linux-kernel - Re: [RFT][PATCH 2/2] regulator: lm363x: Fix n

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Message-ID: <CAFRkauBxJKcYbiT6UmKw81SAKm=AuDFu1Ez6Ttuc_EcMh_SudQ@mail.gmail.com>
Date:   Thu, 27 Jun 2019 07:58:23 +0800
From:   Axel Lin <axel.lin@...ics.com>
To:     Dan Murphy <dmurphy@...com>
Cc:     Mark Brown <broonie@...nel.org>,
        Liam Girdwood <lgirdwood@...il.com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFT][PATCH 2/2] regulator: lm363x: Fix n_voltages setting for lm36274

> > With your current code where LM36274_LDO_VSEL_MAX and n_voltages is 0x34,
> > the maximum voltage will become 400000 + 50000 * 0x34 = 6.6V which
> > does not match the datasheet.
>
> Not sure how you get 6.6v the LDO max is 6.5v.
>
> After 0x32->0x7f maps to 6.5v
>
> 000000 = 4 V
> 000001 = 4.05 V
> :
> 011110 = 5.5 V (Default)
> :
> 110010 = 6.5 V
>
> 110011 to 111111 map to 6.5 V <- Should never see 6.6v from LDO
>
> Page 7 of the Datasheet says range is 4v->6.5v
Hi Dan,

The device indeed can only support up to 6.5V, the point is you are using
linear equation to calculate the voltage of each selecter.
In your current code:
#define LM36274_LDO_VSEL_MAX           0x34 (and it's .n_voltages)
So it supports selector 0 ... 0x33.
For selector 0x33 in the linear equation is
4000000 + 50000 * 51 = 6550000 (i.e. 6.55V)
i.e. The device actually only support up to 6.5V but the driver
reports it support up to 6.55V
     because regulator_list_voltage() will return 6.55V for selector 0x33.
(I have off-by-one in my previous reply because when .n_voltages is
0x34, it supports up to 0x33)

Regards,
AXel