Re: [PATCH 18/20] clocksource / acpi: Add macro CLOCKSOURCE_ACPI_DECLARE

[Hanjun Guo]

On 2014å01æ24æ 23:15, Catalin Marinas wrote:
> 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 2014å01æ22æ 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@xxxxxxxxxx> wrote:
> > > > >
> > > > > > From: Amit Daniel Kachhap <amit.daniel@xxxxxxxxxxx>
> > > > > >
> > > > > > 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@xxxxxxxxxxx>
> > > > > > Signed-off-by: Hanjun Guo <hanjun.guo@xxxxxxxxxx>
> > > > > 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).

I will not break this in next version, because I totally agree with Mark 
too :)

> > 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?

It depends, but I would prefer not. I prefer UEFI+ACPI and then we don't 
need

the chosen node to be passed via DT.

Thanks
Hanjun

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