Re: arch/x86/Kconfig selects invalid HAVE_READQ, HAVE_WRITEQ vars

From: Hitoshi Mitake <h.mitake@gmail.com>
To: Ingo Molnar <mingo@elte.hu>
Cc: "H. Peter Anvin" <hpa@zytor.com>,
	Roland Dreier <rdreier@cisco.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	"Robert P. J. Day" <rpjday@crashcourse.ca>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: arch/x86/Kconfig selects invalid HAVE_READQ, HAVE_WRITEQ vars
Date: Tue, 21 Apr 2009 17:57:02 +0900	[thread overview]
Message-ID: <a6b9f31a0904210157w34ffcccbva5afc50f981b3b90@mail.gmail.com> (raw)
In-Reply-To: <20090421084521.GA20459@elte.hu>

On Tue, Apr 21, 2009 at 17:45, Ingo Molnar <mingo@elte.hu> wrote:
>
> * Hitoshi Mitake <h.mitake@gmail.com> wrote:
>
>> On Tue, Apr 21, 2009 at 01:03, Ingo Molnar <mingo@elte.hu> wrote:
>> >
>> > * Hitoshi Mitake <h.mitake@gmail.com> wrote:
>> >
>> >> On Mon, Apr 20, 2009 at 19:53, Ingo Molnar <mingo@elte.hu> wrote:
>> >> >
>> >> > * H. Peter Anvin <hpa@zytor.com> wrote:
>> >> >
>> >> >> Roland Dreier wrote:
>> >> >> >
>> >> >> > Notice that it reads from addr+4 *before* it reads from addr, rather
>> >> >> > than after as in your example (and in fact your example depends on
>> >> >> > undefined compiler semantics, since there is no sequence point between
>> >> >> > the two operands of the | operator).  Now, I don't know that hardware,
>> >> >> > so I don't know if it makes a difference, but the niu example I gave in
>> >> >> > my original email shows that given hardware with clear-on-read
>> >> >> > registers, the order does very much matter.
>> >> >> >
>> >> >>
>> >> >> At least for x86, the order should be low-high, because that is the
>> >> >> order that those two transactions would be seen on a 32-bit bus
>> >> >> downstream from the CPU if the CPU issued a 64-bit transaction.
>> >> >>
>> >> >> The only sane way to handle this as something other than per-driver
>> >> >> hacks would be something like:
>> >> >>
>> >> >> #include <linux/io64.h>               /* Any 64-bit I/O OK */
>> >> >>
>> >> >> #include <linux/io64lh.h>     /* Low-high splitting OK */
>> >> >>
>> >> >> #include <linux/io64hl.h>     /* High-low splitting OK */
>> >> >>
>> >> >> #include <linux/io64atomic.h> /* 64-bit I/O must be atomic */
>> >> >>
>> >> >> ... i.e. letting the driver choose what fallback method it will accept.
>> >> >
>> >> > Yeah - with the default being the natural low-high order.
>> >> >
>> >> > The other argument is that if a driver really wants some rare, oddly
>> >> > different order it should better define its own method that is not
>> >> > named in the same (or in a similar) way as an existing generic API.
>> >> > Otherwise, confusion will ensue.
>> >> I think this is a good way.
>> >> readq/writeq are already in Linus's tree, removing these is not a good idea.
>> >>
>> >> And I've sent the patch to fix a little problem of Kconfig about
>> >> readq/writeq to you.
>> >> http://marc.info/?l=linux-kernel&m=123521109218008&w=2
>> >> Did you notice?
>> >>
>> >> Adding cautions about accessing order or non-atomic to Kconfig's help
>> >> part may be benefit.
>> >
>> > It's better to add add such non-interactive help text as Makefile
>> > comments:
>> >
>> > #
>> > # This option ...
>> > #
>> >
>> > and they should be invisible in make menuconfig. This is a facility
>> > provided by architectures.
>> I'll move the help text from Kconfig to Makefile.
>> (My original patch also doesn't make help text visible in make menuconfig.)
>
> sorry i meant the Kconfig file - you can put comments in there too.
> help text is really meant for things that are interactive.

Can I think that I should add help text to both of Kconfig and Makefile?
(I'm not a native English speaker, and I'm not good at English.
I'm sorry if I misunderstand something...)