linux-kernel - Re: [PATCH 04/12] iio: adc: max9611: Fix misuse of GENMASK macro

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Date:   Wed, 31 Jul 2019 09:37:04 +0100
From:   Jonathan Cameron <jonathan.cameron@...wei.com>
To:     Jacopo Mondi <jacopo@...ndi.org>
CC:     Joe Perches <joe@...ches.com>, Jonathan Cameron <jic23@...nel.org>,
        "Jacopo Mondi" <jacopo+renesas@...ndi.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        <linux-kernel@...r.kernel.org>, Hartmut Knaack <knaack.h@....de>,
        "Lars-Peter Clausen" <lars@...afoo.de>,
        Peter Meerwald-Stadler <pmeerw@...erw.net>,
        <linux-iio@...r.kernel.org>
Subject: Re: [PATCH 04/12] iio: adc: max9611: Fix misuse of GENMASK macro

On Mon, 29 Jul 2019 23:52:14 +0200
Jacopo Mondi <jacopo@...ndi.org> wrote:

> Hello,
>   so I finally run some test and...
> 
> On Sun, Jul 14, 2019 at 05:19:32AM -0700, Joe Perches wrote:
> > On Sun, 2019-07-14 at 12:54 +0100, Jonathan Cameron wrote:  
> > > On Tue,  9 Jul 2019 22:04:17 -0700
> > > Joe Perches <joe@...ches.com> wrote:
> > >  
> > > > Arguments are supposed to be ordered high then low.
> > > >
> > > > Signed-off-by: Joe Perches <joe@...ches.com>  
> > >
> > > Applied to the fixes-togreg branch of iio.git and marked for
> > > stable etc.  
> 
> I don't see it in v5.3-rc2, has it been collected or are we still in
> time for an additional fix?
> 
> >
> > This mask is used in an init function called from a probe.
> >
> > I don't have this hardware but it looks as if it could
> > never have worked so I doubt the driver and the hardware
> > have ever been tested.
> >
> > Does anyone have this device in actual use?  
> 
> Because it turns out this is 2 times embarrassing. The mask definition
> is indeed wrong, as Joe reported and fixed, but also this line
> >
> > 	regval = ret & MAX9611_TEMP_MASK;  
> 
> is very wrong as regval is read as:
>         ret = max9611_read_single(max9611, CONF_TEMP, &regval);
> 
> So that should actually be:
>         regval &= MAX9611_TEMP_MASK;
> not
>  	regval = ret & MAX9611_TEMP_MASK;
> Ups...
> 
> Yes, it worked by chance, as regval was always 0, which is in the
> range of acceptable temperatures :/
> 
> >
> > 	if ((regval > MAX9611_TEMP_MAX_POS &&
> > 	     regval < MAX9611_TEMP_MIN_NEG) ||
> > 	     regval > MAX9611_TEMP_MAX_NEG) {  
> 
> Also reading this condition and how I had defined the temperature
> calculation formula makes me wonder if this it totally correct, but
> for the moment:
> 
> 1) if Joe's patch has been collected, I can send an additional patch to
> fix how regval is computed.
> 2) If Joe's patch still have to be collected, the regval computation
> might be fixed there.

I think this will have hit linux-next on the same day as your email.

https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/commit/drivers/iio/adc?id=ae8cc91a7d85e018c0c267f580820b2bb558cd48

So follow up patch please.

Thanks!

Jonathan
> 
> Sorry for taking so long to get back to you and thanks for noticing.
> 
> Thanks
>   j
> 
> > 		dev_err(max9611->dev,
> > 			"Invalid value received from ADC 0x%4x: aborting\n",
> > 			regval);
> > 		return -EIO;
> > 	}
> >
> >  
> > > Thanks,
> > >
> > > Jonathan
> > >  
> > > > ---
> > > >  drivers/iio/adc/max9611.c | 2 +-
> > > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > > >
> > > > diff --git a/drivers/iio/adc/max9611.c b/drivers/iio/adc/max9611.c
> > > > index 917223d5ff5b..0e3c6529fc4c 100644
> > > > --- a/drivers/iio/adc/max9611.c
> > > > +++ b/drivers/iio/adc/max9611.c
> > > > @@ -83,7 +83,7 @@
> > > >  #define MAX9611_TEMP_MAX_POS		0x7f80
> > > >  #define MAX9611_TEMP_MAX_NEG		0xff80
> > > >  #define MAX9611_TEMP_MIN_NEG		0xd980
> > > > -#define MAX9611_TEMP_MASK		GENMASK(7, 15)
> > > > +#define MAX9611_TEMP_MASK		GENMASK(15, 7)
> > > >  #define MAX9611_TEMP_SHIFT		0x07
> > > >  #define MAX9611_TEMP_RAW(_r)		((_r) >> MAX9611_TEMP_SHIFT)
> > > >  #define MAX9611_TEMP_SCALE_NUM		1000000  
> >  
>