linux-kernel - Re: [alsa-devel] [PATCH] ASoC: Add support for multi register mux

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Date:	Sat, 29 Mar 2014 11:53:13 +0100
From:	Lars-Peter Clausen <lars@...afoo.de>
To:	Songhee Baek <sbaek@...dia.com>
CC:	Arun Shamanna Lakshmi <aruns@...dia.com>,
	"'lgirdwood@...il.com'" <lgirdwood@...il.com>,
	"'broonie@...nel.org'" <broonie@...nel.org>,
	"'swarren@...dotorg.org'" <swarren@...dotorg.org>,
	"'alsa-devel@...a-project.org'" <alsa-devel@...a-project.org>,
	"'tiwai@...e.de'" <tiwai@...e.de>,
	"'linux-kernel@...r.kernel.org'" <linux-kernel@...r.kernel.org>
Subject: Re: [alsa-devel] [PATCH] ASoC: Add support for multi register mux

On 03/29/2014 03:30 AM, Songhee Baek wrote:
>> -----Original Message-----
>> From: Songhee Baek
>> Sent: Friday, March 28, 2014 11:10 AM
>> To: 'Lars-Peter Clausen'
>> Cc: Arun Shamanna Lakshmi; 'lgirdwood@...il.com'; 'broonie@...nel.org';
>> 'swarren@...dotorg.org'; 'alsa-devel@...a-project.org'; 'tiwai@...e.de';
>> 'linux-kernel@...r.kernel.org'
>> Subject: RE: [alsa-devel] [PATCH] ASoC: Add support for multi register mux
>>
>>
>>>> On 03/26/2014 11:41 PM, Songhee Baek wrote:
>>>>>> On 03/26/2014 01:02 AM, Arun Shamanna Lakshmi wrote:
>>>>>>
>>>>>> The way you describe this it seems to me that a value array for
>>>>>> this kind of mux would look like.
>>>>>>
>>>>>> 0x00000000, 0x00000000, 0x00000001 0x00000000, 0x00000000,
>>>>>> 0x00000002 0x00000000, 0x00000000, 0x00000003 0x00000000,
>>>>>> 0x00000000, 0x00000004 0x00000000, 0x00000000, 0x00000008 ...
>>>>>>
>>>>>> That seems to be extremely tedious. If the MUX uses a one hot
>>>>>> encoding how about storing the index of the bit in the values
>>>>>> array and use (1 << value) when writing the value to the register?
>>>>>
>>>>> If we store the index of the bit, the value will be duplicated for
>>>>> each
>>>> registers inputs since register has 0 to 31bits to shift, then we
>>>> need to decode the index to interpret value for which registers to
>>>> set. If we need to interpret the decoded value of index, it is
>>>> better to have custom put/get function in our driver, isn't it?
>>>>>
>>>>
>>>> I'm not sure I understand. If you use (val / 32) to pick the
>>>> register and (val %
>>>> 32) to pick the bit in the register this should work just fine.
>>>> Maybe I'm missing something. Do you have a real world code example
>>>> of of the this type of enum is used?
>>>>
>>>
>>> I can use val/32 and val%32 for this multi register mux.
>>
> With this logic, put function would be easy however get function becomes tedious due to looping on each bit per register for 3 of them in our case. Rather, it would be easy to identify a unique MUX_OFFSET to distinguish between the 3
> registers as shown in the code below.

I'm not sure I understand how that MUX_OFFSET would work. To get the 
selected mux output you can use the ffs instruction.

foreach(reg) {
	reg_val = read(reg) & mask;
	if (reg_val != 0) {
		val = __ffs(reg_val);
		break;
	}
}

- Lars
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