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

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Message-ID: <2025030909-recoup-unafraid-1df0@gregkh>
Date: Sun, 9 Mar 2025 10:48:52 +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 09:41:29AM +0000, Aditya Garg wrote:
> 
> 
> > On 9 Mar 2025, at 3:09 PM, gregkh@...uxfoundation.org wrote:
> > 
> > On Sun, Mar 09, 2025 at 09:28:01AM +0000, Aditya Garg wrote:
> >> 
> >> 
> >>>> On 9 Mar 2025, at 2:46 PM, gregkh@...uxfoundation.org wrote:
> >>> 
> >>> 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?
> >> 
> >> We technically can split up these 3 into separate drivers and put then into their own trees.
> > 
> > That's fine, but you say that the bce code is used by the other drivers,
> > right?  So there is some sort of "tie" between these, and that needs to
> > be properly conveyed in the device tree in sysfs as that will be
> > required for proper resource management.
> 
> Yes there needs to be a tie, basically first establish a communication with the t2 using bce and then the other 2 come into the picture. I did get a basic idea from what the maintainers want, and this will be some work to do. Thanks for your inputs!

If there is "communication" then that's a bus in the driver model
scheme, so just use that, right?

thanks,

greg k-h