[PATCH v2 06/22] arm64: sys_reg: Define System register encoding
catalin.marinas at arm.com
Thu Oct 8 07:43:48 PDT 2015
On Wed, Oct 07, 2015 at 06:03:34PM +0100, Suzuki K. Poulose wrote:
> On 07/10/15 17:36, Catalin Marinas wrote:
> >On Mon, Oct 05, 2015 at 06:01:55PM +0100, Suzuki K. Poulose wrote:
> >> * (Ref: ARMv8 ARM, Section: "System instruction class encoding overview",
> >> * C5.2, version:ARM DDI 0487A.f)
> >> * [20-19] : Op0
> >>@@ -34,15 +34,40 @@
> >> * [15-12] : CRn
> >> * [11-8] : CRm
> >> * [7-5] : Op2
> >>+ * Hence we use [ sys_reg() << 5 ] in the mrs/msr instructions.
> >Do we really need to have all the ids shifted right by 5? I can't see
> >where it helps. OTOH, it makes the code more complicated by having to
> >remember to shift the id left by 5.
> This is a cosmetic change, to reuse the sys_reg() definitions for both
> mrs_s/msr_s macros and the CPU ID. The (existing)left shift is only needed
> for the mrs_s/msr_s, so the existing users don't have to worry about the shift
> unless they have hard-open-coded values for the register. On the plus
> side it becomes slightly easier to use the same encoding for CPU id
> tracking (and manual decoding). If you think this is superfluous, I could
> change the CPU-id to use right shifted values from sys_reg.
You may be right but I still fail to see whether the shifted values are
useful to the CPUID code. Are you referring to the 'switch' statements?
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