On Tue, May 13, 2025 at 05:15:20PM -0400, Damien Riégel wrote:
On Mon May 12, 2025 at 1:07 PM EDT, Andrew Lunn wrote:
On Sun, May 11, 2025 at 09:27:33PM -0400, Damien Riégel wrote:
Hi,
This patchset brings initial support for Silicon Labs CPC protocol, standing for Co-Processor Communication. This protocol is used by the EFR32 Series [1]. These devices offer a variety for radio protocols, such as Bluetooth, Z-Wave, Zigbee [2].
Before we get too deep into the details of the patches, please could you do a compare/contrast to Greybus.
Thank you for the prompt feedback on the RFC. We took a look at Greybus in the past and it didn't seem to fit our needs. One of the main use case that drove the development of CPC was to support WiFi (in coexistence with other radio stacks) over SDIO, and get the maximum throughput possible. We concluded that to achieve this we would need packet aggregation, as sending one frame at a time over SDIO is wasteful, and managing Radio Co-Processor available buffers, as sending frames that the RCP is not able to process would degrade performance.
Greybus don't seem to offer these capabilities. It seems to be more geared towards implementing RPC, where the host would send a command, and then wait for the device to execute it and to respond. For Greybus' protocols that implement some "streaming" features like audio or video capture, the data streams go to an I2S or CSI interface, but it doesn't seem to go through a CPort. So it seems to act as a backbone to connect CPorts together, but high-throughput transfers happen on other types of links. CPC is more about moving data over a physical link, guaranteeing ordered delivery and avoiding unnecessary transmissions if remote doesn't have the resources, it's much lower level than Greybus.
As is said, i don't know Greybus too well. I hope its Maintainers can comment on this.
Also, this patch adds Bluetooth, you talk about Z-Wave and Zigbee. But the EFR32 is a general purpose SoC, with I2C, SPI, PWM, UART. Greybus has support for these, although the code is current in staging. But for staging code, it is actually pretty good.
I agree with you that the EFR32 is a general purpose SoC and exposing all available peripherals would be great, but most customers buy it as an RCP module with one or more radio stacks enabled, and that's the situation we're trying to address. Maybe I introduced a framework with custom bus, drivers and endpoints where it was unnecessary, the goal is not to be super generic but only to support coexistence of our radio stacks.
This leads to my next problem.
https://www.nordicsemi.com/-/media/Software-and-other-downloads/Product-Brie... Nordic Semiconductor has what appears to be a similar device.
https://www.microchip.com/en-us/products/wireless-connectivity/bluetooth-low... Microchip has a similar device as well.
https://www.ti.com/product/CC2674R10 TI has a similar device.
And maybe there are others?
Are we going to get a Silabs CPC, a Nordic CPC, a Microchip CPC, a TI CPC, and an ACME CPC?
How do we end up with one implementation?
Maybe Greybus does not currently support your streaming use case too well, but it is at least vendor neutral. Can it be extended for streaming?
And maybe a dumb question... How do transfers get out of order over SPI and SDIO? If you look at the Open Alliance TC6 specification for Ethernet over SPI, it does not have any issues with ordering.
Andrew