Re: Changing the return value of xxx_attach() from void to int.

[Michael <macallan%netbsd.org@localhost>]

Hello,

On Thu, 23 Jun 2016 16:13:53 +0000
Taylor R Campbell <campbell+netbsd-tech-kern%mumble.net@localhost> wrote:

>    Date: Thu, 23 Jun 2016 19:40:14 +0900
>    From: Masanobu SAITOH <msaitoh%execsw.org@localhost>
> 
>      As you know, the return value of device driver's attach function is void.
>    I've thought that we should change it to int for many years. I believe I'm
>    not the only person.
> 
> Sounds plausible to me.  Can you draft an example of a patch to a
> driver that would usefully use this?  Something to demonstrate how
> many untested code paths we can eliminate by moving conditional logic
> about `device failed to attach' to autoconf instead of copying it in
> drivers.

I dimly remember running into this issue - had to abort attach()ing for
some reason and leave a non-functional device_t hanging in the tree.
A good example would be cold graphics chips that we don't know how to
setup without firmware help ( That is, most of them. Many need things
like memory controller and clocks set up in ways that can not be
reliably probed. Clock chips tend to vary, video memory parameters are
hard coded by BIOS with no good way to even guess them etc. )
Like a PCish graphics card with x86 firmware in something not-a-PC.
These will match() successfully ( since we only look for PCI IDs ) but
can't continue halfway through attach().

have fun
Michael