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

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Message-ID: <ef8dcf7a-34ed-4b27-a154-e01bc167d4e6@arm.com>
Date: Mon, 10 Mar 2025 13:49:13 +0000
From: Robin Murphy <robin.murphy@....com>
To: Aditya Garg <gargaditya08@...e.com>,
 "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
 "bhelgaas@...gle.com" <bhelgaas@...gle.com>,
 "joro@...tes.org" <joro@...tes.org>, "will@...nel.org" <will@...nel.org>,
 "andriy.shevchenko@...ux.intel.com" <andriy.shevchenko@...ux.intel.com>
Cc: "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 2025-03-09 8:40 am, 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.
> 
> 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).
> 
> Audio - a driver for the T2 audio interface, currently only audio
> output is supported.
> 
> Currently, suspend and resume for VHCI is broken after a firmware
> update in iBridge since macOS Sonoma.
> 
> Signed-off-by: Paul Pawlowski <paul@...rm.io>
> Signed-off-by: Aditya Garg <gargaditya08@...e.com>
> ---
> drivers/staging/Kconfig                       |   2 +
> drivers/staging/Makefile                      |   1 +
> drivers/staging/apple-bce/Kconfig             |  18 +
> drivers/staging/apple-bce/Makefile            |  28 +
> drivers/staging/apple-bce/apple_bce.c         | 448 ++++++++++
> drivers/staging/apple-bce/apple_bce.h         |  44 +
> drivers/staging/apple-bce/audio/audio.c       | 714 ++++++++++++++++
> drivers/staging/apple-bce/audio/audio.h       | 128 +++
> drivers/staging/apple-bce/audio/description.h |  45 ++
> drivers/staging/apple-bce/audio/pcm.c         | 311 +++++++
> drivers/staging/apple-bce/audio/pcm.h         |  19 +
> drivers/staging/apple-bce/audio/protocol.c    | 350 ++++++++
> drivers/staging/apple-bce/audio/protocol.h    | 148 ++++
> .../staging/apple-bce/audio/protocol_bce.c    | 229 ++++++
> .../staging/apple-bce/audio/protocol_bce.h    |  75 ++
> drivers/staging/apple-bce/mailbox.c           | 154 ++++
> drivers/staging/apple-bce/mailbox.h           |  56 ++
> drivers/staging/apple-bce/queue.c             | 393 +++++++++
> drivers/staging/apple-bce/queue.h             | 180 +++++
> drivers/staging/apple-bce/queue_dma.c         | 223 +++++
> drivers/staging/apple-bce/queue_dma.h         |  53 ++
> drivers/staging/apple-bce/vhci/command.h      | 207 +++++
> drivers/staging/apple-bce/vhci/queue.c        | 271 +++++++
> drivers/staging/apple-bce/vhci/queue.h        |  79 ++
> drivers/staging/apple-bce/vhci/transfer.c     | 664 +++++++++++++++
> drivers/staging/apple-bce/vhci/transfer.h     |  76 ++
> drivers/staging/apple-bce/vhci/vhci.c         | 764 ++++++++++++++++++
> drivers/staging/apple-bce/vhci/vhci.h         |  55 ++
> 28 files changed, 5735 insertions(+)

I'm slightly puzzled why this was sent to the IOMMU maintainers when it 
doesn't touch any IOMMU code, nor even contain any reference to the 
IOMMU API at all...

Since I don't know enough about audio or USB code, all I can really say 
here is to echo Greg's comment that, judging by that diffstat alone, 
this probably wants to be at least 3-5 separate patches, adding each 
functional piece in manageable chunks.

Thanks,
Robin.