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Date:   Tue, 10 Mar 2020 09:17:14 +0100
From:   Alex Riesen <alexander.riesen@cetitec.com>
To:     Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
CC:     Laurent Pinchart <laurent.pinchart@ideasonboard.com>,
        Geert Uytterhoeven <geert@linux-m68k.org>,
        Kieran Bingham <kieran.bingham@ideasonboard.com>,
        Mauro Carvalho Chehab <mchehab@kernel.org>,
        Hans Verkuil <hverkuil-cisco@xs4all.nl>,
        Rob Herring <robh+dt@kernel.org>,
        Mark Rutland <mark.rutland@arm.com>,
        Driver Development <devel@driverdev.osuosl.org>,
        Linux Media <linux-media@vger.kernel.org>,
        Linux Kernel <linux-kernel@vger.kernel.org>,
        Device Tree <devicetree@vger.kernel.org>,
        Renesas SoC <linux-renesas-soc@vger.kernel.org>
Subject: Re: [PATCH 8/8] arm64: dts: renesas: salvator: add a connection from
 adv748x codec (HDMI input) to the R-Car SoC
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Mail-Followup-To: Alex Riesen <alexander.riesen@cetitec.com>,
        Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>,
        Laurent Pinchart <laurent.pinchart@ideasonboard.com>,
        Geert Uytterhoeven <geert@linux-m68k.org>,
        Kieran Bingham <kieran.bingham@ideasonboard.com>,
        Mauro Carvalho Chehab <mchehab@kernel.org>,
        Hans Verkuil <hverkuil-cisco@xs4all.nl>,
        Rob Herring <robh+dt@kernel.org>,
        Mark Rutland <mark.rutland@arm.com>,
        Driver Development <devel@driverdev.osuosl.org>,
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        Linux Kernel <linux-kernel@vger.kernel.org>,
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        Renesas SoC <linux-renesas-soc@vger.kernel.org>
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Hello Morimoto-san,

Kuninori Morimoto, Tue, Mar 10, 2020 02:07:23 +0100:
> > Should the adv748x driver also implement anything to configure the frequency
> > of MCLK clock? I mean something like .set_sysclk and .set_fmt callbacks of
> > snd_soc_dai_ops?
> > 
> > Or is the driver implementation, which depends on mclk-fs to be 256, the audio
> > stream format to be 8x S24_LE, and requires strictly 48kHz sampling rate on
> > the HDMI input, a totally acceptable first attempt at writing a DAI driver?
> > 
> > I'm a bit bothered by that, as the hardware is also capable of decoding
> > stereo, sampling rate 32-192kHz, a variety of PCM and compressed/encrypted
> > formats, 128-768fs MCLK multipliers, and a row of I2S options.
> > 
> > I just find it confusing to place the configuration interfaces.
> > For instance, the patches use the media ioctl for audio output selection to
> > select I2S protocol. While works, it does not feel right (shouldn't it be in
> > the device tree?)
> > 
> > Maybe you can point me at a driver doing something similar? I'm studying media
> > drivers now, but not many of them use ASoC interfaces for devices providing a
> > clock. Or maybe I should better look at sound/soc/...?
> 
> Setting Sound Clock for all cases/patterns are very complex and difficult actually.
> (ADV7482 configuration) x (ADG divider / selector) x etc, etc...
> 
> Thus, Current R-Car sound is assuming that audio_clk_a/b/c/i are providing
> route clock (= no configuration, fixed clock), and ADG divides it,
> and provide best clock to each SSIx.
> Current Salvator/ULCB already have 44.1/48kHz route clock (= CS2000 and Audio_CLK_A),
> and we can reuse it for all SSIx. Thus, ADV7482 clock is not necessary, I guess ?
> Or providing specific clock for some case is enough
> (ADG will automatically select it if necessary).

In this particular case, the ADV7482 *must* provide the clock, I believe: it
extracts the audio stream from the HDMI connection (in addition to everything
else) and serves the stream on I2S. Its MCLK line is physically connected to
the CLK_C line (which is an input) of the R-Car SoC. The I2S audio
transmission does not work if the ADV7482 clock is not programmed (or
programmed incorrectly).
Yes, I tried (I also tried programming it incorrectly, just because I didn't
know what I was doing).

> If ADV7482 needs more detail clock settings combination,
> then, there is no method to adjust to it.
> We need to consider such system somehow.

Not encouraging...

Maybe I should leave the clock fixed, with the frequency configuration in the
device tree, e.g. as adv7482 port node property "clock-frequency".
Which feels rather pathetic, but at least serves my purpose (48k, 8x24).

But let me describe the situation as I see it first.

As far as I understand, the SSI4 (Salvator-X board) should be programmed by
the snd-soc-rcar driver in the "slave receiver" mode for this use case, which
is HDMI input ADV7482 (I2S master, TDM) -> SSI4 (I2S slave)):

[   63.305990] asoc_simple_card_parse_clk: asoc-audio-graph-card sound: rsnd-dai.1 : sysclk = 66666664, direction 0
[   63.306028] asoc_simple_card_parse_clk: asoc-audio-graph-card sound: adv748x-i2s : sysclk = 12288000, direction 1

I am a bit bothered by the fact that sysclk of rsnd-dai.1 does not match that
sysclk of adv7482-i2s, but I think it's just DT node configuration.

[   63.306033] asoc_simple_card_set_dailink_name: asoc-audio-graph-card sound: name : rsnd-dai.1-adv748x-i2s
...
[   63.332641] asoc-audio-graph-card sound: adv748x.4-0070 <-> rsnd-dai.1 mapping ok
...
[   63.341317] dapm_connect_dai_link_widgets:  rsnd-dai.1-adv748x-i2s: connected DAI link adv748x.4-0070:Capture -> ec500000.sound:DAI1 Capture
...
[  128.961389] rsnd_write: rcar_sound ec500000.sound: w ssi[4] - SSICR ( 124) : 9ceb0100

Decoding this last line (9ceb0100) gives SSICR.TRMD (bit1) =0, SSICR.SCKD
(bit15) =0, SSICR.SWSD (bit14) =0. The combination is documented as "slave
receiver". Which, I assume, makes SSI4 use the external clock. Given the
received stream looks ok, something also must have set the dividers correctly.

From the above, I conclude, whatever the complexity of the audio system clock
configuration, it seems to be implemented for the case.

I only miss a more or less clear way to configure the I2S master (ADV7482, that is).

Regards,
Alex