[Buildroot] [PATCH 07/24 v4] manual: document dependencies on atomic operations

[Yann E. MORIN <yann.morin.1998@free.fr>]

Thomas, All,

On 2014-08-17 15:01 +0200, Thomas De Schampheleire spake thusly:
> "Yann E. MORIN" <yann.morin.1998@free.fr> schreef:
> >From: Anton Kolesov <anton.kolesov@synopsys.com>
> >
> >Add atomic operations to the list of generic dependencies.
> >
> >Since this is an architecture option, there is no comment string to be
> >added.
> >
> >Signed-off-by: Anton Kolesov <Anton.Kolesov@synopsys.com>
> >[yann.morin.1998 at free.fr: use the new arch-option; remove comment string]
> >Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
> >---
> > docs/manual/adding-packages-directory.txt | 4 ++++
> > 1 file changed, 4 insertions(+)
> >
> >diff --git a/docs/manual/adding-packages-directory.txt b/docs/manual/adding-packages-directory.txt
> >index 93e6a3e..40a81d5 100644
> >--- a/docs/manual/adding-packages-directory.txt
> >+++ b/docs/manual/adding-packages-directory.txt
> >@@ -219,6 +219,10 @@ use in the comment.
> > ** Dependency symbol: +BR2_USE_MMU+
> > ** Comment string: no comment to be added
> > 
> >+* Atomic operations
> >+** Dependency symbol: +BR2_ARCH_HAS_ATOMICS+
> >+** Comment string: no comment to be added
> >+
> 
> Should we provide a brief explanation, reference, or
>  name of these functions to make it a bit clearer what
> is meant with 'atomic operations'?

Well, the atomics are all named differently in different architectures.

For example, armv6+ has LDREX and STREX (amon others):
    http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.dht0008a/ch01s02s01.html

While on x86, I don't think there are corresponding instructions, but
you can prefix some intructions with the LOCK prefix to achieve a
similar result.

So, I would not know what to put in here. Also, we do not explain what
the other options are (like MMU, for example). Why would we do that for
this specific option, and not others?

Regards,
Yann E. MORIN.

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