linux-kernel - Re: [PATCH v3 12/19] hwmon: (mr75203) fix voltage equation for negative source input

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Message-ID: <YxERTTubyKb9oy8P@smile.fi.intel.com>
Date:   Thu, 1 Sep 2022 23:08:45 +0300
From:   Andy Shevchenko <andriy.shevchenko@...el.com>
To:     "Farber, Eliav" <farbere@...zon.com>
Cc:     jdelvare@...e.com, linux@...ck-us.net, robh+dt@...nel.org,
        p.zabel@...gutronix.de, rtanwar@...linear.com,
        linux-hwmon@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, talel@...zon.com, hhhawa@...zon.com,
        jonnyc@...zon.com, hanochu@...zon.com, ronenk@...zon.com,
        itamark@...zon.com, shellykz@...zon.com, shorer@...zon.com,
        amitlavi@...zon.com, almogbs@...zon.com, dkl@...zon.com
Subject: Re: [PATCH v3 12/19] hwmon: (mr75203) fix voltage equation for
 negative source input

On Thu, Sep 01, 2022 at 03:47:39PM +0300, Farber, Eliav wrote:
> On 8/31/2022 3:04 PM, Andy Shevchenko wrote:
> > On Tue, Aug 30, 2022 at 07:22:05PM +0000, Eliav Farber wrote:
> > > According to Moortec Embedded Voltage Monitor (MEVM) series 3 data
> > > sheet,
> > > the minimum input signal is -100mv and maximum input signal is +1000mv.
> > > When n was small enough, such that PVT_N_CONST * n < PVT_R_CONST it
> > > resulted in n overflowing to a very large number (since n is u32 type).
> > > 
> > > This change fixes the problem by casting n to long and replacing shift
> > > right with div operation.
> > 
> > Fixes tag?
> 
> For v4 I modified the commit message to (hopefully) be more
> understandable:
> 
> "
> According to Moortec Embedded Voltage Monitor (MEVM) series 3 data
> sheet, the minimum input signal is -100mv and maximum input signal
> is +1000mv.
> 
> On 64 bit machines sizeof(u32) = 4 and sizeof(long) = 8.
> So when measuring a negative input and n is small enough, such that
> PVT_N_CONST * n < PVT_R_CONST, it results in n overflowing to a very
> large number which is not negative (because 4 MSB bytes of val are 0).
> 
> This change fixes the sign problem and supports negative values by
> casting n to long and replacing shift right with div operation.
> "

What I meant is to add the tag of the commit which this one is fixing.
We have Fixes tag format for that. You may see how it's done by looking
into Git history: git log --grep Fixes:

-- 
With Best Regards,
Andy Shevchenko