Using net/wan/hdlc with serdev

Using net/wan/hdlc with serdev

[Ayush Singh]

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Hello everyone. I have a serdev driver that communicates with a 
coprocessor using HDLC [1]. I am currently using my own HDLC 
implementation, but someone pointed out to me that I might be able to 
use `drivers/net/wan/hdlc` instead.

However, I am not quite sure how I am supposed to use it. I think I am 
supposed to `register_hdlc_protocol` in the serdev probe. The 
`hdlc_proto->netif_rx` callback is called when data is available, and 
`hdlc_proto->xmit` is called to send data? What is the format of 
`skb-data` in rx?

It would be great if someone could point me to some drivers that use 
Linux internal HDLC implementation.


Ayush Singh


[1]: 
https://git.beagleboard.org/gsoc/greybus/beagleplay-greybus-driver/-/tree/develop

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Re: Using net/wan/hdlc with serdev

[Ayush Singh]

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So after some more looking around in the code, I think the workflow is 
quite a bit different than what I thought in the previous mail. I think 
I am supposed to allocate hdlc device using `alloc_hdlcdev` in the 
`serdev->probe` and then implementing `hdlc->xmit` to send data over UART.

But well, I am not sure how to create an HDLC frame? Is there a helper 
that creates HDLC frame skbuff for me? Or maybe the hdlc implementation 
is simply not designed to be used for Asynchronous framing [1]. It would 
be great if someone could explain how to use this HDLC module or point 
to some resource I might have missed.


Ayush Singh


[1]: 
https://en.wikipedia.org/wiki/High-Level_Data_Link_Control#Asynchronous_framing

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Re: Using net/wan/hdlc with serdev

[Bjørn Mork]

Ayush Singh <ayushdevel1325@gmail.com> writes:

> But well, I am not sure how to create an HDLC frame? Is there a helper
> that creates HDLC frame skbuff for me? Or maybe the hdlc
> implementation is simply not designed to be used for Asynchronous
> framing [1]. It would be great if someone could explain how to use
> this HDLC module or point to some resource I might have missed.

I don't know anything at all about this subject, but I believe the wan
HDLC stuff is sync only.

Noting that the ppp driver does all the async framing internally. And
interleaved with ppp specific stuff, so probably not re-usable even if
exported. Ref ppp_async_encode() in drivers/net/ppp/ppp_async.c

I assume it would have used a shared implementation if there was one.
But I could be wrong...


Bjørn

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