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

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Message-ID: <5264b2cddd5d3cbba5e9d5e55f8c7069347ec38b.camel@gmail.com>
Date: Mon, 08 Apr 2024 11:05:39 +0200
From: Nuno Sá <noname.nuno@...il.com>
To: Andi Shyti <andi.shyti@...nel.org>, Jonathan Cameron <jic23@...nel.org>
Cc: Andy Shevchenko <andriy.shevchenko@...ux.intel.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()

On Sat, 2024-04-06 at 20:54 +0200, Andi Shyti wrote:
> 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.
> 

I'm not sure I'm completely convinced on having more helpers but also no strong
opinion tbh. But see below...

> 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()

This is pretty much all the dev_err_probe(dev, PTR_ERR(), ...) we already have
out there. Do we really want to have this variant?

>  - takes pointer, returns pointer -> ? dev_ptr_probe()

dev_ptr_probe() misses to be clear about being an error and think this is pretty
much the ERR_CAST() case right? Maybe dev_err_cast_ptr_probe()? Or
dev_err_cast_probe()?

- Nuno Sá