linux-kernel - Re: [PATCH 3/5] ASoC: dwc: Iterate over all channels

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Date:	Thu, 4 Dec 2014 12:25:30 +0530
From:	rajeev kumar <rajeevkumar.linux@...il.com>
To:	Mark Brown <broonie@...nel.org>
Cc:	Andrew Jackson <Andrew.Jackson@....com>,
	Jaroslav Kysela <perex@...ex.cz>, Takashi Iwai <tiwai@...e.de>,
	"alsa-devel@...a-project.org" <alsa-devel@...a-project.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Liam Girdwood <lgirdwood@...il.com>,
	Liviu Dudau <Liviu.Dudau@....com>
Subject: Re: [PATCH 3/5] ASoC: dwc: Iterate over all channels

On Wed, Dec 3, 2014 at 10:59 PM, Mark Brown <broonie@...nel.org> wrote:
> On Wed, Dec 03, 2014 at 04:39:01PM +0000, Andrew Jackson wrote:
>
>> +     /* Iterate over set of channels - independently controlled.
>> +      */
>> +     do {
>> +             if (substream->stream == SNDRV_PCM_STREAM_PLAYBACK) {
>> +                     i2s_write_reg(dev->i2s_base, TCR(ch_reg),
>> +                                   xfer_resolution);
>> +                     i2s_write_reg(dev->i2s_base, TFCR(ch_reg), 0x02);
>> +                     irq = i2s_read_reg(dev->i2s_base, IMR(ch_reg));
>> +                     i2s_write_reg(dev->i2s_base, IMR(ch_reg), irq & ~0x30);
>> +                     i2s_write_reg(dev->i2s_base, TER(ch_reg), 1);
>> +             } else {
>> +                     i2s_write_reg(dev->i2s_base, RCR(ch_reg),
>> +                                   xfer_resolution);
>> +                     i2s_write_reg(dev->i2s_base, RFCR(ch_reg), 0x07);
>> +                     irq = i2s_read_reg(dev->i2s_base, IMR(ch_reg));
>> +                     i2s_write_reg(dev->i2s_base, IMR(ch_reg), irq & ~0x03);
>> +                     i2s_write_reg(dev->i2s_base, RER(ch_reg), 1);
>> +             }
>> +     } while (ch_reg-- > 0);
>
> The normal way to write an iteration would be with a for loop - why are
> we not doing that?
>
> Also I see that you've not sent these as a single thread - please use
> --thread.

designware i2s has individual register for channel support. It is like
TCR(0), TCR(1) and so on.. So a macro is defined to capture these
please check below #define

#define TCR(x)      (0x40 * x + 0x034)

and the same is true for capture also. So there is no need for
iteration. Only writing to the particular register will do the work.

~Rajeev
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