Message-ID: <20220120075718.5qtrpc543kkykaow@pengutronix.de>
Date:   Thu, 20 Jan 2022 08:57:18 +0100
From:   Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
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Subject: Re: [PATCH] driver core: platform: Rename
 platform_get_irq_optional() to platform_get_irq_silent()

On Wed, Jan 19, 2022 at 08:51:29PM +0200, Andy Shevchenko wrote:
> On Sat, Jan 15, 2022 at 04:45:39PM +0100, Uwe Kleine-König wrote:
> > On Fri, Jan 14, 2022 at 03:04:38PM +0200, Andy Shevchenko wrote:
> > > On Thu, Jan 13, 2022 at 08:43:58PM +0100, Uwe Kleine-König wrote:
> > > > > It'd certainly be good to name anything that doesn't correspond to one
> > > > > of the existing semantics for the API (!) something different rather
> > > > > than adding yet another potentially overloaded meaning.
> > > > 
> > > > It seems we're (at least) three who agree about this. Here is a patch
> > > > fixing the name.
> > > 
> > > And similar number of people are on the other side.
> > 
> > If someone already opposed to the renaming (and not only the name) I
> > must have missed that.
> > 
> > So you think it's a good idea to keep the name
> > platform_get_irq_optional() despite the "not found" value returned by it
> > isn't usable as if it were a normal irq number?
> 
> I meant that on the other side people who are in favour of Sergey's patch.
> Since that I commented already that I opposed the renaming being a standalone
> change.
> 
> Do you agree that we have several issues with platform_get_irq*() APIs?
> 
> 1. The unfortunate naming

unfortunate naming for the currently implemented semantic, yes.

> 2. The vIRQ0 handling: a) WARN() followed by b) returned value 0

I'm happy with the vIRQ0 handling. Today platform_get_irq() and it's
silent variant returns either a valid and usuable irq number or a
negative error value. That's totally fine.

> 3. The specific cookie for "IRQ not found, while no error happened" case

Not sure what you mean here. I have no problem that a situation I can
cope with is called an error for the query function. I just do error
handling and continue happily. So the part "while no error happened" is
irrelevant to me.

Additionally I see the problems:

4. The semantic as implemented in Sergey's patch isn't better than the
current one. platform_get_irq*() is still considerably different from
(clk|gpiod)_get* because the not-found value for the _optional variant
isn't usuable for the irq case. For clk and gpio I get rid of a whole if
branch, for irq I only change the if-condition. (And if that change is
considered good or bad seems to be subjective.)

For the idea to add a warning to platform_get_irq_optional for all but
-ENXIO (and -EPROBE_DEFER), I see the problem:

5. platform_get_irq*() issuing an error message is only correct most of
the time and given proper error handling in the caller (which might be
able to handle not only -ENXIO but maybe also -EINVAL[1]) the error message
is irritating. Today platform_get_irq() emits an error message for all
but -EPROBE_DEFER. As soon as we find a driver that handles -EINVAL we
need a function platform_get_irq_variant1 to be silent for -EINVAL,
-EPROBE_DEFER and -ENXIO (or platform_get_irq_variant2 that is only
silent for -EINVAL and -EPROBE_DEFER?)

IMHO a query function should always be silent and let the caller do the
error handling. And if it's only because

	mydev: IRQ index 0 not found

is worse than

	mydev: neither TX irq not a muxed RX/TX irq found

. Also "index 0" is irritating for devices that are expected to have
only a single irq (i.e. the majority of all devices).

Yes, I admit, we can safe some code by pushing the error message in a
query function. But that doesn't only have advantages.

Best regards
Uwe

[1] Looking through the source I wonder: What are the errors that can happen
    in platform_get_irq*()? (calling everything but a valid irq number
    an error) Looking at many callers, they only seem to expect "not
    found" and some "probe defer" (even platform_get_irq() interprets
    everything but -EPROBE_DEFER as "IRQ index %u not found\n".)
    IMHO before we should consider to introduce a platform_get_irq*()
    variant with improved semantics, some cleanup in the internals of
    the irq lookup are necessary.

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | https://www.pengutronix.de/ |

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