[alsa-devel] [Intel-gfx] Need your advice: Add a new communication inteface between HD-Audio and Gfx drivers for hotplug notification/ELD update

Takashi Iwai tiwai at suse.de
Wed Jan 22 18:23:24 CET 2014

At Wed, 22 Jan 2014 10:45:26 -0500,
Rob Clark wrote:
> On Wed, Jan 22, 2014 at 10:20 AM, Daniel Vetter <daniel at ffwll.ch> wrote:
> > On Wed, Jan 22, 2014 at 10:04:14AM -0500, Rob Clark wrote:
> >> sorry to jump into this a bit late, so maybe this was covered already earlier..
> >
> > It just started, I've quoted everything when cc'ing dri-devel. But good to
> > have examples outside of x86 (where things are mostly standardized by the
> > Eye of Redmond).
> perhaps the arm/SoC stuff was standardized by the Eye of Cthulhu
> btw, added a few other SoC drm types who might be interested in the topic
> >> For drm/msm the hdmi code needs something along these lines from audio:
> >>
> >> int hdmi_audio_info_setup(struct platform_device *pdev, bool enabled,
> >>         uint32_t num_of_channels, uint32_t channel_allocation,
> >>         uint32_t level_shift, bool down_mix);
> >> void hdmi_audio_set_sample_rate(struct platform_device *pdev, int rate);
> >>
> >> (former is mainly to setup avi audio infoframe, latter for clks)
> >>
> >> in addition to hotplug and ELD stuff
> >
> > Can you elaborate a bit on what you need for msm? On intel (and I think
> > the other x86 platforms are similar) we have separate buffers in the hw
> > for avi infoframes and audio infoframes, so the drm and alsa driver can
> > bash the right stuff into the hardware on their own. I'm mostly confused
> > since you say _AVI_ infoframe here, which is purely generated by the drm
> > side of the code here. Or at least that's been my understanding.
> Sorry, typo, meant audio infoframe
> We could have the API such that the audio driver constructs the
> infoframe.. that probably makes more sense and simplifies things.

The HD-audio has a code for doing that, so if needed, it can be copied
from there.  But, even AMD HD-audio codec doesn't use this scheme but
just sets up a few verbs for channel-allocations, etc, so the complete
audio infoframe isn't necessary in most cases, as it seems.

>  But
> the drm driver is the one that needs to bash that constructed buffer
> into the hw.  Or, well, either that or both drivers ioremap the same
> block of registers, but that seems somewhat lame.
> But I do need to know some basic things, like # of channels.. and
> would kinda prefer not to have to parse the audio infoframe to get
> that info.

Yes, it makes things complex.  It's one of the reasons we'd like to
have a more straightforward interface.

> > The clocks are also funny really, but I'm not sure whether this fits. I'd
> > have expected some DT-based generic clock source which the audio driver
> > just grabs as part of his multi-device beast (maybe using Russell's new
> > driver core code) and used directly. What's the reason that this has to go
> > through the drm driverr?
> possibly it could be exposed to the audio driver as a 'struct clk'
> that is implemented/registered/exported by the drm driver, I guess?

Hrm, but I guess this is also purely optional?
I'd like to start rather from a minimum set.

> fwiw, if curious, what I have on msm so far is at:
> https://github.com/freedreno/kernel-msm/commit/6ffd278d39a3ff8712c70b5fd98dc135bd6c7b8a
> It works on downstream qcom android kernel.. the API exported by drm
> driver, called by audio driver, is basically just a clone of the hack
> that was already there between fbdev and alsa.  I haven't tried to
> clean that up at all yet.  It was enough work just untangling ION (!!)
> from alsa in that kernel :-/

Thanks for the pointer!


> BR,
> -R
> > Cheers, Daniel
> > --
> > Daniel Vetter
> > Software Engineer, Intel Corporation
> > +41 (0) 79 365 57 48 - http://blog.ffwll.ch

More information about the Alsa-devel mailing list