Re: [PATCH 0/5] sanitize hda/i915 interface using the component fw

[Takashi Iwai <tiwai@suse.de>]

At Tue, 09 Dec 2014 18:56:07 +0200,
Imre Deak wrote:
> 
> On Tue, 2014-12-09 at 11:03 +0100, Daniel Vetter wrote:
> > On Tue, Dec 09, 2014 at 10:59:54AM +0200, Imre Deak wrote:
> > > On Mon, 2014-12-08 at 21:14 +0100, Daniel Vetter wrote:
> > > > On Mon, Dec 08, 2014 at 06:42:04PM +0200, Imre Deak wrote:
> > > > > The current hda/i915 interface to enable/disable power wells and query
> > > > > the CD clock rate is based on looking up the relevant i915 module
> > > > > symbols from the hda driver. By using the component framework we can get
> > > > > rid of some global state tracking in the i915 driver and pave the way to
> > > > > fully decouple the two drivers: once support is added to enable/disable
> > > > > the HDMI functionality dynamically in the hda driver, it can bind/unbind
> > > > > itself from the i915 component master, without the need to keep a
> > > > > reference on the i915 module.
> > > > > 
> > > > > This also gets rid of the problem that currently the i915 driver exposes
> > > > > the interface only on HSW and BDW, while it's also needed at least on
> > > > > VLV/CHV.
> > > > 
> > > > Awesome that you're tackling this, really happy to see these hacks go.
> > > > Unfortunately I think it's upside down: hda should be the component master
> > > > and i915 should only register a component.
> > > > 
> > > > Longer story: The main reason for the component helpers is to be able to
> > > > magically delay registering the main/master driver until all the
> > > > components are loaded. Otherwise -EDEFER doesn't work and also the
> > > > suspend/resume ordering this should result in. Master here means whatever
> > > > userspace eventually sees as a device node or similar, component is
> > > > anything really that this userspace interfaces needs to function
> > > > correctly.
> > > 
> > > EDEFER doesn't solve the suspend/resume ordering, at least not in the
> > > general async s/r case. In any case I don't see a problem in making the
> > > hda component the master and I think it's more logical that way as you
> > > said, so I changed that.
> > 
> > Yeah for full async s/r we're screwed as-is. But see below for some crazy
> > ideas.
> > > > I think what we need here is then:
> > > > - Put the current azx_probe into the master_bind callback. The new
> > > >   azx_probe will do nothing else than register the master component and
> > > >   the component match list. To do so it checks the chip flag and if it
> > > >   needs to cooperate with i915 it registers one component match for that.
> > > >   The master_bind (old probe) function calls component_bind_all with the
> > > >   hda_intel pointer as void *data parameter.
> > > 
> > > I'm not sure this is the best way since by this the i915 module would
> > > need to be pinned even when no HDMI functionality is used. I think a
> > > better way would be to let the probe function run as now and
> > > init/register all the non-HDMI functionality. Then only the HDMI
> > > functionality would be inited/registered from the bind/unbind hooks.
> > 
> > Hm, I wasn't sure whether alsa allows this and thought we need i915 anyway
> > to be able to load the driver. But if we can defer just the hdmi part.
> > 
> > > But we could go either way even as a follow-up to this patchset.
> > > 
> > > > - i915 registers a component for the i915 gfx device. It uses the
> > > >   component device to get at i915 sturctures and fills the dev+ops into
> > > >   the hda_intel pointer it gets as void *data.
> > > >
> > > > Stuff we then should do on top:
> > > > - Add deferred probing to azx_probe: Only when all components are there
> > > >   should it actually register. This will take care of all the module load
> > > >   order mess.
> > > 
> > > I agree that we should only register user interfaces when everything is
> > > in place. But I'm not sure deferred probe is the best, we could do
> > > without it by registering HDMI from the component bind hook.
> > 
> > It's mostly a question whether alsa does support delayed addition of
> > interface parts. DRM most definitely does not (except for recently added
> > dp mst connector hotplug). But I guess if the current driver already
> > delays registering the hdmi part then we're fine. I'm not sure about
> > whether it's really safe - I spotted not a lot of locking really to make
> > sure there's no races between i915 loading and userspace trying to access
> > the hdmi side.
> 
> Ok, I'm not sure either. If that's not possible, I agree EDEFER would be
> the best and with that we could also get rid of the request_module() we
> need now.

The probe of HD-audio driver is done in a work anyway, so changing the
code to sync with component should be feasible. 

I'm off today (and yesterday was a Christmas party :), so had little
time for review so far.  Will check the series tomorrow.


thanks,

Takashi
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