Re: [RFC PATCH] ASoC: fsl: Add Audio Mixer CPU DAI driver

[Viorel Suman <viorel.suman@nxp.com>]

Hi Nicolin,

Thank you for your feedback, same here - just back from vacation.

On Jo, 2018-12-27 at 01:24 +0800, Nicolin Chen wrote:
> Hi Viorel,
> 
> Sorry for the late response, having been on a long vacation.
> 
> The code looks pretty clean. Just some small concerns/questions
> below.
> 
> On Wed, Dec 19, 2018 at 12:30 AM Viorel Suman <viorel.suman@nxp.com>
> wrote:
> > 
> > 
> > This patch implements Audio Mixer CPU DAI driver for NXP iMX8 SOCs.
> > The Audio Mixer is a on-chip functional module that allows mixing
> > of
> > two audio streams into a single audio stream.
> > 
> > Audio Mixer datasheet is available here:
> > https://www.nxp.com/docs/en/reference-manual/IMX8DQXPRM.pdf
> > 
> > Signed-off-by: Viorel Suman <viorel.suman@nxp.com>
> > ---
> >  .../devicetree/bindings/sound/fsl,amix.txt         |  45 ++
> >  sound/soc/fsl/Kconfig                              |   7 +
> >  sound/soc/fsl/Makefile                             |   3 +
> >  sound/soc/fsl/fsl_amix.c                           | 554
> > +++++++++++++++++++++
> >  sound/soc/fsl/fsl_amix.h                           | 101 ++++
> I aimn't against the naming here, but it seems to be AUDMIX in RM?
> 
> Would it be better to align with that? It's your decision though.

To me "AUDMIX" sounds more like some RTL high level integration module,
I would prefer to keep it as it is if there is no strong reason to 
rename it.

> 
> > 
> > diff --git a/Documentation/devicetree/bindings/sound/fsl,amix.txt
> > b/Documentation/devicetree/bindings/sound/fsl,amix.txt
> > +=================================
> > +  - compatible         : Compatible list, contains "fsl,imx8qm-
> > amix"
> > +
> > +  - reg                        : Offset and length of the register
> > set for the device.
> > +
> > +  - clocks             : Must contain an entry for each entry in
> > clock-names.
> > +
> > +  - clock-names                : Must include the "ipg" for
> > register access.
> > +
> > +  - power-domains      : Must contain the phandle to the AMIX
> > power domain node
> > +
> > +Device driver configuration example:
> > +======================================
> > +  amix: amix@59840000 {
> > +    compatible = "fsl,imx8qm-amix";
> > +    reg = <0x0 0x59840000 0x0 0x10000>;
> > +    clocks = <&clk IMX8QXP_AUD_AMIX_IPG>;
> > +    clock-names = "ipg";
> > +    power-domains = <&pd_amix>;
> > +  };
> From the description of DT and RM, I don't see how it connects to
> SAIs.
> 
> Are they fixed to SAI0 and SAI1 in imx8qm? Wondering if it'd be
> better to have such information in the doc.

Please check chapter "16.1.2.2 Audio Mixer" in RM: it has two dedicated
SAI interfaces, SAI4 and SAI5. Audio Mixer operates on bit clock of one
of these interfaces.

> 
> > 
> > diff --git a/sound/soc/fsl/fsl_amix.c b/sound/soc/fsl/fsl_amix.c
> +static const char
> + *width_sel[] = { "16b", "18b", "20b", "24b", "32b", },
> + *pol_sel[] = { "Positive edge", "Negative edge", },
> [...]
> +static const struct soc_enum fsl_amix_enum[] = {
> +/* FSL_AMIX_CTR enums */
> [...]
> +SOC_ENUM_SINGLE_S(FSL_AMIX_CTR, FSL_AMIX_CTR_OUTWIDTH_SHIFT,
> width_sel),
> +SOC_ENUM_SINGLE_S(FSL_AMIX_CTR, FSL_AMIX_CTR_OUTCKPOL_SHIFT,
> pol_sel),
> 
> Should we handle the width in hw_param()?

The width of AMIX output (mixed) stream may be different than the width
of the input streams, the assumption is that the user may want to
control it from userspace.

> 
> Why do we change pol here? It feels like against set_fmt().

You're right, will remove it in the next version.

> 
> > 
> > +static int fsl_amix_dai_set_fmt(struct snd_soc_dai *dai, unsigned
> > int fmt)
> > +{
> > +       /* For playback the AMIX is slave, and for record is master
> > */
> > +       switch (fmt & SND_SOC_DAIFMT_MASTER_MASK) {
> > +       case SND_SOC_DAIFMT_CBM_CFM:
> > +       case SND_SOC_DAIFMT_CBS_CFS:
> So it's used either for playback or capture only, not both at same
> time?

From IP functional perspective AMIX capture is the result of AMIX
playback - AMIX output represents the resulting mixed audio stream
routed to SAI4 RX signals (bit & frame clocks and data). So once we
have playback on either SAI4 or SAI5 (or both) - we can capture the
AMIX output on SAI4.

I guess it would be nice to send the machine driver as part of this
patchset also - it defines two input SAI interfaces as frontends and
AMIX - as backend. Userspace sees only two SAI interfaces exposed, both
of them having playback enabled, and only SAI4 having capture enabled.

> 
> Thanks
> Nicolin

Thank you,
Viorel