linux-kernel - Re: [PATCH 2/3] iio: imu: mpu6050: add level shifter flag

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Date:   Mon, 25 Sep 2023 15:28:15 +0300
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Andreas Kemnade <andreas@...nade.info>
Cc:     jic23@...nel.org, lars@...afoo.de, robh+dt@...nel.org,
        krzysztof.kozlowski+dt@...aro.org, conor+dt@...nel.org,
        bcousson@...libre.com, tony@...mide.com,
        jean-baptiste.maneyrol@....com, chenhuiz@...s.com,
        linux-iio@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-omap@...r.kernel.org
Subject: Re: [PATCH 2/3] iio: imu: mpu6050: add level shifter flag

On Mon, Sep 25, 2023 at 3:04 PM Andreas Kemnade <andreas@...nade.info> wrote:
> On Mon, 25 Sep 2023 14:07:58 +0300
> Andy Shevchenko <andy.shevchenko@...il.com> wrote:
> > On Mon, Sep 25, 2023 at 1:26 AM Andreas Kemnade <andreas@...nade.info> wrote:
> > >
> > > Some boards fail in magnetometer probe if flag is not set.
> >
> > Which flag? Can you elaborate a bit more?
> >
> well see $subj. The level shifter flag.

Well. it is better to have the commit message being self-contained.

> > Does it deserve the Fixes tag?
> >
> As there are only certain boards affected, they would also have
> to add the flag in dtb, I do not think it deservers a Fixes tag.
> Even in the board I have here, there are basically two
> mpu9150 connected per cable, only one of them needs the flag.

OK.

...

> > >         unsigned int val;
> > >         int ret;
> >
> > > +       ret = regmap_update_bits(st->map, 0x1, 0x80,
> > > +                                st->level_shifter ? 0x80 : 0);
> >
> > This is a bit cryptic, what does 1 stand for?
> >
> Well, I do not find anything in
> https://invensense.tdk.com/wp-content/uploads/2015/02/MPU-9150-Register-Map.pdf
> I have just found a similar line in the ancient 3.0 vendor kernel. No symbolic
> names there.

Okay, perhaps a comment on top to point out this ("the code based on
v3.0 vendor kernel, the meaning is unknown").

-- 
With Best Regards,
Andy Shevchenko