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

Lars-Peter Clausen lars at metafoo.de
Thu Mar 27 10:19:54 CET 2014

On 03/26/2014 11:41 PM, Songhee Baek wrote:
>> -----Original Message-----
>> From: Lars-Peter Clausen [mailto:lars at metafoo.de]
>> Sent: Wednesday, March 26, 2014 12:39 PM
>> To: Arun Shamanna Lakshmi
>> Cc: lgirdwood at gmail.com; broonie at kernel.org; swarren at wwwdotorg.org;
>> Songhee Baek; alsa-devel at alsa-project.org; tiwai at suse.de; linux-
>> kernel at vger.kernel.org
>> Subject: Re: [alsa-devel] [PATCH] ASoC: Add support for multi register mux
>> On 03/26/2014 01:02 AM, Arun Shamanna Lakshmi wrote:
>>> If the mux uses 1 bit position per input, and requires to set one
>>> single bit at a time, then an N bit register can support up to N
>>> inputs. In more recent Tegra chips, we have at least greater than
>>> 64 inputs which requires at least 2 .reg fields in struct soc_enum.
>>> Signed-off-by: Arun Shamanna Lakshmi <aruns at nvidia.com>
>>> Signed-off-by: Songhee Baek <sbaek at nvidia.com>
>> 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?

>>> -	int reg;
>>> +	int reg[SOC_ENUM_MAX_REGS];
>>>    	unsigned char shift_l;
>>>    	unsigned char shift_r;
>>>    	unsigned int items;
>>> -	unsigned int mask;
>>> +	unsigned int mask[SOC_ENUM_MAX_REGS];
>> If you make mask and reg pointers instead of arrays this should be much
>> more flexible and not be limited to 3 registers.
> To use pointers instead of arrays, it will be flexible but I need to update SOC_ENUM SINGLE/DOUBLE macros.
> It will changes a lot in current soc-core.c and soc-dapm.c.

In the existing macros you can do something like this:
	.reg = &(unsigned int){(xreg)},

>>>    	const char * const *texts;
>>>    	const unsigned int *values;
>>> +	unsigned int num_regs;
>>>    };

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