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

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Date: Sat, 6 Apr 2024 20:54:17 +0200
From: Andi Shyti <andi.shyti@...nel.org>
To: Jonathan Cameron <jic23@...nel.org>
Cc: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>, 
	Nuno Sá <noname.nuno@...il.com>, 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()

Hi,

On Sat, Apr 06, 2024 at 05:07:17PM +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.

the whole point of the dev_err_...() functions is to add trickery
in order to reduce code and brackets.

The way I see this is to have a combination of functions:

 - takes integer, returns integer -> dev_err_probe()
 - takes integer, returns pointer -> dev_errp_probe() (or dev_err_ptr_probe())
 - takes pointer, return integer -> ? dev_ptr_err_probe()
 - takes pointer, returns pointer -> ? dev_ptr_probe()

Thoughts?

Andi