linux-kernel - Re: [alsa-devel] [PATCH V2 06/10] ASoC: img: Add driver for parallel output controller

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Date:	Thu, 22 Oct 2015 20:21:03 +0100
From:	Damien Horsley <Damien.Horsley@...tec.com>
To:	Mark Brown <broonie@...nel.org>
CC:	<alsa-devel@...a-project.org>,
	James Hartley <James.Hartley@...tec.com>,
	Rob Herring <robh+dt@...nel.org>,
	Pawel Moll <pawel.moll@....com>,
	"Mark Rutland" <mark.rutland@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>,
	Liam Girdwood <lgirdwood@...il.com>,
	Jaroslav Kysela <perex@...ex.cz>,
	Takashi Iwai <tiwai@...e.com>, <devicetree@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [alsa-devel] [PATCH V2 06/10] ASoC: img: Add driver for parallel
 output controller

On 19/10/15 19:07, Mark Brown wrote:
> On Mon, Oct 12, 2015 at 01:40:33PM +0100, Damien Horsley wrote:
> 
>> +	spin_lock_irqsave(&prl->lock, flags);
>> +	reg = img_prl_out_readl(prl, IMG_PRL_OUT_CTL);
>> +	ucontrol->value.integer.value[0] = !!(reg & IMG_PRL_OUT_CTL_EDGE_MASK);
>> +	spin_unlock_irqrestore(&prl->lock, flags);
> 
> Do you need to lock a single register read?
>

Between the calls to reset_control_assert and reset_control_deassert,
the block is held in reset. During this time, no register access will
succeed. All register access that may occur concurrently with the reset
needs to be locked

>> +static struct snd_kcontrol_new img_prl_out_controls[] = {
>> +	{
>> +		.iface = SNDRV_CTL_ELEM_IFACE_PCM,
>> +		.name = "Parallel Out Edge Falling",
>> +		.info = img_prl_out_edge_info,
>> +		.get = img_prl_out_get_edge,
>> +		.put = img_prl_out_set_edge
>> +	}
>> +};
> 
> If this is a boolean control (it looked like one) it should be called
> Switch but it's not clear to me what exactly is being controlled here or
> why it's something that should be exposed to userspace.
> 

This controls the edge (rising/falling) of the frame clock that the
samples are generated on. Should I create a set_fmt function and use
SND_SOC_DAIFMT_NB_NF / SND_SOC_DAIFMT_NB_IF to set this instead? I
wasn't sure if those formats were just for I2S or not

>> +	switch (cmd) {
>> +	case SNDRV_PCM_TRIGGER_START:
>> +	case SNDRV_PCM_TRIGGER_RESUME:
>> +	case SNDRV_PCM_TRIGGER_PAUSE_RELEASE:
>> +		reg = img_prl_out_readl(prl, IMG_PRL_OUT_CTL);
>> +		reg |= IMG_PRL_OUT_CTL_ME_MASK;
>> +		img_prl_out_writel(prl, reg, IMG_PRL_OUT_CTL);
>> +		prl->active = true;
>> +		break;
>> +	case SNDRV_PCM_TRIGGER_STOP:
>> +	case SNDRV_PCM_TRIGGER_SUSPEND:
>> +	case SNDRV_PCM_TRIGGER_PAUSE_PUSH:
>> +		img_prl_out_reset(prl);
>> +		prl->active = false;
>> +		break;
> 
> No need for locking on the reset (and doesn't this mean that the control
> state is going to be changed underneath userspace)?
> 

The reset function restores the setting after the reset
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