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From: Russell King - ARM Linux <linux@arm.linux.org.uk>
To: Takashi Iwai <tiwai@suse.de>
Cc: Fabio Estevam <fabio.estevam@freescale.com>,
	alsa-devel@alsa-project.org, dri-devel@lists.freedesktop.org,
	Jaroslav Kysela <perex@perex.cz>, Mark Brown <broonie@kernel.org>,
	Yakir Yang <ykk@rock-chips.com>,
	linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH RFC v2 10/13] sound/core: add DRM ELD helper
Date: Sun, 5 Apr 2015 18:26:08 +0100
Message-ID: <20150405172608.GA12732@n2100.arm.linux.org.uk> (raw)
In-Reply-To: <s5h4mouy14a.wl-tiwai@suse.de>

On Sun, Apr 05, 2015 at 06:46:13PM +0200, Takashi Iwai wrote:
> At Sun, 5 Apr 2015 17:20:34 +0100,
> Russell King - ARM Linux wrote:
> > Since (afaik) ALSA has a lack of support for dynamic reconfiguration
> > according to the attached device changing, the best we can do without
> > a huge amount of re-work of HDMI support across all adapters is to
> > process the capabilities of the attached device at prepare time
> > according to the current capabilities.
> 
> Yeah, reconfiguration is tricky.  BTW, how is the HDMI unplug handled
> during playback?

We don't handle it right now - and we don't have any notification to
the audio drivers that that has happened.  Even if we did have such a
notification, I'm not sure what the audio driver could do with it at
the moment.

> > Implementing dynamic reconfiguration in ALSA is not something I want to
> > get involved with, and as we /already/ have HDMI support merged in the
> > kernel, this is not a blocker for at least trying to get some semblence
> > of sanity, rather than having every driver re-implementing stuff like
> > this.
> 
> Well, I didn't mean about the dynamic reconfiguration.  I thought of
> rather min/max pairs, but it was just a wrong assumption.  Scratch
> it.
> 
> One another question: don't we need to deal with the sample bits in
> sad[2]?

It should, but I'm very wary about doing that without seeing more
examples of real SADs.  Right now, all my examples only support
one SAD with either 2 channel or 6 channel audio at the standard
(basic) 32, 44.1 and 48kHz rates.

The HDMI / CEA specs are very loose in their wording about the
short audio descriptors.  I've no idea whether a sink can provide
(for example) descriptors such as:

	LPCM, 6 channel 32, 44.1, 48kHz
	LPCM, 2 channel, 32, 44.1, 48, 96, 192kHz

or whether have to describe that as a single descriptor.  I only
have two TVs to test with here.

What I'm concerned about is that when the ALSA parameter refining
starts, we start with (eg) 2-8 channels, 32-192kHz.  Given that,
if we invoke the channel restriction before the rate restriction,
we would end up limiting to 2 channel at 32-192kHz.  If we apply
the restrictions in the opposite order, we'd restrict to 6
channel, 32-48kHz.  Neither are obviously correct in this
circumstance, and I don't really see a way to solve it given my
understanding of the way ALSA's parameter refinement works.

I suspect this is why most HDMI drivers are implemented such that
they take the maximum capabilities over all SADs, which would end
up restricting audio in the above case to: up to 6 channels, at
32, 44.1, 48, 96 and 192kHz, even though 6 channel @ 192kHz isn't
hasn't been indicated as supported.

Most of this is speculation though, based off what is in the
documentation.  As I say, I don't have enough real-world examples
to get a feel for what manufacturers _actually_ do to give a hint
as to how the documentation should be interpreted.

So, maybe I should just copy what everyone else does and take the
maximum of all descriptors...

-- 
FTTC broadband for 0.8mile line: currently at 10.5Mbps down 400kbps up
according to speedtest.net.
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  reply index

