.linux.dev" <linux-staging@...ts.linux.dev>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
	"iommu@...ts.linux.dev" <iommu@...ts.linux.dev>,
	Aun-Ali Zaidi <admin@...eit.net>, "paul@...rm.io" <paul@...rm.io>,
	Orlando Chamberlain <orlandoch.dev@...il.com>
Subject: Re: [PATCH RFC] staging: Add driver to communicate with the T2
 Security Chip

On Sun, Mar 09, 2025 at 09:03:29AM +0000, Aditya Garg wrote:
> 
> 
> > On 9 Mar 2025, at 2:24 PM, gregkh@...uxfoundation.org wrote:
> > 
> > On Sun, Mar 09, 2025 at 08:40:31AM +0000, Aditya Garg wrote:
> >> From: Paul Pawlowski <paul@...rm.io>
> >> 
> >> This patch adds a driver named apple-bce, to add support for the T2
> >> Security Chip found on certain Macs.
> >> 
> >> The driver has 3 main components:
> >> 
> >> BCE (Buffer Copy Engine) - this is what the files in the root directory
> >> are for. This estabilishes a basic communication channel with the T2.
> >> VHCI and Audio both require this component.
> > 
> > So this is a new "bus" type?  Or a platform resource?  Or something
> > else?
> 
> It's a PCI device

Great, but then is the resources split up into smaller drivers that then
bind to it?  How does the other devices talk to this?

> >> VHCI - this is a virtual USB host controller; keyboard, mouse and
> >> other system components are provided by this component (other
> >> drivers use this host controller to provide more functionality).
> > 
> > I don't understand, why does a security chip have a USB virtual
> > interface in it?  What "devices" hang off of it that are found and
> > enumerated by the host OS?
> 
> The t2 chip not only handles security, but also has a usb hub, which connects the internal keyboard, trackpad, touchbar, webcam, and other internal devices. The external usb ports are separate.

That feels strange, but hey, we've seen worse :)

thanks,

greg k-h