linux-kernel - Re: [bug report] iio: dac: adding support for Microchip MCP47FEB02

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Message-ID: <CAHp75VdhTEKu2tKC+UKJLs1DcE7079KEbPV0NTFfUAjADBEg_g@mail.gmail.com>
Date: Fri, 6 Feb 2026 17:57:14 +0200
From: Andy Shevchenko <andy.shevchenko@...il.com>
To: Dan Carpenter <dan.carpenter@...aro.org>
Cc: Andy Shevchenko <andriy.shevchenko@...el.com>, Ariana Lazar <ariana.lazar@...rochip.com>, 
	David Lechner <dlechner@...libre.com>, Nuno Sá <nuno.sa@...log.com>, 
	Andy Shevchenko <andy@...nel.org>, linux-iio@...r.kernel.org, 
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [bug report] iio: dac: adding support for Microchip MCP47FEB02

On Fri, Feb 6, 2026 at 5:32 PM Dan Carpenter <dan.carpenter@...aro.org> wrote:
> On Fri, Feb 06, 2026 at 05:14:53PM +0200, Andy Shevchenko wrote:
> > On Fri, Feb 06, 2026 at 05:33:26PM +0300, Dan Carpenter wrote:
> > > On Fri, Feb 06, 2026 at 04:04:07PM +0200, Andy Shevchenko wrote:
> > > > > drivers/iio/dac/mcp47feb02.c
> > > > >     712 static int mcp47feb02_init_scales_avail(struct mcp47feb02_data *data, int vdd_mV,
> > > > >     713                                         int vref_mV, int vref1_mV)
> > > > >     714 {
> > > > >     715         struct device *dev = regmap_get_device(data->regmap);
> > > > >     716         int tmp_vref;
> > > > >     717
> > > > >     718         mcp47feb02_init_scale(data, MCP47FEB02_SCALE_VDD, vdd_mV, data->scale);
> > > > >     719
> > > > >     720         if (data->use_vref)
> > > > >     721                 tmp_vref = vref_mV;
> > > > >     722         else
> > > > >     723                 tmp_vref = MCP47FEB02_INTERNAL_BAND_GAP_mV;
> > > > >     724
> > > > >     725         mcp47feb02_init_scale(data, MCP47FEB02_SCALE_GAIN_X1, tmp_vref, data->scale);
> > > > >     726         mcp47feb02_init_scale(data, MCP47FEB02_SCALE_GAIN_X2, tmp_vref * 2, data->scale);
> > > > >     727
> > > > >     728         if (data->phys_channels >= 4) {
> > > > >     729                 mcp47feb02_init_scale(data, MCP47FEB02_SCALE_VDD, vdd_mV, data->scale_1);
> > > > >     730
> > > > >     731                 if (data->use_vref1 && vref1_mV <= 0)
> > > > > --> 732                         return dev_err_probe(dev, vref1_mV, "Invalid voltage for Vref1\n");
> > > > >                                                           ^^^^^^^^
> > > > > vref1_mV is not a valid error code.
> > > >
> > > > Why not? When it's negative I believe the above statement is not true.
> > >
> > > I saw this as just sanity checking the input.  vref1_mV is never
> > > actually negative.  I don't know if devm_regulator_get_enable_read_voltage()
> > > can return less than one millivolt.
> >
> >  * In cases where the supply is not strictly required, callers can check for
> >  * -ENODEV error and handle it accordingly.
> >  *
> >  * Returns: voltage in microvolts on success, or an negative error number on failure.
> >
> > What did I miss?
> >
>
> drivers/iio/dac/mcp47feb02.c
>   1157          if (chip_features->have_ext_vref1) {
>   1158                  ret = devm_regulator_get_enable_read_voltage(dev, "vref1");
>   1159                  if (ret > 0) {
>   1160                          vref1_mV = ret / MILLI;
>
> Potentially, if ret is in the 1-999 range then vref1_mV could be zero,
> but it can't be negative.

I see, thanks!

So, it means that the validation should be moved here on ret < 0 and
ret < 1000 (if positive).

>   1161                          data->use_vref1 = true;
>   1162                  } else {
>   1163                          dev_dbg(dev, "using internal band gap as voltage reference 1.\n");
>   1164                          dev_dbg(dev, "Vref1 is unavailable.\n");

But... ret < 0  is checked here.
Hence the only one left is the range [0..999].

>   1165                  }
>   1166          }
>   1167
>   1168          ret = mcp47feb02_init_ctrl_regs(data);
>   1169          if (ret)
>   1170                  return dev_err_probe(dev, ret, "Error initialising vref register\n");
>   1171
>   1172          ret = mcp47feb02_init_ch_scales(data, vdd_mV, vref_mV, vref1_mV);
>                                                                        ^^^^^^^^
>
>   1173          if (ret)
>   1174                  return ret;


-- 
With Best Regards,
Andy Shevchenko