Thread overview: 74+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-04-02  9:20 [RFC v2 0/13] dw_hdmi cleanups, audio preparation, helpers and ahb audio support Russell King - ARM Linux
2015-04-02  9:21 ` [PATCH RFC v2 01/13] drm: imx/dw_hdmi: move phy comments Russell King
2015-04-02  9:21 ` [PATCH RFC v2 02/13] drm: bridge/dw_hdmi: clean up phy configuration Russell King
2015-04-02  9:21 ` [PATCH RFC v2 03/13] drm: bridge/dw_hdmi: clean up hdmi_set_clk_regenerator() Russell King
2015-04-02  9:21 ` [PATCH RFC v2 04/13] drm: bridge/dw_hdmi: use drm_hdmi_avi_infoframe_from_display_mode() Russell King
2015-04-02  9:21 ` [PATCH RFC v2 05/13] drm: bridge/dw_hdmi: simplify hdmi_config_AVI() a little Russell King
2015-04-02  9:21 ` [PATCH RFC v2 06/13] drm: bridge/dw_hdmi: remove mhsyncpolarity/mvsyncpolarity/minterlaced Russell King
2015-04-02  9:21 ` [PATCH RFC v2 07/13] drm: bridge/dw_hdmi: introduce interface to setting sample rate Russell King
2015-04-02  9:21 ` [PATCH RFC v2 08/13] drm: bridge/dw_hdmi: introduce interfaces to enable and disable audio Russell King
2015-04-02  9:22 ` [PATCH RFC v2 09/13] drm/edid: add function to help find SADs Russell King
2015-04-02  9:22 ` [PATCH RFC v2 10/13] sound/core: add DRM ELD helper Russell King
2015-04-05 15:57   ` Takashi Iwai
2015-04-05 16:20     ` Russell King - ARM Linux
2015-04-05 16:46       ` Takashi Iwai
2015-04-05 17:26         ` Russell King - ARM Linux [this message]
2015-05-06 17:02           ` Anssi Hannula
2015-05-07 10:41             ` Russell King - ARM Linux
2015-05-07 11:11               ` Lars-Peter Clausen
2015-05-08 10:56           ` [alsa-devel] " Jyri Sarha
2015-05-08 11:42             ` Russell King - ARM Linux
2015-05-05 22:35     ` Mark Brown
2015-05-06  8:58       ` Liam Girdwood
2015-05-08 13:16   ` [alsa-devel] " Jyri Sarha
2015-05-08 13:27     ` Russell King - ARM Linux
2015-05-08 13:37       ` Jyri Sarha
2015-04-02  9:22 ` [PATCH RFC v2 11/13] sound/core: add IEC958 channel status helper Russell King
2015-04-02  9:22 ` [PATCH RFC v2 12/13] drm: bridge/dw_hdmi-ahb-audio: add audio driver Russell King
2015-04-02  9:22 ` [PATCH RFC v2 13/13] drm: bridge/dw_hdmi-ahb-audio: parse ELD from HDMI driver Russell King
2015-05-09 10:25 ` [PATCH v3 0/13] dw_hdmi cleanups, audio preparation, helpers and ahb audio support Russell King - ARM Linux
2015-05-09 10:25   ` [PATCH 01/13] drm: imx/dw_hdmi: move phy comments Russell King
2015-05-09 10:26   ` [PATCH 02/13] drm: bridge/dw_hdmi: clean up phy configuration Russell King
2015-05-22 15:19     ` Yakir
2015-05-09 10:26   ` [PATCH 03/13] drm: bridge/dw_hdmi: clean up hdmi_set_clk_regenerator() Russell King
2015-05-22 15:22     ` Yakir
2015-05-09 10:26   ` [PATCH 04/13] drm: bridge/dw_hdmi: use drm_hdmi_avi_infoframe_from_display_mode() Russell King
2015-05-09 10:26   ` [PATCH 05/13] drm: bridge/dw_hdmi: simplify hdmi_config_AVI() a little Russell King
2015-05-09 10:26   ` [PATCH 06/13] drm: bridge/dw_hdmi: remove mhsyncpolarity/mvsyncpolarity/minterlaced Russell King
2015-05-09 10:26   ` [PATCH 07/13] drm: bridge/dw_hdmi: introduce interface to setting sample rate Russell King
2015-05-22 15:26     ` Yakir
2015-05-09 10:26   ` [PATCH 08/13] drm: bridge/dw_hdmi: introduce interfaces to enable and disable audio Russell King
2015-05-22 15:28     ` Yakir
2015-05-09 10:26   ` [PATCH 09/13] drm/edid: add function to help find SADs Russell King
2015-05-09 10:26   ` [PATCH 10/13] sound/core: add DRM ELD helper Russell King
2015-05-22 12:20     ` [alsa-devel] " Mark Brown
2015-05-22 13:15       ` Russell King - ARM Linux
2015-05-22 13:30         ` Takashi Iwai
2015-05-22 13:53           ` Russell King - ARM Linux
2015-05-22 13:54             ` Takashi Iwai
2015-05-22 14:00               ` Russell King - ARM Linux
2015-05-22 14:02                 ` Takashi Iwai
2015-05-22 14:05                   ` Takashi Iwai
2015-05-22 16:12                     ` Russell King - ARM Linux
2015-05-09 10:26   ` [PATCH 11/13] sound/core: add IEC958 channel status helper Russell King
2015-05-22 12:40     ` Mark Brown
2015-05-09 10:26   ` [PATCH 12/13] drm: bridge/dw_hdmi-ahb-audio: add audio driver Russell King
2015-05-09 16:49     ` [alsa-devel] " Anssi Hannula
2015-05-09 16:55       ` Russell King - ARM Linux
2015-05-09 17:07         ` Anssi Hannula
2015-05-09 17:40           ` Russell King - ARM Linux
2015-05-09 17:53             ` Russell King - ARM Linux
2015-05-09 17:55             ` Anssi Hannula
2015-05-09 18:11               ` Russell King - ARM Linux
2015-05-10 18:59                 ` Anssi Hannula
2015-05-10 19:33                   ` Russell King - ARM Linux
2015-05-10 20:47                     ` Anssi Hannula
2015-05-11 15:58                     ` Mark Brown
2015-05-09 10:26   ` [PATCH 13/13] drm: bridge/dw_hdmi-ahb-audio: parse ELD from HDMI driver Russell King
2015-05-27 10:43     ` Daniel Vetter
2015-05-27 11:43       ` Mark Brown
2015-05-27 17:31       ` Russell King - ARM Linux
2015-05-27 21:29         ` Daniel Vetter
2015-05-27 21:44           ` Russell King - ARM Linux
2015-05-28  6:43             ` Daniel Vetter
2015-05-28  4:56         ` [alsa-devel] " Takashi Iwai

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