Re: [Xen-devel] [PATCH v2 16/24] xen/arm: page: Use ARMv8 naming to improve readability

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Thu, 21 Sep 2017, Julien Grall wrote:
> Hi,
> 
> On 20/09/17 00:45, Stefano Stabellini wrote:
> > > diff --git a/xen/include/asm-arm/page.h b/xen/include/asm-arm/page.h
> > > index 30fcfa0778..899fd1801a 100644
> > > --- a/xen/include/asm-arm/page.h
> > > +++ b/xen/include/asm-arm/page.h
> > > @@ -26,14 +26,14 @@
> > >    * LPAE entry; the 8-bit fields are packed little-endian into MAIR0 and
> > > MAIR1.
> > >    *
> > >    *                    ai    encoding
> > > - *   MT_UNCACHED      000   0000 0000  -- Strongly Ordered
> > > - *   MT_BUFFERABLE    001   0100 0100  -- Non-Cacheable
> > > - *   MT_WRITETHROUGH  010   1010 1010  -- Write-through
> > > - *   MT_WRITEBACK     011   1110 1110  -- Write-back
> > > - *   MT_DEV_SHARED    100   0000 0100  -- Device
> > > + *   MT_DEVICE_nGnRE  000   0000 0000  -- Strongly Ordered/Device nGnRnE
> > 
> > I admit I always hated the "nGnRE" acronym. However, it is on the ARM
> > ARM too, so if you'd like to introduce it here, I'll accept it. But
> > please at least expand the acronym in the comment to make it
> > understandable (same with nGnRnE).
> 
> "nGnRE" acronym are not great but convey the meaning of what would be the
> resulting attribute.

This is an honest question, no pun intended: how do they convey the
meaning? Personally, I have to look it up every time on the ARM ARM...


> For instance MT_UNCACHED does not really say if it is for
> device or memory. Lets not even mention MT_BUFFERABLE which is in fact
> non-cacheable memory :).
> 
> > 
> > Also, the comment say "nGnRnE" while the definition is MT_DEVICE_nGnRE.
> 
> Actually, the comment is correct but not the naming. It should
> MT_DEVICE_nGnRnE. I will rename it.
> 
> Aside that, I think the comment is understandable. nGnRnE is equivalent to
> Strongly ordered. I could expand nGnRnE (non-Gatherable, non-Reordering, No
> Early write acknowledgment) but I feel at this stage you can just search the
> name in the ARM ARM...

I am not asking to expland the name, only to expand nGnRnE in the
comment on the side. Searching through that pdf is not really a fun
activity.

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