From: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
To: "Rafael J. Wysocki" <rafael@kernel.org>
Cc: "Geert Uytterhoeven" <geert@linux-m68k.org>,
"Andrew Lunn" <andrew@lunn.ch>,
"Uwe Kleine-König" <u.kleine-koenig@pengutronix.de>,
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Subject: Re: [PATCH 1/2] platform: make platform_get_irq_optional() optional
Date: Wed, 12 Jan 2022 18:21:26 +0200 [thread overview]
Message-ID: <Yd8ABkwagyVevTaE@smile.fi.intel.com> (raw)
In-Reply-To: <CAJZ5v0iyAHtDe1kFObQorXOX0Xraxac0j29Dh+8sq7zxzbsmcQ@mail.gmail.com>
On Wed, Jan 12, 2022 at 03:41:38PM +0100, Rafael J. Wysocki wrote:
> On Wed, Jan 12, 2022 at 2:55 PM Geert Uytterhoeven <geert@linux-m68k.org> wrote:
> >
> > Hi Andrew,
> >
> > On Wed, Jan 12, 2022 at 2:38 PM Andrew Lunn <andrew@lunn.ch> wrote:
> > > > If an optional IRQ is not present, drivers either just ignore it (e.g.
> > > > for devices that can have multiple interrupts or a single muxed IRQ),
> > > > or they have to resort to polling. For the latter, fall-back handling
> > > > is needed elsewhere in the driver.
> > > > To me it sounds much more logical for the driver to check if an
> > > > optional irq is non-zero (available) or zero (not available), than to
> > > > sprinkle around checks for -ENXIO. In addition, you have to remember
> > > > that this one returns -ENXIO, while other APIs use -ENOENT or -ENOSYS
> > > > (or some other error code) to indicate absence. I thought not having
> > > > to care about the actual error code was the main reason behind the
> > > > introduction of the *_optional() APIs.
> > >
> > > The *_optional() functions return an error code if there has been a
> > > real error which should be reported up the call stack. This excludes
> > > whatever error code indicates the requested resource does not exist,
> > > which can be -ENODEV etc. If the device does not exist, a magic cookie
> > > is returned which appears to be a valid resources but in fact is
> > > not. So the users of these functions just need to check for an error
> > > code, and fail the probe if present.
> >
> > Agreed.
> >
> > Note that in most (all?) other cases, the return type is a pointer
> > (e.g. to struct clk), and NULL is the magic cookie.
> >
> > > You seems to be suggesting in binary return value: non-zero
> > > (available) or zero (not available)
> >
> > Only in case of success. In case of a real failure, an error code
> > must be returned.
> >
> > > This discards the error code when something goes wrong. That is useful
> > > information to have, so we should not be discarding it.
> >
> > No, the error code must be retained in case of failure.
> >
> > > IRQ don't currently have a magic cookie value. One option would be to
> > > add such a magic cookie to the subsystem. Otherwise, since 0 is
> > > invalid, return 0 to indicate the IRQ does not exist.
> >
> > Exactly. And using 0 means the similar code can be used as for other
> > subsystems, where NULL would be returned.
> >
> > The only remaining difference is the "dummy cookie can be passed
> > to other functions" behavior. Which is IMHO a valid difference,
> > as unlike with e.g. clk_prepare_enable(), you do pass extra data to
> > request_irq(), and sometimes you do need to handle the absence of
> > the interrupt using e.g. polling.
> >
> > > The request for a script checking this then makes sense. However, i
> > > don't know how well coccinelle/sparse can track values across function
> > > calls. They probably can check for:
> > >
> > > ret = irq_get_optional()
> > > if (ret < 0)
> > > return ret;
> > >
> > > A missing if < 0 statement somewhere later is very likely to be an
> > > error. A comparison of <= 0 is also likely to be an error. A check for
> > > > 0 before calling any other IRQ functions would be good. I'm
> > > surprised such a check does not already existing in the IRQ API, but
> > > there are probably historical reasons for that.
> >
> > There are still a few platforms where IRQ 0 does exist.
>
> Not just a few even. This happens on a reasonably recent x86 PC:
Yes, but the timer doesn't use platform_get_irq*() and friends.
