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Groups > linux.kernel > #1346768 > unrolled thread

[PATCH 1/6] rtc: generic: allow building on all architectures

Started byArnd Bergmann <arnd@arndb.de>
First post2016-03-01 18:10 +0100
Last post2016-03-02 10:40 +0100
Articles 5 — 3 participants

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  [PATCH 1/6] rtc: generic: allow building on all architectures Arnd Bergmann <arnd@arndb.de> - 2016-03-01 18:10 +0100
    Re: [PATCH 1/6] rtc: generic: allow building on all architectures Geert Uytterhoeven <geert@linux-m68k.org> - 2016-03-02 10:00 +0100
      Re: [PATCH 1/6] rtc: generic: allow building on all architectures Arnd Bergmann <arnd@arndb.de> - 2016-03-02 10:10 +0100
      Re: [PATCH 1/6] rtc: generic: allow building on all architectures Andreas Schwab <schwab@linux-m68k.org> - 2016-03-02 10:30 +0100
        Re: [PATCH 1/6] rtc: generic: allow building on all architectures Geert Uytterhoeven <geert@linux-m68k.org> - 2016-03-02 10:40 +0100

#1346768 — [PATCH 1/6] rtc: generic: allow building on all architectures

FromArnd Bergmann <arnd@arndb.de>
Date2016-03-01 18:10 +0100
Subject[PATCH 1/6] rtc: generic: allow building on all architectures
Message-ID<r7VY6-3zV-33@gated-at.bofh.it>
There are four architectures using this driver, but since we can
build it with COMPILE_TEST, we should try dealing with the absence
of the asm/rtc.h header file, to avoid getting a build error:

drivers/rtc/rtc-generic.c:12:21: fatal error: asm/rtc.h: No such file or directory

This creates an alternative use of the driver, allowing architectures
to pass a set of rtc_class_ops in platform data. We can convert the
four architectures to use this and then remove the original
code.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
---
 drivers/rtc/rtc-generic.c | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/drivers/rtc/rtc-generic.c b/drivers/rtc/rtc-generic.c
index e782ebd719b2..d726c6aa96a8 100644
--- a/drivers/rtc/rtc-generic.c
+++ b/drivers/rtc/rtc-generic.c
@@ -9,6 +9,8 @@
 #include <linux/platform_device.h>
 #include <linux/rtc.h>
 
+#if defined(CONFIG_M68K) || defined(CONFIG_PARISC) || \
+    defined(CONFIG_PPC) || defined(CONFIG_SUPERH32)
 #include <asm/rtc.h>
 
 static int generic_get_time(struct device *dev, struct rtc_time *tm)
@@ -33,13 +35,21 @@ static const struct rtc_class_ops generic_rtc_ops = {
 	.read_time = generic_get_time,
 	.set_time = generic_set_time,
 };
+#else
+#define generic_rtc_ops *(struct rtc_class_ops*)NULL
+#endif
 
 static int __init generic_rtc_probe(struct platform_device *dev)
 {
 	struct rtc_device *rtc;
+	const struct rtc_class_ops *ops;
+
+	ops = dev_get_platdata(&dev->dev);
+	if (!ops)
+		ops = &generic_rtc_ops;
 
 	rtc = devm_rtc_device_register(&dev->dev, "rtc-generic",
-					&generic_rtc_ops, THIS_MODULE);
+					ops, THIS_MODULE);
 	if (IS_ERR(rtc))
 		return PTR_ERR(rtc);
 
-- 
2.7.0

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#1347863

FromGeert Uytterhoeven <geert@linux-m68k.org>
Date2016-03-02 10:00 +0100
Message-ID<r8aNs-5fM-17@gated-at.bofh.it>
In reply to#1346768
Hi Arnd,

On Tue, Mar 1, 2016 at 5:59 PM, Arnd Bergmann <arnd@arndb.de> wrote:
> There are four architectures using this driver, but since we can
> build it with COMPILE_TEST, we should try dealing with the absence
> of the asm/rtc.h header file, to avoid getting a build error:
>
> drivers/rtc/rtc-generic.c:12:21: fatal error: asm/rtc.h: No such file or directory
>
> This creates an alternative use of the driver, allowing architectures
> to pass a set of rtc_class_ops in platform data. We can convert the
> four architectures to use this and then remove the original
> code.
>
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
> ---
>  drivers/rtc/rtc-generic.c | 12 +++++++++++-
>  1 file changed, 11 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/rtc/rtc-generic.c b/drivers/rtc/rtc-generic.c
> index e782ebd719b2..d726c6aa96a8 100644
> --- a/drivers/rtc/rtc-generic.c
> +++ b/drivers/rtc/rtc-generic.c
> @@ -9,6 +9,8 @@
>  #include <linux/platform_device.h>
>  #include <linux/rtc.h>
>
> +#if defined(CONFIG_M68K) || defined(CONFIG_PARISC) || \
> +    defined(CONFIG_PPC) || defined(CONFIG_SUPERH32)
>  #include <asm/rtc.h>
>
>  static int generic_get_time(struct device *dev, struct rtc_time *tm)
> @@ -33,13 +35,21 @@ static const struct rtc_class_ops generic_rtc_ops = {
>         .read_time = generic_get_time,
>         .set_time = generic_set_time,
>  };
> +#else
> +#define generic_rtc_ops *(struct rtc_class_ops*)NULL
> +#endif
>
>  static int __init generic_rtc_probe(struct platform_device *dev)
>  {
>         struct rtc_device *rtc;
> +       const struct rtc_class_ops *ops;
> +
> +       ops = dev_get_platdata(&dev->dev);
> +       if (!ops)
> +               ops = &generic_rtc_ops;

