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. Thierry
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