[alsa-devel] [PATCH v4 1/7] ASoC: hda - add ASoC HDA codec match function

[Takashi Iwai]

At Thu, 28 May 2015 20:53:59 +0100,
Mark Brown wrote:
> 
> On Wed, May 27, 2015 at 09:17:27PM +0200, Takashi Iwai wrote:
> > Mark Brown wrote:
> 
> > > I'm unclear how that would (practically speaking) be accomplished if
> > > they're in two separate worlds for matching.  Come to think of it how
> > > does this work if we have more than one matching system in use - how
> > > does the driver model code cope with that, what happens if one match
> > > function ends up looking at data for another match type?
> 
> > The matching function does the same thing, but it just looks at the
> > different embedded id tables.  The bus match function already checks
> > each device/driver type beforehand.
> 
> How do we safely do the looking at different tables bit though?  I
> should probably go back and look again at the original patch...

There is the device type check in hda_bus_match() before calling
hda_driver->match(), so it must be safe.  But as already mentioned,
the match isn't the thing to worry too much, as it'll be unified
sooner or later.  The rest (still unseen) stuff is more worrisome.

> > > > The fact you might be missing from the beginning of the story is that
> > > > we need to implement two different driver sets for ASoC, both for
> > > > controller and codec drivers.  They can't be unified with legacy HDA
> > > > unless we merge ASoC core codes into ALSA core (e.g. DPCM or DAPM into
> > > > ALSA core).  Also ASoC has the different ways of registration, too.
> > > 
> > > Wow, that's not what I'd have expected to be happening at all and really
> > > should have been mentioned at some point.  I need to think about this
> > > further.
> 
> > > What I had expected to see for ASoC/HDA integration was something where
> > > ASoC devices were providing a standard HDA controller and then use the
> > > same CODEC drivers as everything else.  Not doing that means that we
> > > inveitably have some duplication for at least things like CODEC quirks
> > > and device specific support which doesn't seem like the best idea.
> > > There's also userspace interfaces for things like the HDA device graph
> > > that'd need looking at.
> 
> > Actually that's the exact plan -- the codec graph will be parsed in
> > user-space (or pre-parsed) and mapped via DFW.
> 
> OK, more surprises!
> 
> Looking at the Broadwell based I2S systems that don't work with any
> released set of upstream software (they need alsa-lib from git) I'm
> wondering how close these systems are to getting into the hands of users
> and what the transition from existing HDA to userspace parsing HDA is
> going to look like.
> 
> I guess older distros will just bind the existing HDA controller drivers
> to them and use the hardware without any of the shiny new features which
> ought to be fine and I'm sure that once everyone has got the new stuff
> it will all be glorious, it's the space where people are upgrading
> (possibly upgrading the kernel or userspace separately) that worries me.
> Especially the bit where people ask me to make their sound work when
> they see their system uses ASoC!

Right, the time is still a question.  Vinod and Liam can answer at
best.

And it's the reason I suggested for pending merge until the codec side
is ready.  We need the topology stuff merged at first, then HDA-codec
driver together with user-space side.

> > The quirks are still open questions.  Currently, ASoC HDA is targeted
> > only to the new systems with SKL.  The rest will keep supported by the
> > existing driver.  So, we expect that the amount of quirks can be
> > reduced much (starting from zero).
> 
> I'm sure that our hardware engineering colleagues wouldn't want us to be
> bored and will give us something to do there :)

I have no doubt about it, too :)

> > > Having HDA use ASoC doesn't seem like a terrible idea, there are aspects
> > > of HDA that map quite well onto ASoC, but doesn't seem to be the
> > > intention here and I'm ambivalent about it being worth the effort.  I
> > > don't think it would need us to move ASoC into the core any more than
> > > any other driver, it'd just make it much more widely used.
> 
> > Heh, that's the very reason why we started implementing a different
> > driver set, after all.  The new driver code is written in minimalistic
> > manner to fit better with ASoC.  The heavy part has been already
> > shifted into HDA core side, that is basically a stripped version from
> > the old HDA code.
> 
> > ASoC implementation was requested rather due to DPCM, compress
> > support, etc, which is currently ASoC-specific features.  The current
> > patchset we've seen is really a tip of iceberg...
> 
> Right, and I'm aware of the reuse potential with sharing features with
> the embedded side (like we're already seeing with the I2S Broadwells) so
> if we don't integrate the two somehow we end up with duplicated drivers
> which would be sad.  It's just that I'd anticipated that this would be
> being handled by black boxing the HDA part of the system from the ASoC
> point of view.

Yes, blackboxing the existing HDA was the first plan.  But it has
obvious drawbacks when joined to ASoC (inheriting a huge amount of
quirks, different designs; HDA legacy is very self-contained, does
DAPM-like path controls and jack-retasking by itself, etc).

Potentially it's still possible to implement in that way, as a plan B,
if a cleaner implementation from scratch fails.  Let's see...


Takashi