lkml.org 
[lkml]   [2018]   [Feb]   [7]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH 2/2] arm64: Expose Arm v8.4 features
On Wed, Feb 07, 2018 at 10:51:55AM +0000, Suzuki K Poulose wrote:
> On 07/02/18 10:43, Dave Martin wrote:
> >On Thu, Feb 01, 2018 at 10:38:38AM +0000, Suzuki K Poulose wrote:
> >>Expose the new features introduced by Arm v8.4 extensions to
> >>Arm v8-A profile.
> >>
> >>These include :
> >>
> >> 1) Data indpendent timing of instructions. (DIT, exposed as HWCAP_DIT)
> >> 2) Unaligned atomic instructions and Single-copy atomicity of loads
> >> and stores. (AT, expose as HWCAP_USCAT)
> >> 3) LDAPR and STLR instructions with immediate offsets (extension to
> >> LRCPC, exposed as HWCAP_ILRCPC)
> >> 4) Flag manipulation instructions (TS, exposed as HWCAP_FLAGM).
> >>
> >>While at it get rid of the RES0 entries in the cpu-feature-registers.txt
> >>documentation.
> >
> >Should we write somewhere than fields that are not described here are
> >implicitly RES0, or would that be too strong a statement?
>
> Dave,
>
> We already have the following description in the file :
>
> "The following rules are applied to the value returned by the
> infrastructure:
>
> a) The value of an 'IMPLEMENTATION DEFINED' field is set to 0.
> b) The value of a reserved field is populated with the reserved
> value as defined by the architecture.
> c) The value of a 'visible' field holds the system wide safe value
> for the particular feature (except for MIDR_EL1, see section 4).
> d) All other fields (i.e, invisible fields) are set to indicate
> the feature is missing (as defined by the architecture).
> "
>
> So we don't have to bother if the fields are RES0 or they get
> some definitions in the future, as long as we don't expose them.

Agreed, that does seem sufficient:

Reviewed-by: Dave Martin <Dave.Martin@arm.com>

[...]

Cheers
---Dave

\
 
 \ /
  Last update: 2018-02-07 12:56    [W:0.052 / U:0.144 seconds]
©2003-2018 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site