linux-kernel - Re: [PATCH v2 3/5] ALSA: cs35l41: Add shared boost feature

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Date:   Wed, 8 Feb 2023 10:09:27 +0000
From:   Charles Keepax <ckeepax@...nsource.cirrus.com>
To:     Lucas Tanure <lucas.tanure@...labora.com>
CC:     David Rhodes <david.rhodes@...rus.com>,
        Liam Girdwood <lgirdwood@...il.com>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Mark Brown <broonie@...nel.org>,
        "Rob Herring" <robh+dt@...nel.org>,
        Jaroslav Kysela <perex@...ex.cz>,
        Takashi Iwai <tiwai@...e.com>, <alsa-devel@...a-project.org>,
        <devicetree@...r.kernel.org>, <patches@...nsource.cirrus.com>,
        <linux-kernel@...r.kernel.org>, <kernel@...labora.com>
Subject: Re: [PATCH v2 3/5] ALSA: cs35l41: Add shared boost feature

On Tue, Feb 07, 2023 at 04:25:24PM +0000, Lucas Tanure wrote:
> Shared boost allows two amplifiers to share a single boost
> circuit by communicating on the MDSYNC bus.
> The passive amplifier does not control the boost and receives
> data from the active amplifier.
> 
> Shared Boost is not supported in HDA Systems.
> Based on David Rhodes shared boost patches.
> 
> Signed-off-by: Lucas Tanure <lucas.tanure@...labora.com>
> ---
> -int cs35l41_global_enable(struct regmap *regmap, enum cs35l41_boost_type b_type, int enable)
> +int cs35l41_global_enable(struct regmap *regmap, enum cs35l41_boost_type b_type, int enable,
> +			  struct completion *pll_lock)
>  {
>  	int ret;
> +	unsigned int gpio1;
>  
>  	switch (b_type) {
> +	case CS35L41_SHD_BOOST_ACTV:
> +	case CS35L41_SHD_BOOST_PASS:
> +		regmap_update_bits(regmap, CS35L41_PWR_CTRL3, CS35L41_SYNC_EN_MASK, 0);
> +
> +		gpio1 = enable ? CS35L41_GPIO1_MDSYNC : CS35L41_GPIO1_HIZ;
> +		regmap_update_bits(regmap, CS35L41_GPIO_PAD_CONTROL, CS35L41_GPIO1_CTRL_MASK,
> +				   gpio1 << CS35L41_GPIO1_CTRL_SHIFT);
> +
> +		ret = regmap_update_bits(regmap, CS35L41_PWR_CTRL1, CS35L41_GLOBAL_EN_MASK,
> +					 enable << CS35L41_GLOBAL_EN_SHIFT);
> +		usleep_range(3000, 3100);
> +		if (!enable)
> +			break;
> +
> +		if (!pll_lock)
> +			return -EINVAL;
> +
> +		ret = wait_for_completion_timeout(pll_lock, msecs_to_jiffies(1000));
> +		if (ret == 0) {
> +			ret = -ETIMEDOUT;
> +		} else {
> +			regmap_update_bits(regmap, CS35L41_PWR_CTRL3, CS35L41_SYNC_EN_MASK, 0);
> +			regmap_update_bits(regmap, CS35L41_PWR_CTRL1, CS35L41_GLOBAL_EN_MASK,
> +								 0 << CS35L41_GLOBAL_EN_SHIFT);
> +			usleep_range(3000, 3100);
> +			regmap_update_bits(regmap, CS35L41_PWR_CTRL1, CS35L41_GLOBAL_EN_MASK,
> +								 1 << CS35L41_GLOBAL_EN_SHIFT);
> +			usleep_range(3000, 3100);
> +		}

This approach also makes me nervous, I was somewhat imagining the
usage of regmap_multi_reg_write for this sequence was because it
was very important that no other register writes could interleave
in between these writes. But I don't know, so it could also have
just been a random design choice. So we probably need David to
confirm if that was the reason for the original code here.

Thanks,
Charles