linux-kernel - Re: [alsa-devel][PATCH 2/3] ASoC: fsl_sai: Add support for tdm slots operation

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Message-ID: <20150122062004.GA7046@b50113>
Date:	Thu, 22 Jan 2015 14:20:06 +0800
From:	Zidan Wang <b50113@...escale.com>
To:	Nicolin Chen <nicoleotsuka@...il.com>
CC:	Zidan Wang <zidan.wang@...escale.com>, <timur@...i.org>,
	<Xiubo.Lee@...il.com>, <lgirdwood@...il.com>, <broonie@...nel.org>,
	<perex@...ex.cz>, <tiwai@...e.de>, <alsa-devel@...a-project.org>,
	<linuxppc-dev@...ts.ozlabs.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [alsa-devel][PATCH 2/3] ASoC: fsl_sai: Add support for tdm slots
 operation

On Wed, Jan 21, 2015 at 09:44:10PM -0800, Nicolin Chen wrote:
> On Thu, Jan 22, 2015 at 12:55:35PM +0800, Zidan Wang wrote:
> > On Wed, Jan 21, 2015 at 10:08:03AM -0800, Nicolin Chen wrote:
> > > On Tue, Jan 20, 2015 at 08:21:19PM +0800, Zidan Wang wrote:
> > > > @@ -369,10 +380,25 @@ static int fsl_sai_hw_params(struct snd_pcm_substream *substream,
> > > >  	u32 word_width = snd_pcm_format_width(params_format(params));
> > > >  	u32 val_cr4 = 0, val_cr5 = 0;
> > > >  	int ret;
> > > > +	u32 bclk;
> > > > +
> > > > +	if (channels == 1)
> > > > +		channels = 2;
> > > > +
> > > > +	if (!sai->slots || sai->slots % channels)
> > > > +		sai->slots = channels;
> > > > +
> > > > +	sai->slots = sai->slots / channels;
> > > > +
> > > > +	if (sai->slot_width < word_width || sai->is_dsp_mode)
> > > > +		sai->slot_width = word_width;
> > > 
> > > Could you pls explain a bit what's this overriding for?
> > > Or it might be better to put into a comment.
> > >
> > In machine driver, we should use snd_soc_dai_set_tdm_slot to set slots
> > and slot width. In my opinion, slots in machine driver means the slot
> > number of all channels. But in sai driver, the slots means the slot number
> > of one channel. So snd_soc_calc_bclk use fs*sample_size*channels*tdm_slots
> > to caculate bclk.
> 
> Could you pls use the standard way as you described for slot number
> in machine driver instead of defining some other meanings? That one
> is really confusing, not to mention a code without any comment.
> 
> You can add some extra local variables with extinguished names and
> calculate the slot number and channels you want without changing
> the original sai->slots and channels in the hw_params(). As you said,
> you only need that new slot number and channels for snd_soc_calc_bclk
> call. So you may also put this code right before the call -- a normal
> routine doesn't need to recalculate the special slots and channels,
> right?
> 
> Nicolin

Actually i don't kown which meaning is the standard way. Because i found
in wm8993 and wm8904 codec driver, they also use slots/channels to set 
tdm_slots in set_tdm_slot function.


Best Regards,
Zidan
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