> rafael@gratch:~/work/linux-pm> head -2 /proc/interrupts
> CPU0 CPU1 CPU2 CPU3 CPU4 CPU5
> 0: 10 0 0 0 0 0
> IR-IO-APIC 2-edge
> timer
--
With Best Regards,
Andy Shevchenko
next prev parent reply other threads:[~2022-01-12 16:27 UTC|newest]
Thread overview: 94+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20220110195449.12448-1-s.shtylyov@omp.ru>
2022-01-10 19:54 ` [PATCH 1/2] platform: make platform_get_irq_optional() optional Sergey Shtylyov
2022-01-10 20:10 ` Uwe Kleine-König
2022-01-10 21:07 ` Andy Shevchenko
2022-01-10 21:44 ` Uwe Kleine-König
2022-01-10 21:18 ` Andrew Lunn
2022-01-12 8:33 ` Geert Uytterhoeven
2022-01-12 8:50 ` Uwe Kleine-König
2022-01-12 10:27 ` Geert Uytterhoeven
2022-01-12 12:27 ` Andy Shevchenko
2022-01-12 13:38 ` Andrew Lunn
2022-01-12 13:51 ` Andy Shevchenko
2022-01-12 13:54 ` Geert Uytterhoeven
2022-01-12 14:41 ` Rafael J. Wysocki
2022-01-12 15:05 ` Sergey Shtylyov
2022-01-12 15:13 ` Hans de Goede
2022-01-12 15:48 ` Rafael J. Wysocki
2022-01-12 16:21 ` Andy Shevchenko [this message]
2022-01-12 21:31 ` Uwe Kleine-König
2022-01-12 21:45 ` Mark Brown
2022-01-13 11:08 ` Uwe Kleine-König
2022-01-13 14:45 ` Mark Brown
2022-01-13 19:43 ` [PATCH] driver core: platform: Rename platform_get_irq_optional() to platform_get_irq_silent() Uwe Kleine-König
2022-01-13 20:17 ` Mark Brown
2022-01-13 20:57 ` Sergey Shtylyov
2022-01-13 22:43 ` Uwe Kleine-König
2022-01-14 9:58 ` Geert Uytterhoeven
2022-01-15 15:21 ` Uwe Kleine-König
2022-01-15 21:06 ` Sergey Shtylyov
2022-01-14 11:34 ` Sergey Shtylyov
2022-01-13 20:31 ` Guenter Roeck
2022-01-13 21:42 ` Florian Fainelli
2022-01-13 23:06 ` Uwe Kleine-König
2022-01-14 17:55 ` Sergey Shtylyov
2022-01-15 13:55 ` Uwe Kleine-König
2022-01-19 18:36 ` Andy Shevchenko
2022-01-19 19:44 ` Sergey Shtylyov
2022-01-19 18:40 ` Andy Shevchenko
2022-01-14 6:57 ` Peter Korsgaard
2022-01-14 13:04 ` Andy Shevchenko
2022-01-15 15:45 ` Uwe Kleine-König
2022-01-19 18:51 ` Andy Shevchenko
2022-01-19 19:47 ` Sergey Shtylyov
2022-01-19 20:55 ` Andy Shevchenko
2022-01-20 7:57 ` Uwe Kleine-König
2022-01-24 15:01 ` Andy Shevchenko
2022-01-24 21:02 ` Sergey Shtylyov
2022-01-25 8:25 ` Geert Uytterhoeven
2022-01-25 12:56 ` Matthias Schiffer
2022-01-25 14:01 ` Andy Shevchenko
2022-01-14 19:45 ` Sergey Shtylyov
2022-01-14 20:29 ` Uwe Kleine-König
2022-01-15 13:08 ` Sergey Shtylyov
2022-01-19 18:52 ` Andy Shevchenko
2022-01-13 20:35 ` [PATCH 1/2] platform: make platform_get_irq_optional() optional Sergey Shtylyov
2022-01-14 9:25 ` Uwe Kleine-König
2022-01-14 9:39 ` Geert Uytterhoeven
2022-01-14 19:14 ` Sergey Shtylyov
2022-01-14 20:22 ` Uwe Kleine-König
2022-01-15 20:22 ` Sergey Shtylyov
2022-01-17 8:41 ` Geert Uytterhoeven
2022-01-17 9:24 ` Uwe Kleine-König
2022-01-17 10:35 ` Geert Uytterhoeven
2022-01-17 11:49 ` Uwe Kleine-König
2022-01-17 13:08 ` Geert Uytterhoeven
2022-01-17 17:06 ` Uwe Kleine-König
2022-01-18 8:25 ` Geert Uytterhoeven
2022-01-18 9:09 ` Uwe Kleine-König
2022-01-18 9:37 ` Geert Uytterhoeven
2022-01-18 12:08 ` Uwe Kleine-König
2022-01-18 12:49 ` Geert Uytterhoeven
2022-01-18 14:29 ` Uwe Kleine-König
2022-01-19 16:12 ` Sergey Shtylyov
2022-01-19 18:29 ` Sergey Shtylyov
2022-01-20 11:27 ` Sergey Shtylyov
2022-01-16 18:15 ` Sergey Shtylyov
2022-01-17 8:47 ` Uwe Kleine-König
2022-01-18 20:21 ` Sergey Shtylyov
2022-01-18 22:26 ` Uwe Kleine-König
2022-01-19 15:34 ` Sergey Shtylyov
2022-01-19 18:58 ` Andy Shevchenko
2022-01-19 19:49 ` Sergey Shtylyov
2022-01-14 18:46 ` Sergey Shtylyov
2022-01-15 18:36 ` [PATCH 1/2] platform: make platform_get_irq_optional() optional (summary) Uwe Kleine-König
2022-01-16 14:19 ` Greg Kroah-Hartman
2022-01-18 9:18 ` Uwe Kleine-König
2022-01-18 9:32 ` Greg Kroah-Hartman
2022-01-19 10:56 ` Sergey Shtylyov
2022-01-19 11:33 ` Uwe Kleine-König
2022-01-19 11:42 ` Sergey Shtylyov
2022-01-19 19:06 ` Andy Shevchenko
2022-01-17 11:57 ` [PATCH 1/2] platform: make platform_get_irq_optional() optional Sergey Shtylyov
2022-01-19 15:02 ` Uwe Kleine-König
2022-01-19 15:50 ` Sergey Shtylyov
2022-01-10 19:54 ` [PATCH 2/2] platform: make platform_get_irq_byname_optional() optional Sergey Shtylyov
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