Re: [PATCH v3 2/7] drm/tinydrm: Add helper functions

[Daniel Vetter]

On Mon, Feb 06, 2017 at 12:08:47PM +0100, Thierry Reding wrote:
> On Mon, Feb 06, 2017 at 11:07:42AM +0100, Daniel Vetter wrote:
> > On Mon, Feb 6, 2017 at 10:35 AM, Thierry Reding <thierry.reding@xxxxxxxxx>
> > wrote:
> > 
> > > > > > +EXPORT_SYMBOL(tinydrm_disable_backlight);
> > > > > > +#endif
> > > > >
> > > > > These look like they really should be part of the backlight subsystem.
> > > I
> > > > > don't see anything DRM specific about them. Well, except for the error
> > > > > messages.
> > > >
> > > > So this is a bit an unpopular opinion with some folks, but I don't
> > > require
> > > > anyone to submit new code to subsystems outside of drm for new drivers.
> > > > Simply because it takes months to get stuff landed, and in general it's
> > > > not worth the trouble.
> > >
> > > "Not worth the trouble" is very subjective. If you look at the Linux
> > > kernel in general, one of the reasons why it works so well is because
> > > the changes we make apply to the kernel as a whole. Yes, sometimes that
> > > makes things more difficult and time-consuming, but it also means that
> > > the end result will be much more widely usable and therefore benefits
> > > everyone else in return. In my opinion that's a large part of why the
> > > kernel is so successful.
> > >
> > > > We have piles of stuff in drm and drm drivers that should be in core but
> > > > isn't.
> > > >
> > > > Imo the only reasonable way is to merge as-is, then follow-up with a
> > > patch
> > > > series to move the helper into the right subsystem. Most often
> > > > unfortunately that follow-up patch series will just die.
> > >
> > > Of course follow-up series die. That's because nobody cares to follow-up
> > > once their code has been merged.
> > >
> > > Collecting our own helpers or variants of subsystems is a great way of
> > > isolating ourselves from the rest of the community. I don't think that's
> > > a good solution in the long run at all.
> > >
> > 
> > We have a bunch of patch series that we resubmit for months and they go
> > exactly nowhere. They don't die because we stop caring, they die because
> > they die. Some of them we even need to constantly rebase and carry around
> > in drm-tip since our CI would Oops or spew WARNIGs all over the place.
> > There's simply some areas of the kernel which seem overloaded under patches
> > and no one is willing or able to fix things, and I can't fix the entire
> > kernel. Nor expect contributors (who have much less political weight to
> > throw around than me) to do that and succeed. And we don't end up with
> > worse code in the drm subsystem, since we can still do the refactoring
> > within drm helpers and end up with clean drivers.
> > 
> > I fully agree that it's not great for the kernel's future, but when I'm
> > stuck with the option to get shit done or burning out playing the
> > upstreaming game, the choice is easy. And in the end I care about open
> > source gfx much more than the kernel, and I think for open source gfx's
> > success it's crucial that we're welcoming to new contributors and don't
> > throw up massive roadblocks. Open source gfx is tiny and still far away
> > from world domination, we need _lots_ more people. If that means routing
> > around other subsystems for them, I'm all for it.
> 
> I can't say I fully agree with that sentiment. I do see how routing
> around subsystems can be useful occasionally. If nobody will merge the
> code, or if nobody cares, then by all means, let's make them DRM-
> specific helpers.
> 
> But I think we need to at least try to do the right thing. If only to
> teach people what the right way is. If we start accepting such things
> by default, how can we expect contributors to even try?
> 
> I also think that contributors will often end up contributing not only
> to DRM but to the kernel as a whole. As such it should be part of our
> mentoring to teach them about how the process works as a rule, even if
> the occasional exception is necessary to get things done.
> 
> In this particular case, I know for a fact that both backlight and SPI
> maintainers are very responsive, so that's not a good excuse.

I definitely don't want that we don't attempt this. But brought from years
of experience, I recommend to merge first (with pre-refactoring already
applied, but helpers only extracted, not yet at the right spot), and then
follow up with. Because on average, there's way too many trees with
overloaded maintainers who maybe look at your patch once per kernel
release cycle.

If you know that backlight and spi isn't one of these areas (anything that
goes through takashi/sound is a similar good experience for us on the i915
side), then I guess we can try. But then Noralf has already written a few
months worth of really great refactoring, and I'm seriously starting to
feel guilty for volunteering him for all of this. Even though he seems to
be really good at it, and seems to not mind, it's getting a bit silly.
Given that I'd say up to Noralf.

In short, there's always a balance.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch