linux-kernel - Re: [PATCH v3] Add ltc3562 voltage regulator driver

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Message-ID: <545A0CEE.2050101@topic.nl>
Date:	Wed, 5 Nov 2014 12:41:34 +0100
From:	Mike Looijmans <mike.looijmans@...ic.nl>
To:	Mark Brown <broonie@...nel.org>
CC:	<lgirdwood@...il.com>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3] Add ltc3562 voltage regulator driver

On 11/04/2014 09:26 PM, Mark Brown wrote:
> On Tue, Nov 04, 2014 at 07:50:45AM +0100, Mike Looijmans wrote:
>
>> v3: Add .of_match_table and prefix lltc
>>      Clarify why regmap cannot be used
>>      Add lltc,operating-mode (0..3) DT property
>>      regulator child nodes are optional
>
> Leave out the mode setting in the DT for now please, Javier was looking
> at adding a standard property for this with a driver defined mapping to
> modes - you should implement the standard get_mode() and set_mode() (but
> can always do that as a followup).
>
>> +/* the LTC3562 does not have a register map, instead it receives a two-byte
>> + * command set. The first byte sets the mask for the output(s) to be programmed
>> + * and the second byte hold the "enable" bit and the DAC code. */
>> +struct ltc3562_status {
>> +	u8 addr_mode;	/* sub-address byte: program mask an operating mode */
>> +	u8 enable_daccode;	/* data byte: Enable bit and DAC code  */
>> +};
>
> So, I managed to find a datasheet[1] and this does actually seem to be a
> standard register map.  It looks like this is a 4x12 register map with
> the program bytes being essentially register addresses (called sub
> addresses in the datasheet), two pad bits (normally we'd include these
> in the data for convenience) and the rest of the bits data.  What am I
> missing here?
>
> Otherwise this looks good.
>
> [1] http://cds.linear.com/docs/en/datasheet/3562fa.pdf
>

Things that makes me think it's NOT a register map:
- You cannot read from the device
- You always have to send a complete command set (two bytes)
- There is data (the regulator mode) in the address byte
- The 'address' is not an index but a bitmask in bits 4..7

Yeah, I think you can force-feed this to regmap. It will just make the code 
considerably bigger and harder to understand, and as far as I know, the one 
and only advantage this will bring is that you can dump the current 
"registers" (4x10 bits of data) via /sys/kernel/debug/regmap.

I fail to see the use for regmap here, but if your view on this is "regmap or 
burst" then I'll implement it.

Mike.


Met vriendelijke groet / kind regards,

Mike Looijmans
System Expert


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