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

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Date:	Thu, 04 Dec 2014 09:13:01 +0000
From:	Andrew Jackson <Andrew.Jackson@....com>
To:	rajeev kumar <rajeevkumar.linux@...il.com>,
	Mark Brown <broonie@...nel.org>
CC:	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 12/04/14 06:55, rajeev kumar wrote:
> 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.

However params_channels returns the number of channels that the device needs to configure.  So, for example, when there are four channels two sets of channel registers need to be programmed.


	Andrew
> 
> ~Rajeev
> 

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