Re: [PATCH] Fix rtl8187 multicast reception

[Kalle Valo <kvalo@codeaurora.org>]

Nils Holland <nholland@tisys.org> writes:

> On Sun, Feb 19, 2017 at 09:46:16AM +0200, Kalle Valo wrote:
>> Larry Finger <Larry.Finger@lwfinger.net> writes:
>> 
>> > On 02/18/2017 07:35 PM, Nils Holland wrote:
>> >
>> > I would prefer a module parameter that would allow this change to be
>> > implemented only if the user takes special action. I suspect that you
>> > will have no difficulty preparing such a change. If that is not true,
>> > I would be happy to help.
>> 
>> I understand why you prefer having a module parameter but the thing is
>> that being able to receive multicast frames is really basic
>> functionality. We should not hide it under a module parameter.
>
> Well, this is a tough question, I have to admit that I have a somewhat
> weird feeling making a change that also applies to other hardware that
> I cannot test on, so I don't know about any negative consequences that
> might arise there, especially when the change isn't based on some
> official information from some documentation, but rather a result of
> trial & error. So I can fully understand Larry's concerns and do in
> fact think that a module parameter could be a nice solution, so that
> by default the behavior if the driver does not change.

There are lots of hardware variations that cannot be tested when a patch
is commited. If we followed the same methdology with all patches we
would have thousands of module parameters in kernel in no time :)

> From an end-user standpoint, it's probably always worse to see
> something break which has always worked before than it is to have
> something not work properly right from the start, but being able to
> easily find some parameter to fix this.

Sure. But if there's a report about this patch breaking something, it's
easy to revert it.

> On the other hand, use of this particular USB wifi card is probably
> not so common these days so relatively few people would notice at all.
> Tough! I guess I'll submit a module parameter based v2 of the patch
> later today, just as Larry suggested!

Also remember to add a prefix to the title:

https://wireless.wiki.kernel.org/en/developers/documentation/submittingpatches#subject

>> Isn't there any other option, for example does anyone have hw to test
>> this with other hw? (what exactly?) Or maybe we just take the risk and
>> take it as is and revert if problems arise?
>
> Of course, if someone has other hw, more testing would be nice! Any
> situation where the card is supposed to receive multicast frames
> should be suitable as a test case - in my case, just connecting to my
> local network and expecting to see the card pick up RAs and acquire an
> IPv6 address is the easiest test case. This works nicely on several
> other machines with completely different wifi hardware as well as
> wired machines, but fails without the fix on the rtl8187b. It would,
> for example, be interesting to see if a non-b 8187 behaves the same or
> if things work there out of the box.

I'm not familiar with the driver so when you say "non-b 8187" what do
you mean exactly? What kind of hardware are we talking about? How many
different hardware versions are there that this patch affects? Is the
firmware/hardware really so different that the chances are high that
this breaks something?

> In that case, instead of doing a module parameter, I could also change
> the fix so that it only does something different on the b-variants of
> the card and doesn't change behavior at all on non-b.

Now that's much better option than adding a module parameter.

-- 
Kalle Valo