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

[Rajendra Nayak]

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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