Re: [PATCH v8 3/4] gpio: rpmsg: add generic rpmsg GPIO driver

[Andrew Lunn <andrew@lunn.ch>]

> > +	u8 id;		/* Message ID Code */
> > +	u8 vendor;	/* Vendor ID number */
> 
> Does this fields above are mandatory, seems that it is just some constant
> values that are useless.
> 
> > +	u8 version;	/* Vendor-specific version number */
> 
> Why it is vendor specific? the version should represent the rpmsg-tty
> protocol version.
> 
> > +	u8 type;	/* Message type */
> > +	u8 cmd;		/* Command code */
> > +	u8 reserved[5];
> 
> What is the purpose of this reserved field?

They have an implementation of the other end running on there systems,
and it sounds like it is widely deployed, and they are trying to keep
backwards compatibility. The protocol also implements more than
GPIO. There is also I2C, maybe watchdog, i don't remember, but early
versions of this patchset had a list. Some of these fields are used
for some of these other devices.

I've been arguing it should be a clean design, with the protocol
focusing on GPIO. And that the rpmsg channel makes it clear this is a
GPIO device, the protocol itself does not need to include fields to
differentiate between GPIO, I2C etc.

When they start submitting I2C over rpmsg, i expect the same sort of
discussion will start again, so the likelihood of keeping backwards
compatible with there firmware seems low to me.

	   Andrew