linux-kernel - Re: [PATCH] iio: adc: at91-sama5d2_adc: explain why indio_dev->name = dev

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Message-ID: <20250927165832.5ad37428@jic23-huawei>
Date: Sat, 27 Sep 2025 16:58:32 +0100
From: Jonathan Cameron <jic23@...nel.org>
To: Andy Shevchenko <andy.shevchenko@...il.com>
Cc: David Lechner <dlechner@...libre.com>, Nuno Sá
 <nuno.sa@...log.com>, Andy Shevchenko <andy@...nel.org>,
 linux-iio@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] iio: adc: at91-sama5d2_adc: explain why indio_dev->name
 = dev_name() is wrong

On Sun, 21 Sep 2025 21:33:02 +0300
Andy Shevchenko <andy.shevchenko@...il.com> wrote:

> On Sat, Sep 20, 2025 at 7:44 PM David Lechner <dlechner@...libre.com> wrote:
> >
> > Add an explanatory comment on why indio_dev->name = dev_name(dev) is
> > wrong, and that we can't fix it without breaking userspace.
> >
> > The idea is to prevent future drivers from making the same mistake by
> > copying this code. And if this driver is ever modified again, we can
> > at least make sure any new compatible IDs use the correct name.  
> 
> ...
> 
> > +       /*
> > +        * The device name is supposed to be the "part number", not the kobject
> > +        * name. Do not copy this code for new drivers. We can't "fix" this
> > +        * without breaking userspace, so we have to live with it. However, if
> > +        * any new compatible IDs are added, please do something similar to
> > +        * adc/ltc2497-core.c so that at least the new part numbers are correct.  
> 
> Please, use the full path from the root of the source tree, i.e.
> drivers/iio/adc/ltc2497-core.c. IIRC the Sphynx might even render the
> links properly (if it ever goes to this deep comment, which is not
> marked as kernel-doc).

Other than that this looks like a good approach to me.
I was thinking maybe a reference to central doc, but that might be a bit fragile
so I think I prefer this approach of stating it fully at each place it matters.

Thanks,

Jonathan

> 
> > +        */
> >         indio_dev->name = dev_name(&pdev->dev);  
>