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

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Message-ID: <Y8fyonSp49QoAb8v@smile.fi.intel.com>
Date:   Wed, 18 Jan 2023 15:22:42 +0200
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     Marijn Suijten <marijn.suijten@...ainline.org>
Cc:     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>,
        Konrad Dybcio <konrad.dybcio@...aro.org>,
        Jonathan Cameron <jic23@...nel.org>,
        Lars-Peter Clausen <lars@...afoo.de>
Subject: Re: [PATCH v2 1/1] iio: adc: qcom-spmi-adc5: Fix the channel name

On Wed, Jan 18, 2023 at 01:35:28PM +0100, Marijn Suijten wrote:
> On 2023-01-18 12:06:23, Andy Shevchenko 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>
> 
> Reviewed-by: Marijn Suijten <marijn.suijten@...ainline.org>

Thank you!

My answers below.

...

> > +	name = devm_kasprintf(dev, GFP_KERNEL, "%pfwP", fwnode);
> 
> Is this better/cleaner than copying the string from fwnode_get_name?

Coying to where? And what would be the lifetime of that string?

With devm_kasprintf():
- we don't care how long the string is
- we don't care about corner cases of lifetime as it's the same as
  device itself (i.o.w. the same as the IIO device container)

...

> > +	name[strchrnul(name, '@') - name] = '\0';
> 
> This is the same as *strchrnul(name, '@') = '\0'; if I'm not mistaken.

Yes, But it's harder to read and understand. I believe the compiler has
enough power to optimize this to the same assembly code.

-- 
With Best Regards,
Andy Shevchenko