On 20/05/2014 16:57, Thierry Reding wrote:
On Tue, May 20, 2014 at 04:45:56PM +0200, Daniel Vetter wrote:
>On Tue, May 20, 2014 at 4:29 PM, Imre Deak<imre.deak@xxxxxxxxx> wrote:
> >On Tue, 2014-05-20 at 05:52 +0300, Lin, Mengdong wrote:
> >>This RFC is based on previous discussion to set up a generic
> >>communication channel between display and audio driver and
> >>an internal design of Intel MCG/VPG HDMI audio driver. It's still an
> >>initial draft and your advice would be appreciated
> >>to improve the design.
> >>
> >>The basic idea is to create a new avsink module and let both drm and
> >>alsa depend on it.
> >>This new module provides a framework and APIs for synchronization
> >>between the display and audio driver.
> >>
> >>1. Display/Audio Client
> >>
> >>The avsink core provides APIs to create, register and lookup a
> >>display/audio client.
> >>A specific display driver (eg. i915) or audio driver (eg. HD-Audio
> >>driver) can create a client, add some resources
> >>objects (shared power wells, display outputs, and audio inputs,
> >>register ops) to the client, and then register this
> >>client to avisink core. The peer driver can look up a registered
> >>client by a name or type, or both. If a client gives
> >>a valid peer client name on registration, avsink core will bind the
> >>two clients as peer for each other. And we
> >>expect a display client and an audio client to be peers for each other
> >>in a system.
> >
> >One problem we have at the moment is the order of calling the system
> >suspend/resume handlers of the display driver wrt. that of the audio
> >driver. Since the power well control is part of the display HW block, we
> >need to run the display driver's resume handler first, initialize the
> >HW, and only then let the audio driver's resume handler run. For similar
> >reasons we have to call the audio suspend handler first and only then
> >the display driver resume handler. Currently we solve this using the
> >display driver's late/early suspend/resume hooks, but we'd need a more
> >robust solution.
> >
> >This seems to be a similar issue to the load time ordering problem that
> >you describe later. Having a real device for avsync that would be a
> >child of the display device would solve the ordering issue in both
> >cases. I admit I haven't looked into it if this is feasible, but I would
> >like to see some solution to this as part of the plan.
>
>Yeah, this is a big reason why I want real devices - we have piles of
>infrastructure to solve these ordering issues as soon as there's a
>struct device around. If we don't use that, we need to reinvent all
>those wheels ourselves.
To make the driver core's magic work I think you'd need to find a way to
reparent the audio device under the display device. Presumably they come
from two different parts of the device tree (two different PCI devices I
would guess for Intel, two different platform devices on SoCs). Changing
the parent after a device has been registered doesn't work as far as I
know. But even assuming that would work, I have trouble imagining what
the implications would be on the rest of the driver model.
I faced similar problems with the Tegra DRM driver, and the only way I
can see to make this kind of interaction between devices work is by
tacking on an extra layer outside the core driver model.
That's why we need a new avsink device which is a proper child of the
gfx device, and the audio driver needs to use the componentized device
framework so that the suspend/resume ordering works correctly. Or at
least that's been my idea, might be we have some small gaps here and there.
-Daniel
Intel Semiconductor AG
Registered No. 020.30.913.786-7
Registered Office: Badenerstrasse 549, 8048 Zurich, Switzerland
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