linux-kernel - Re: [PATCH v2 2/3] ASoC: Add codec driver for ST TDA7802

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Date:   Tue, 30 Jul 2019 13:38:25 +0100
From:   Charles Keepax <ckeepax@...nsource.cirrus.com>
To:     Thomas Preston <thomas.preston@...ethink.co.uk>
CC:     Liam Girdwood <lgirdwood@...il.com>,
        Mark Brown <broonie@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Jaroslav Kysela <perex@...ex.cz>,
        Takashi Iwai <tiwai@...e.com>,
        Jerome Brunet <jbrunet@...libre.com>,
        Srinivas Kandagatla <srinivas.kandagatla@...aro.org>,
        Marco Felsch <m.felsch@...gutronix.de>,
        Paul Cercueil <paul@...pouillou.net>,
        Kirill Marinushkin <kmarinushkin@...dec.tech>,
        Cheng-Yi Chiang <cychiang@...omium.org>,
        Kuninori Morimoto <kuninori.morimoto.gx@...esas.com>,
        Vinod Koul <vkoul@...nel.org>,
        Annaliese McDermond <nh6z@...z.net>,
        <alsa-devel@...a-project.org>, <devicetree@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, Patrick Glaser <pglaser@...la.com>,
        Rob Duncan <rduncan@...la.com>, Nate Case <ncase@...la.com>
Subject: Re: [PATCH v2 2/3] ASoC: Add codec driver for ST TDA7802

On Tue, Jul 30, 2019 at 01:09:36PM +0100, Thomas Preston wrote:
> Add an I2C based codec driver for ST TDA7802 amplifier. The amplifier
> supports 4 audio channels but can support up to 16 with multiple
> devices.
> 
> Signed-off-by: Thomas Preston <thomas.preston@...ethink.co.uk>
> Cc: Patrick Glaser <pglaser@...la.com>
> Cc: Rob Duncan <rduncan@...la.com>
> Cc: Nate Case <ncase@...la.com>
> ---
> Changes since v1:
> - Use ALSA kcontrol interface to expose device controls to userland
> 	- Gain
> 	- Channel diagnostic mode
> 	- Impedance efficiency optimiser. I decided against setting this
> 	  as a DT property since it seems like something that can be
> 	  changed on the fly.
> - Add regmap default values
> 	- Channel unmute by default is added in a downstream patch.
> 	- I'm not sure if I should keep this since they're all zero,
> 	  although there are other drivers will all-zero reg_defaults.
> - I believe the "//" style is used for SPDX headers in normal C source files.
>   https://lwn.net/Articles/739183/
> - Drop the "enable" sysfs device attribute.
> - Don't set TDM format using magic numbers.
> - Set sample rate using hw_params.
> - Remove unecessary defines.
> - Use DAPM to handle AMP_ON.
> - Cosmetic fixups
> 
>  sound/soc/codecs/Kconfig   |   6 +
>  sound/soc/codecs/Makefile  |   2 +
>  sound/soc/codecs/tda7802.c | 509 +++++++++++++++++++++++++++++++++++++
>  3 files changed, 517 insertions(+)
>  create mode 100644 sound/soc/codecs/tda7802.c
> 
> +++ b/sound/soc/codecs/tda7802.c
> @@ -0,0 +1,509 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * tda7802.c  --  codec driver for ST TDA7802
> + *
> + * Copyright (C) 2016-2019 Tesla Motors, Inc.
> + */

Better to make the whole comment // see something like
sound/soc/codecs/cs47l35.c for an example.

> +static int tda7802_set_bias_level(struct snd_soc_component *component,
> +		enum snd_soc_bias_level level)
> +{
> +	const struct tda7802_priv *tda7802 =
> +		snd_soc_component_get_drvdata(component);
> +	struct snd_soc_dapm_context *dapm_context =
> +			snd_soc_component_get_dapm(component);
> +	const enum snd_soc_bias_level oldlevel =
> +		snd_soc_dapm_get_bias_level(dapm_context);
> +	int err = 0;
> +
> +	dev_dbg(component->dev, "%s level %d\n", __func__, level);
> +
> +	switch (level) {
> +	case SND_SOC_BIAS_ON:
> +		break;
> +	case SND_SOC_BIAS_PREPARE:
> +		break;
> +	case SND_SOC_BIAS_STANDBY:
> +		err = regulator_enable(tda7802->enable_reg);
> +		if (err < 0) {
> +			dev_err(component->dev, "Could not enable.\n");
> +			return err;
> +		}
> +		dev_dbg(component->dev, "Regulator enabled\n");
> +		msleep(ENABLE_DELAY_MS);
> +
> +		if (oldlevel == SND_SOC_BIAS_OFF) {
> +			dev_dbg(component->dev, "Syncing regcache\n");
> +			err = regcache_sync(component->regmap);
> +			if (err < 0)
> +				dev_err(component->dev,
> +					"Could not sync regcache, %d\n", err);

If your doing a regcache_sync I would probably have expected to
see calls to regcache_cache_only.

If the device needs syncing that implies the hardware registers
have lost state, so there is little point in writing to them
if they are unavailable/about to loose their state.

> +		}
> +		break;
> +	case SND_SOC_BIAS_OFF:
> +		regcache_mark_dirty(component->regmap);
> +		err = regulator_disable(tda7802->enable_reg);
> +		if (err < 0)
> +			dev_err(component->dev, "Could not disable.\n");
> +		break;
> +	}
> +
> +	return err;
> +}

Thanks,
Charles