Re: [PATCH v13 3/4] gpio: rpmsg: add generic rpmsg GPIO driver

[Andrew Lunn <andrew@lunn.ch>]

> Remote side learns the endpoint when it receives any message from Linux
> from the dynamic endpoint.
> 
> Lets say rpmsg_create_ept() allocates a dynamic local ept of 1026. When
> you send the message from this endpoint, the standard rpmsg header
> would have:
> 
>     85 struct rpmsg_hdr {
>     86         __rpmsg32 src; // 1026
>     87         __rpmsg32 dst; // rpdev->dst (e.g. 400)
>     88         __rpmsg32 reserved;
>     89         __rpmsg16 len;
>     90         __rpmsg16 flags;
>     91         u8 data[];
>     92 } __packed;
> 
> Remote side tracks the dynamic endpoint by reading src = 1026. And while
> sending the response it fills the header as:

I've never used rpmsg, so this might be a FAQ. How does the remote
side know what the endpoint is to be used for? Here we are talking
about GPIO. But the same hardware implements I2C, and a few other
things. How do we indicate this endpoint is for GPIO?

Maybe also related, this hardware also supports a number of GPIO
controllers. There has been some argument about if one endpoint should
support multiple GPIO controllers. Or, like gpio-virtio, one endpoint
represents one GPIO controller, and you instantiate multiple
endpoints, one per controller. How can you tell the different
instances of GPIO endpoints apart when they are dynamically created?

   Andrew