# Re: [PATCH RFT 1/2] regulator: twl: Fix the formula to calculatevsel and voltage for twl6030ldo

From: Rajendra Nayak
Date: Mon Jul 16 2012 - 05:11:14 EST

Hi Axel,

My apologies for the delay in responding to this one.

On Monday 09 July 2012 04:31 PM, Axel Lin wrote:
æ äï2012-07-09 æ 11:22 +0800ïAxel Lin æåï
In twl6030ldo_set_voltage, current code use below formula to calculate vsel:
vsel = (min_uV/1000 - 1000)/100 + 1;
This is worng because when min_uV is 1000000 uV, vsel is 1.
It should be 0 in this case.

Why? Do you know of any documentation which states this?
I am referring to the twl6030 Top Functional spec version 1.18
and Table - 223 "LDO Output Voltage Selection Code" clearly
states that the vsel should be 1 when voltage expected is 1000000 uV.

Also refer to equation 3 "LDO Output Voltage Selection Code" in the
same document and you will see this mentioned..
Absolute Voltage value = 1.0V + 0.1V * (binary value â 00000001)

Fix it by change the equation to: (This equation is common for linear mapping)
vsel = DIV_ROUND_UP(min_uV - rdev->desc->min_uV, rdev->desc->uV_step);

In twl6030ldo_get_voltage, current code use below formula to calculate voltage:
mV = 1000mv + 100mv * (vsel - 1)
This is worng because when vsel is 0, mV is 900mV. Note the min_uV is 1000mV.
Fix it by change the equation to: (This equation is common for linear mapping)
return rdev->desc->min_uV + vsel * rdev->desc->uV_step;

While I'm thinking I need to rework this patch so that it doesn't use
rdev->desc->min_uV and rdev->desc->uV_step and then can be applied
to current Linus' tree.

But while I am tracking back to commit 3e3d3be79c
Author: Rajendra Nayak<rnayak@xxxxxx>
Date: Thu Apr 22 14:18:32 2010 +0530

twl6030: regulator: Remove vsel tables and use formula for
calculation

All twl6030 regulators can be programmed from 1.0v to 3.3v
with 100mV steps.
The below formula can be used to calculate the vsel values
to be programmed in the VREG_VOLTAGE registers.

Voltage(in mV) = 1000mv + 100mv * (vsel - 1)

Ex: if vsel = 0x9, mV = 1000 + 100 * (9 -1) = 1800mV.

This patch removes all existing VSEL tables for twl6030 adjustable
regulators and just uses the formula directly for vsel calculations
after verifing they fall in the allowed range.

Signed-off-by: Rajendra Nayak<rnayak@xxxxxx>

I found a problem that before commit 3e3d3be79c, the voltage tables were
not linear mapping. So why we can convert these voltage mapping table to
Voltage(in mV) = 1000mv + 100mv * (vsel - 1)?

Did I miss something?

All voltage tables before commit '3e3d3be79c' for twl6030 regulators
were clearly wrong. They assumed similarity with twl4030 regulators
which was not right.

regards,
Rajendra

Regards,
Axel

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