From: Geert Uytterhoeven <geert@linux-m68k.org>
To: Sergey Shtylyov <s.shtylyov@omp.ru>
Cc: "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: Mon, 17 Jan 2022 09:41:42 +0100 [thread overview]
Message-ID: <CAMuHMdXVbRudGs69f9ZzaP1PXhteDNZiXA658eMFAwP4nr9r3w@mail.gmail.com> (raw)
In-Reply-To: <c9026f17-2b3f-ee94-0ea3-5630f981fbc1@omp.ru>
On Sat, Jan 15, 2022 at 9:22 PM Sergey Shtylyov <s.shtylyov@omp.ru> wrote:
> On 1/14/22 11:22 PM, Uwe Kleine-König wrote:
> > You have to understand that for clk (and regulator and gpiod) NULL is a
> > valid descriptor that can actually be used, it just has no effect. So
> > this is a convenience value for the case "If the clk/regulator/gpiod in
> > question isn't available, there is nothing to do". This is what makes
> > clk_get_optional() and the others really useful and justifies their
> > existence. This doesn't apply to platform_get_irq_optional().
>
> I do understand that. However, IRQs are a different beast with their
> own justifications...
> > clk_get_optional() is sane and sensible for cases where the clk might be
> > absent and it helps you because you don't have to differentiate between
> > "not found" and "there is an actual resource".
> >
> > The reason for platform_get_irq_optional()'s existence is just that
> > platform_get_irq() emits an error message which is wrong or suboptimal
>
> I think you are very wrong here. The real reason is to simplify the
> callers.
Indeed.
Even for clocks, you cannot assume that you can always blindly use
the returned dummy (actually a NULL pointer) to call into the clk
API. While this works fine for simple use cases, where you just
want to enable/disable an optional clock (clk_prepare_enable() and
clk_disable_unprepare()), it does not work for more complex use cases.
Consider a device with multiple clock inputs, some of them optional,
where the device driver has to find, select and configure a suitable
clock to operate at a certain clock frequency. The driver can call
clk_get_rate(NULL) fine, but will always receive a zero rate, so it
has to check for this (regardless of this being a dummy clock or not,
because this could be an unpopulated clock crystal, which would be
described in DT as a (present) fixed-rate clock with clock-frequency
= <0>).
For configuring the clock rate, the driver does need to check
explicitly for the presence of a dummy clock, as clk_set_rate(NULL,
rate) returns 0 ("success"), while obviously it didn't do anything,
and thus configuring the device to use that clock would cause breakage.
You can check if the clock is a real clock or a dummy using
"if (clk) ...".
And you'd use the same pattern with platform_irq_get_optional() if it
would return 0 if the IRQ was not found: "if (irq) ...".
Gr{oetje,eeting}s,
Geert
--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org
In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
-- Linus Torvalds
next prev parent reply other threads:[~2022-01-17 8:42 UTC|newest]
Thread overview: 93+ 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
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 [this message]
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
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