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

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Message-ID: <2025030905-claim-hardiness-4e7b@gregkh>
Date: Sun, 9 Mar 2025 09:54:16 +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 09:52:38AM +0100, 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?
> 
> > 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?
> 
> And what other drivers use this controller, just normal Linux drivers,
> or vendor-specific ones?
> 
> > Audio - a driver for the T2 audio interface, currently only audio
> > output is supported.
> 
> Again, is this a platform device or does it sit on the BCE "bus" you
> will create here?

Also, it looks like you are creating some new user/kernel apis here
(i.e. a char device for a USB host controller?)  So those need to be
explained a lot as to what they are for and who is using them as I
really don't understand their need, nor know what userspace code
controls them.

thanks,

greg k-h