linux-kernel - [PATCH v2 00/14] greybus: introduce CPC as transport layer

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Message-ID: <20260115155808.36102-1-damien.riegel@silabs.com>
Date: Thu, 15 Jan 2026 10:57:53 -0500
From: Damien Riégel <damien.riegel@...abs.com>
To: greybus-dev@...ts.linaro.org, Johan Hovold <johan@...nel.org>,
        Alex Elder <elder@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-kernel@...r.kernel.org
Cc: Silicon Labs Kernel Team <linux-devel@...abs.com>,
        Damien Riégel <damien.riegel@...abs.com>
Subject: [PATCH v2 00/14] greybus: introduce CPC as transport layer

Hi,

This patchset brings support for Silicon Labs' CPC protocol as transport
layer for Greybus. This is introduced as a module that sits between
Greybus and CPC Host Device Drivers implementations, like SDIO or SPI.
This patchset includes SDIO as physical layer.

        +----------------------------------------------------+
        |                      Greybus                       |
        +----------------------------------------------------+
                                 /|\
                                  |
                                 \|/
        +----------------------------------------------------+
        |                        CPC                         |
        +----------------------------------------------------+
              /|\                /|\                /|\
               |                  |                  |
              \|/                \|/                \|/
          +----------+       +---------+       +-----------+
          |   SDIO   |       |   SPI   |       |   Others  |
          +----------+       +---------+       +-----------+

CPC implements some of the features of Unipro that Greybus relies upon,
like reliable transmission. CPC takes care of detecting transmission
errors and retransmit frames if necessary, but that feature is not part
of the RFC to keep it concise. There's also a flow-control
feature, preventing sending messages to already full cports.

In order to implement these features, a 4-byte header is prepended to
Greybus messages, making the whole header 12 bytes (Greybus header is 8
bytes).

This RFC starts by implementing a shim layer between physical bus
drivers (like SDIO and SPI) and Greybus, and progressively add more
elements to it to make it useful in its own right. Finally, an SDIO
driver is added to enable the communication with a remote device.


Changes in v2:
  - addressed review comments and errors reported by kernel bot
  - for SDIO driver, remove padding between headers and payloads when
    aggregating packets together

Damien Riégel (13):
  greybus: cpc: add minimal CPC Host Device infrastructure
  greybus: cpc: introduce CPC cport structure
  greybus: cpc: use socket buffers instead of gb_message in TX path
  greybus: cpc: pack cport ID in Greybus header
  greybus: cpc: switch RX path to socket buffers
  greybus: cpc: introduce CPC header structure
  greybus: cpc: account for CPC header size in RX and TX path
  greybus: cpc: add and validate sequence numbers
  greybus: cpc: acknowledge all incoming messages
  greybus: cpc: use holding queue instead of sending out immediately
  greybus: cpc: honour remote's RX window
  greybus: cpc: let host device drivers dequeue TX frames
  greybus: cpc: add private data pointer in CPC Host Device

Gabriel Beaulieu (1):
  greybus: cpc: add CPC SDIO host driver

 MAINTAINERS                    |   6 +
 drivers/greybus/Kconfig        |   2 +
 drivers/greybus/Makefile       |   2 +
 drivers/greybus/cpc/Kconfig    |  22 ++
 drivers/greybus/cpc/Makefile   |   9 +
 drivers/greybus/cpc/cpc.h      |  75 +++++
 drivers/greybus/cpc/cport.c    | 112 +++++++
 drivers/greybus/cpc/header.c   | 136 +++++++++
 drivers/greybus/cpc/header.h   |  55 ++++
 drivers/greybus/cpc/host.c     | 313 +++++++++++++++++++
 drivers/greybus/cpc/host.h     |  63 ++++
 drivers/greybus/cpc/protocol.c | 168 +++++++++++
 drivers/greybus/cpc/sdio.c     | 533 +++++++++++++++++++++++++++++++++
 13 files changed, 1496 insertions(+)
 create mode 100644 drivers/greybus/cpc/Kconfig
 create mode 100644 drivers/greybus/cpc/Makefile
 create mode 100644 drivers/greybus/cpc/cpc.h
 create mode 100644 drivers/greybus/cpc/cport.c
 create mode 100644 drivers/greybus/cpc/header.c
 create mode 100644 drivers/greybus/cpc/header.h
 create mode 100644 drivers/greybus/cpc/host.c
 create mode 100644 drivers/greybus/cpc/host.h
 create mode 100644 drivers/greybus/cpc/protocol.c
 create mode 100644 drivers/greybus/cpc/sdio.c

-- 
2.52.0