linux-kernel - Re: [PATCH v2 1/1] iio: adc: qcom-spmi-adc5: Fix the channel name

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Date:   Wed, 25 Jan 2023 19:39:46 +0000
From:   Matthias Kaehlcke <mka@...omium.org>
To:     Doug Anderson <dianders@...omium.org>
Cc:     Konrad Dybcio <konrad.dybcio@...aro.org>,
        Jonathan Cameron <jic23@...nel.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Jonathan Cameron <Jonathan.Cameron@...wei.com>,
        Nuno Sá <nuno.sa@...log.com>,
        linux-arm-msm@...r.kernel.org, linux-iio@...r.kernel.org,
        linux-kernel@...r.kernel.org, Andy Gross <agross@...nel.org>,
        Bjorn Andersson <andersson@...nel.org>,
        Lars-Peter Clausen <lars@...afoo.de>,
        Marijn Suijten <marijn.suijten@...ainline.org>,
        Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
Subject: Re: [PATCH v2 1/1] iio: adc: qcom-spmi-adc5: Fix the channel name

On Mon, Jan 23, 2023 at 03:12:06PM -0800, Doug Anderson wrote:
> Hi,
> 
> On Mon, Jan 23, 2023 at 8:35 AM Konrad Dybcio <konrad.dybcio@...aro.org> wrote:
> >
> > On 22.01.2023 18:24, Jonathan Cameron wrote:
> > > On Wed, 18 Jan 2023 12:06:23 +0200
> > > Andy Shevchenko <andriy.shevchenko@...ux.intel.com> wrote:
> > >
> > >> The node name can contain an address part which is unused
> > >> by the driver. Moreover, this string is propagated into
> > >> the userspace label, sysfs filenames *and breaking ABI*.
> > >>
> > >> Cut the address part out before assigning the channel name.
> > >>
> > >> Fixes: 4f47a236a23d ("iio: adc: qcom-spmi-adc5: convert to device properties")
> > >> Reported-by: Marijn Suijten <marijn.suijten@...ainline.org>
> > >> Signed-off-by: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
> > >
> > > LGTM, but given it will have ABI impact, I'd like to hear from
> > > Andy, Bjorn or Konrad as maintainers and /or Dmitry as someone
> > > who has touched this driver fairly recently.
> > + Doug
> >
> > Unless the Chromium folks relied on the old names (they're the
> > only ones I can think of that actually could have tapped into
> > this), I say green light!
> 
> Thanks for the CC. I _think_ the only place we use these ADCs is for
> certain thermistors and I think that those are all just hooked up in
> the device tree, so the channel name doesn't matter. I'll also note
> that no Qualcomm Chromebooks are shipping with anything newer than
> kernel 5.15 right now, and (I checked) the ChromeOS 5.15 tree doesn't
> have commit 4f47a236a23d ("iio: adc: qcom-spmi-adc5: convert to device
> properties"). Thus, even if I'm wrong and the name is used someplace
> hidden then the "old" name would be better for us. I haven't tested
> the patch myself, but it sounds as if ${SUBJECT} patch is actually
> moving us back to the old name.
> 
> +Matthias to keep me honest since he's spent more time with the ADCs.

Agreed that the channel name doesn't matter, Chrome OS currently only
uses the ADCs for thermal zones controlled by the kernel.

> > > Mostly I want to be sure they know this exists before it causes surprise.
> > >
> > > Jonathan
> > >
> > >> ---
> > >> v2: rephrased commit message (Marijn), fixed compilation issue (Marijin)
> > >>  drivers/iio/adc/qcom-spmi-adc5.c | 10 +++++++++-
> > >>  1 file changed, 9 insertions(+), 1 deletion(-)
> > >>
> > >> diff --git a/drivers/iio/adc/qcom-spmi-adc5.c b/drivers/iio/adc/qcom-spmi-adc5.c
> > >> index e90c299c913a..c2d5e06f137a 100644
> > >> --- a/drivers/iio/adc/qcom-spmi-adc5.c
> > >> +++ b/drivers/iio/adc/qcom-spmi-adc5.c
> > >> @@ -628,12 +628,20 @@ static int adc5_get_fw_channel_data(struct adc5_chip *adc,
> > >>                                  struct fwnode_handle *fwnode,
> > >>                                  const struct adc5_data *data)
> > >>  {
> > >> -    const char *name = fwnode_get_name(fwnode), *channel_name;
> > >> +    const char *channel_name;
> > >> +    char *name;
> > >>      u32 chan, value, varr[2];
> > >>      u32 sid = 0;
> > >>      int ret;
> > >>      struct device *dev = adc->dev;
> > >>
> > >> +    name = devm_kasprintf(dev, GFP_KERNEL, "%pfwP", fwnode);
> > >> +    if (!name)
> > >> +            return -ENOMEM;
> > >> +
> > >> +    /* Cut the address part */
> > >> +    name[strchrnul(name, '@') - name] = '\0';
> > >> +
> > >>      ret = fwnode_property_read_u32(fwnode, "reg", &chan);
> > >>      if (ret) {
> > >>              dev_err(dev, "invalid channel number %s\n", name);
> > >