linux-kernel - Re: [PATCH 3/4] iio: backend: make use of dev_errp

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Date: Mon, 08 Apr 2024 11:01:11 +0200
From: Nuno Sá <noname.nuno@...il.com>
To: Jonathan Cameron <jic23@...nel.org>, Andy Shevchenko
	 <andriy.shevchenko@...ux.intel.com>
Cc: Nuno Sa <nuno.sa@...log.com>, Petr Mladek <pmladek@...e.com>, Lars-Peter
 Clausen <lars@...afoo.de>, Olivier Moysan <olivier.moysan@...s.st.com>,
 Jyoti Bhayana <jbhayana@...gle.com>, Chris Down <chris@...isdown.name>,
 John Ogness <john.ogness@...utronix.de>, Greg Kroah-Hartman
 <gregkh@...uxfoundation.org>,  linux-kernel@...r.kernel.org,
 linux-iio@...r.kernel.org
Subject: Re: [PATCH 3/4] iio: backend: make use of dev_errp_probe()

On Sat, 2024-04-06 at 17:07 +0100, Jonathan Cameron wrote:
> On Thu, 4 Apr 2024 18:12:25 +0300
> Andy Shevchenko <andriy.shevchenko@...ux.intel.com> wrote:
> 
> > On Thu, Apr 04, 2024 at 04:58:27PM +0200, Nuno Sá wrote:
> > > On Thu, 2024-04-04 at 15:23 +0300, Andy Shevchenko wrote:  
> > > > On Thu, Apr 04, 2024 at 01:06:25PM +0200, Nuno Sa wrote:  
> > > > > Using dev_errp_probe() to simplify the code.  
> > 
> > ...
> > 
> > > > > +	if (IS_ERR(fwnode))
> > > > > +		return dev_errp_probe(dev, PTR_ERR(fwnode),
> > > > > +				      "Cannot get Firmware
> > > > > reference\n");  
> > > > 
> > > > ERR_CAST() seems quite good candidate to have here.
> > > > 
> > > > 		return dev_errp_probe(dev, fwnode, "Cannot get Firmware
> > > > reference\n");
> > > > 
> > > > (Assuming dev_errp_probe() magically understands that, note you may have
> > > > it as
> > > >  a macro and distinguish parameter type with _Generic() or so and behave
> > > >  differently: ERR_PTR() vs. ERR_CAST(), see acpi_dev_hid_uid_match()
> > > >  implementation, but also keep in mind that it doesn't distinguish
> > > > NULL/0,
> > > > there
> > > >  is a patch available in the mailing list to fix that, though.)  
> > > 
> > > Do we care that much for going with that trouble?  
> > 
> > I don't think we do. We are not supposed to be called with ret == 0/NULL.
> > That's why I pointed out to the current version.
> > 
> > > I understand like this we go
> > > PTR_ERR() to then comeback to ERR_PTR() but this for probe() which is not
> > > a
> > > fastpath. So perhaps we could just keep it simple?  
> > 
> > It's not about performance, it's about readability. See the difference
> > between
> > yours and mine.
> > 
> 
> You are suggesting making it transparently take an error ptr or an integer?
> Whilst clever, I'm not seeing that as a good idea for readability /
> reviewability.
> I expect something that looks like a function to take the same parameters
> (other vargs)
> always.  _Generic messes with that.

> Maybe I just don't like to learn new things!  If consensus comes down in
> favour
> of _Generic trickery then I'll get used to it eventually.
> 

Yeah, I agree with the above. Not fully convinced but for the ERR_CAST() case I
would very much prefer to have another explicit helper rather than hiding stuff
in the same macro.

- Nuno Sá