I hope no compiler version treats "&*(struct rtc_class_ops*)NULL" as
undefined behavior?

>
>         rtc = devm_rtc_device_register(&dev->dev, "rtc-generic",
> -                                       &generic_rtc_ops, THIS_MODULE);
> +                                       ops, THIS_MODULE);
>         if (IS_ERR(rtc))
>                 return PTR_ERR(rtc);

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

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#1347867

FromArnd Bergmann <arnd@arndb.de>
Date2016-03-02 10:10 +0100
Message-ID<r8aX8-5yy-13@gated-at.bofh.it>
In reply to#1347863
On Wednesday 02 March 2016 09:57:27 Geert Uytterhoeven wrote:
> > @@ -33,13 +35,21 @@ static const struct rtc_class_ops generic_rtc_ops = {
> >         .read_time = generic_get_time,
> >         .set_time = generic_set_time,
> >  };
> > +#else
> > +#define generic_rtc_ops *(struct rtc_class_ops*)NULL
> > +#endif
> >
> >  static int __init generic_rtc_probe(struct platform_device *dev)
> >  {
> >         struct rtc_device *rtc;
> > +       const struct rtc_class_ops *ops;
> > +
> > +       ops = dev_get_platdata(&dev->dev);
> > +       if (!ops)
> > +               ops = &generic_rtc_ops;
> 
> I hope no compiler version treats "&*(struct rtc_class_ops*)NULL" as
> undefined behavior?

It's a bit odd, but I think it's syntactically correct C, and not
much too different from 

#define offsetof(TYPE, MEMBER)  ((size_t)&((TYPE *)0)->MEMBER)

is it? My last patch gets rid of it again.

	Arnd

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#1347877

FromAndreas Schwab <schwab@linux-m68k.org>
Date2016-03-02 10:30 +0100
Message-ID<r8bgu-5FN-9@gated-at.bofh.it>
In reply to#1347863
Geert Uytterhoeven <geert@linux-m68k.org> writes:

>> +#else
>> +#define generic_rtc_ops *(struct rtc_class_ops*)NULL
>> +#endif
>>
>>  static int __init generic_rtc_probe(struct platform_device *dev)
>>  {
>>         struct rtc_device *rtc;
>> +       const struct rtc_class_ops *ops;
>> +
>> +       ops = dev_get_platdata(&dev->dev);
>> +       if (!ops)
>> +               ops = &generic_rtc_ops;
>
> I hope no compiler version treats "&*(struct rtc_class_ops*)NULL" as
> undefined behavior?

Yes, that is guaranteed, the operations cancel each other (6.5.3.2#3: If
the operand is the result of a unary * operator, neither that operator
nor the & operator is evaluated and the result is as if both were
omitted).

Andreas.

-- 
Andreas Schwab, schwab@linux-m68k.org
GPG Key fingerprint = 58CA 54C7 6D53 942B 1756  01D3 44D5 214B 8276 4ED5
"And now for something completely different."

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#1347888

FromGeert Uytterhoeven <geert@linux-m68k.org>
Date2016-03-02 10:40 +0100
Message-ID<r8bqb-5KC-17@gated-at.bofh.it>
In reply to#1347877
On Wed, Mar 2, 2016 at 10:28 AM, Andreas Schwab <schwab@linux-m68k.org> wrote:
> Geert Uytterhoeven <geert@linux-m68k.org> writes:
>
>>> +#else
>>> +#define generic_rtc_ops *(struct rtc_class_ops*)NULL
>>> +#endif
>>>
>>>  static int __init generic_rtc_probe(struct platform_device *dev)
>>>  {
>>>         struct rtc_device *rtc;
>>> +       const struct rtc_class_ops *ops;
>>> +
>>> +       ops = dev_get_platdata(&dev->dev);
>>> +       if (!ops)
>>> +               ops = &generic_rtc_ops;
>>
>> I hope no compiler version treats "&*(struct rtc_class_ops*)NULL" as
>> undefined behavior?
>
> Yes, that is guaranteed, the operations cancel each other (6.5.3.2#3: If
> the operand is the result of a unary * operator, neither that operator
> nor the & operator is evaluated and the result is as if both were
> omitted).

Thanks for confirming.

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

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