linux-kernel - Re: [PATCH 18/20] clocksource / acpi: Add macro CLOCKSOURCE_ACPI

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Message-ID: <20140124151513.GD19052@arm.com>
Date:	Fri, 24 Jan 2014 15:15:13 +0000
From:	Catalin Marinas <catalin.marinas@....com>
To:	Mark Rutland <mark.rutland@....com>
Cc:	Hanjun Guo <hanjun.guo@...aro.org>,
	Linus Walleij <linus.walleij@...aro.org>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Will Deacon <Will.Deacon@....com>,
	Russell King - ARM Linux <linux@....linux.org.uk>,
	ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"grant.likely@...aro.org" <grant.likely@...aro.org>,
	Matthew Garrett <mjg59@...f.ucam.org>,
	Olof Johansson <olof@...om.net>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Rob Herring <robh@...nel.org>, Arnd Bergmann <arnd@...db.de>,
	Patch Tracking <patches@...aro.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	linaro-kernel <linaro-kernel@...ts.linaro.org>,
	"linaro-acpi@...ts.linaro.org" <linaro-acpi@...ts.linaro.org>,
	Charles Garcia-Tobin <Charles.Garcia-Tobin@....com>,
	Amit Daniel Kachhap <amit.daniel@...sung.com>
Subject: Re: [PATCH 18/20] clocksource / acpi: Add macro
 CLOCKSOURCE_ACPI_DECLARE

On Fri, Jan 24, 2014 at 12:08:15PM +0000, Mark Rutland wrote:
> On Fri, Jan 24, 2014 at 12:20:46AM +0000, Hanjun Guo wrote:
> > On 2014年01月22日 19:45, Mark Rutland wrote:
> > > On Wed, Jan 22, 2014 at 08:26:50AM +0000, Linus Walleij wrote:
> > >> On Fri, Jan 17, 2014 at 1:25 PM, Hanjun Guo <hanjun.guo@...aro.org> wrote:
> > >>
> > >>> From: Amit Daniel Kachhap <amit.daniel@...sung.com>
> > >>>
> > >>> This macro does the same job as CLOCKSOURCE_OF_DECLARE. The device
> > >>> name from the ACPI timer table is matched with all the registered
> > >>> timer controllers and matching initialisation routine is invoked.
> > >>>
> > >>> Signed-off-by: Amit Daniel Kachhap <amit.daniel@...sung.com>
> > >>> Signed-off-by: Hanjun Guo <hanjun.guo@...aro.org>
> > >> Actually I have a fat patch renaming CLOCKSOURCE_OF_DECLARE()
> > >> to TIMER_OF_DECLARE() and I think this macro, if needed, should
> > >> be named TIMER_ACPI_DECLARE().
> > >>
> > >> The reason is that "clocksource" is a Linux-internal name and this
> > >> macro pertains to the hardware name in respective system
> > >> description type.
> > >>
> > >>> +#ifdef CONFIG_ACPI
> > >>> +#define CLOCKSOURCE_ACPI_DECLARE(name, compat, fn)                     \
> > >>> +       static const struct acpi_device_id __clksrc_acpi_table_##name   \
> > >>> +               __used __section(__clksrc_acpi_table)                   \
> > >>> +                = { .id = compat,                              \
> > >>> +                    .driver_data = (kernel_ulong_t)fn }
> > >>> +#else
> > >>> +#define CLOCKSOURCE_ACPI_DECLARE(name, compat, fn)
> > >>> +#endif
> > >> This hammers down the world to compile one binary for ACPI
> > >> and one binary for device tree. Maybe that's fine, I don't know.
> > > How does it do that?
> > >
> > > As far as I could tell CONFIG_ACPI and CONFIG_OF are not mutually
> > > exclusive, and this just means that we only build the datastructures for
> > > matching from ACPI when CONFIG_ACPI is enabled.
> > >
> > > Have I missed something?
> > >
> > > I definitely don't want to see mutually exclusive ACPI and DT support.
> > 
> > ACPI and DT did the same job so I think they should mutually exclusive.
> > if we enable both DT and ACPI in one system, this will leading confusions.
> 
> ACPI and DT do similar jobs, and we should be mutually exclusive at
> runtime. However, they should not be mutually exclusive at compile-time.
> 
> Being mutually exclusive at compile-time is just broken. It creates more
> work for distributions (who need to ship double the number of kernels),
> it increases the number of configurations requiring testing, and it
> makes it easier for bugs to be introduced. It's just painful, and
> there's no reason for it.

I fully agree (IOW, I'll NAK patches that break this assumption; we want
single kernel image whether it uses DT or ACPI).

> At boot time the kernel needs to decide which to use for hardware
> description, and completely ignore the other (which should not be
> present, but lets not assume that or inevitably someone will break that
> assumption for a quick hack).
> 
> The same kernel should boot on a system that has a DTB or a system that
> has ACPI tables. On a system that's provided both it should use one or
> the other, but not both.

Do we still need the chosen node to be passed via DT for command line,
even if the kernel uses ACPI?

-- 
Catalin
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