Re: nt: usb: USB_RTL8153_ECM should not default to y

Hi Jakub,

On Fri, Sep 17, 2021 at 9:37 PM Jakub Kicinski [off-list ref] wrote:

On Fri, 17 Sep 2021 21:05:55 +0200 Maciej Żenczykowski wrote:

quoted

quoted

Yeah.. more context here:

https://lore.kernel.org/all/7fd014f2-c9a5-e7ec-f1c6-b3e4bb0f6eb6@samsung.com/ (local)

default !USB_RTL8152 would be my favorite but that probably doesn't
compute in kconfig land. Or perhaps bring back the 'y' but more clearly
mark it as a sub-option of CDCETHER? It's hard to blame people for
expecting drivers to default to n, we should make it clearer that this
is more of a "make driver X support variation Y", 'cause now it sounds
like a completely standalone driver from the Kconfig wording. At least
to a lay person like myself.

I think:
        depends on USB_NET_CDCETHER && (USB_RTL8152 || USB_RTL8152=n)
        default y
accomplished exactly what was wanted.

USB_NET_CDCETHER is a dependency, hence:

USB_NET_CDCETHER=n forces it off - as it should - it's an addon to cdcether.

USB_NET_CDCETHER=m disallows 'y' - module implies addon must be module.

What is the expected behavior if USB_NET_CDCETHER=y, and USB_RTL8152=n?

In that case, the old "default y" made USB_RTL8153_ECM builtin.
That was the issue I was fixing.
If USB_RTL8153_ECM is somewhat critical, perhaps you want
"default m if USB_NET_CDCETHER=m"?

quoted

similarly USB_RTL8152 is a dependency, so it being a module disallows 'y'.
This is desired, because if CDCETHER is builtin, so this addon could
be builtin, then RTL8152 would fail to bind it by default.
ie. CDCETHER=y && RTL8152=m must force RTL8153_ECM != y  (this is the bugfix)

basically the funky 'USB_RTL8152 || USB_RTL8152=n' --> disallows 'y'
iff RTL8152=m

'default y' enables it by default as 'y' if possible, as 'm' if not,
and disables it if impossible.

So I believe this had the exact right default behaviour - and allowed
all the valid options.

Right, it was _technically_ correct but run afoul of the "drivers
should default to 'n'" policy. If it should not be treated as a driver
but more of a feature of an existing driver which user has already
selected we should refine the name of the option to make that clear.

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds