Re: [PATCH v1] iio: adc: MCP3564: fix warn: unsigned '__x' is never less than zero.

[Marius.Cristea]

  Hi Jonathan,

 Sorry, I think I've made a "mistake" related to naming the patches and
also not running the Smatch checker at a point in time.



On Tue, 2023-10-10 at 10:44 +0100, Jonathan Cameron wrote:
> EXTERNAL EMAIL: Do not click links or open attachments unless you
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> 
> On Mon, 2 Oct 2023 19:16:18 +0300
> <marius.cristea@xxxxxxxxxxxxx> wrote:
> 
> > From: Marius Cristea <marius.cristea@xxxxxxxxxxxxx>
> > 
> > The patch efea15e3c65d: "iio: adc: MCP3564: fix the static checker
> > warning"
> > leads to the following Smatch static checker warning:
> > 
> >    smatch warnings:
> >    drivers/iio/adc/mcp3564.c:1105 mcp3564_fill_scale_tbls() warn:
> > unsigned '__x' is never less than zero.
> > 
> > vim +/__x +1105 drivers/iio/adc/mcp3564.c
> > 
> >    1094
> >    1095  static void mcp3564_fill_scale_tbls(struct mcp3564_state
> > *adc)
> >    1096  {
> >    .....
> >    1103          for (i = 0; i < MCP3564_MAX_PGA; i++) {
> >    1104                  ref = adc->vref_mv;
> >  > 1105                  tmp1 = shift_right((u64)ref * NANO, pow);
> >    1106                  div_u64_rem(tmp1, NANO, &tmp0);
> >    1107
> >    .....
> >    1113  }
> > 
> > Reported-by: kernel test robot <lkp@xxxxxxxxx>
> > Closes:
> > https://lore.kernel.org/oe-kbuild-all/202309280738.NWjVfVt4-lkp@xxxxxxxxx/
> > Fixes: efea15e3c65d (iio: adc: MCP3564: fix the static checker
> > warning)
> 
> This fix is fine but can you talk me through how the static checker
> warning fix
> in question has anything to do with this one?
> 
> Was it just a case of fixing that issue allowing the static checker
> to
> get further before giving up?  In which case the description needs
> modifying.
> 
> Or am I missing something in the following fix?
> 
> diff --git a/drivers/iio/adc/mcp3564.c b/drivers/iio/adc/mcp3564.c
> index 64145f4ae55c..9ede1a5d5d7b 100644
> --- a/drivers/iio/adc/mcp3564.c
> +++ b/drivers/iio/adc/mcp3564.c
> @@ -1422,11 +1422,8 @@ static int mcp3564_probe(struct spi_device
> *spi)
>         struct mcp3564_state *adc;
> 
>         indio_dev = devm_iio_device_alloc(&spi->dev, sizeof(*adc));
> -       if (!indio_dev) {
> -               dev_err_probe(&indio_dev->dev, PTR_ERR(indio_dev),
> -                             "Can't allocate iio device\n");
> +       if (!indio_dev)
>                 return -ENOMEM;
> -       }
> 
> 

  I've got two bugs reported:

- The first one was reported by Dan Carpenter "Re: [bug report] iio:
adc: adding support for MCP3564 ADC". This bug was found using the
"Smatch static checker warning" and it was related to:
> --> 1426                 dev_err_probe(&indio_dev->dev,
PTR_ERR(indio_dev),

This bug was fixed by the above "[PATCH v1] iio: adc: MCP3564: fix the
static checker warning" and it was applied on "Applied to the togreg
branch of iio.git as that's where this driver is at the moment."

Also my mistake at this point was that I didn't setup and run the
"Smatch static checker warning"


> as that's all I'm seeing in that commit.
> 
Yes, that commit only handled part of the fix.



> > Signed-off-by: Marius Cristea <marius.cristea@xxxxxxxxxxxxx>
> > ---
> >  drivers/iio/adc/mcp3564.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/drivers/iio/adc/mcp3564.c b/drivers/iio/adc/mcp3564.c
> > index 9ede1a5d5d7b..e3f1de5fcc5a 100644
> > --- a/drivers/iio/adc/mcp3564.c
> > +++ b/drivers/iio/adc/mcp3564.c
> > @@ -1102,7 +1102,7 @@ static void mcp3564_fill_scale_tbls(struct
> > mcp3564_state *adc)
> > 
> >       for (i = 0; i < MCP3564_MAX_PGA; i++) {
> >               ref = adc->vref_mv;
> > -             tmp1 = shift_right((u64)ref * NANO, pow);
> > +             tmp1 = ((u64)ref * NANO) >> pow;
> >               div_u64_rem(tmp1, NANO, &tmp0);
> > 
> >               tmp1 = tmp1 * mcp3564_hwgain_frac[(2 * i) + 1];
> > 
> > base-commit: 5e99f692d4e32e3250ab18d511894ca797407aec
> 

- The second bug was reported by "kernel test robot <lkp@xxxxxxxxx>"
also by running Smatch and it was run on the initial driver (without
having the first patch applied)

smatch warnings:
drivers/iio/adc/mcp3564.c:1105 mcp3564_fill_scale_tbls() warn: unsigned
'__x' is never less than zero.
drivers/iio/adc/mcp3564.c:1426 mcp3564_probe() warn: passing zero to
'PTR_ERR'
drivers/iio/adc/mcp3564.c:1426 mcp3564_probe() warn: address of NULL
pointer 'indio_dev'


The:"drivers/iio/adc/mcp3564.c:1426 mcp3564_probe() warn: passing zero
to 'PTR_ERR'" and "drivers/iio/adc/mcp3564.c:1426 mcp3564_probe() warn:
address of NULL pointer 'indio_dev'" were fixed by the first patch.

The "drivers/iio/adc/mcp3564.c:1105 mcp3564_fill_scale_tbls() warn:
unsigned '__x' is never less than zero." is fixed by the last patch
"[PATCH v1] iio: adc: MCP3564: fix warn: unsigned '__x' is never less
than zero."
 by changeing:

-		tmp1 = shift_right((u64)ref * NANO, pow);
+		tmp1 = ((u64)ref * NANO) >> pow;

shift_right function is "Required to safely shift negative values" but
my value is always unsigned so it doesn't make sense to used it. This
error was reported when I have run the Smatch over the driver + first
patch (what was the latest from togreg).

I have applied the patch on top of what was the "latest" from togreg
branch and not on the initial driver.


I could change the description or I could provide a patch to handle
both warning reporting at once.

Thanks,
Marius