Re: [PATCH v2 00/14] greybus: introduce CPC as transport layer

["Jérôme Pouiller" <jerome.pouiller@silabs.com>]

On Thursday 15 January 2026 16:57:53 Central European Standard Time Damien Riégel wrote:
> 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
> 

I have to review this PR for a while. Sorry for the delay. I should
have provided my feedback for the v1.

For now, the abstract interface seems a bit over-engineered. However,
I assume will make sense once other buses will be added. Globally,
this work looks good to me.

Until now, I was was a bit frustrated Greybus for Zephyr only addresses
devices with network capabilities. I hope to be able to easily expose the
services of my Zephyr devices to my Linux host with this PR.

Beside my small comments:

Reviewed-by: Jérôme Pouiller <jerome.pouiller@silabs.com>

-- 
Jérôme Pouiller