Re: [PATCH] target/arm: Correct the encoding of MDCCSR_EL0

[Peter Maydell]

On Tue, 29 Jun 2021 at 11:41, Nick Hudson <hnick@vmware.com> wrote:
>
>
>
> > On 29 Jun 2021, at 10:49, Peter Maydell <peter.maydell@linaro.org> wrote:
> >
> > On Tue, 29 Jun 2021 at 09:27, <hnick@vmware.com> wrote:
> >>
> >> Signed-off-by: Nick Hudson <hnick@vmware.com>
> >> ---
> >> target/arm/helper.c | 2 +-
> >> 1 file changed, 1 insertion(+), 1 deletion(-)
> >>
> >> diff --git a/target/arm/helper.c b/target/arm/helper.c
> >> index a66c1f0b9e..7267af7924 100644
> >> --- a/target/arm/helper.c
> >> +++ b/target/arm/helper.c
> >> @@ -6330,7 +6330,7 @@ static const ARMCPRegInfo debug_cp_reginfo[] = {
> >>      * We don't implement the configurable EL0 access.
> >>      */
> >>     { .name = "MDCCSR_EL0", .state = ARM_CP_STATE_BOTH,
> >> -      .cp = 14, .opc0 = 2, .opc1 = 0, .crn = 0, .crm = 1, .opc2 = 0,
> >> +      .cp = 14, .opc0 = 2, .opc1 = 3, .crn = 0, .crm = 1, .opc2 = 0,
> >>       .type = ARM_CP_ALIAS,
> >>       .access = PL1_R, .accessfn = access_tda,
> >>       .fieldoffset = offsetof(CPUARMState, cp15.mdscr_el1), },
> >
> > This fixes the encoding for AArch64, but breaks it for AArch32,
> > where it is cp=14 opc1=0 crn=0 crm=1 opc2=0. Because this is one of
> > those system registers where the AArch64 and AArch32 encodings
> > don't match up, to fix the AArch64 encoding we need to replace
> > this ARM_CP_STATE_BOTH reginfo with separate reginfo for
> > ARM_CP_STATE_AA32 and ARM_CP_STATE_AA64, something like this:
> >
> >    { .name = "MDCCSR_EL0", .state = ARM_CP_STATE_AA64,
> >      .opc0 = 2, .opc1 = 3, .crn = 0, .crm = 1, .opc2 = 0,
> >      .type = ARM_CP_ALIAS,
> >      .access = PL1_R, .accessfn = access_tda,
> >      .fieldoffset = offsetof(CPUARMState, cp15.mdscr_el1), },
> >    { .name = "DBGDSCRint", .state = ARM_CP_STATE_AA32,
> >      .cp = 14, .opc0 = 2, .opc1 = 0, .crn = 0, .crm = 1, .opc2 = 0,
> >      .type = ARM_CP_ALIAS,
> >      .access = PL1_R, .accessfn = access_tda,
> >      .fieldoffset = offsetoflow32(CPUARMState, cp15.mdscr_el1), },
> >
>
> Ah, yes.
>
> As MDCCSR_EL0[30:29] only maps to DBGDSCRint[30:29] maybe it should be all 
> RAZ?

Well, you can't make it all RAZ, because those 2 bits do still
need to be mapped, but I guess in theory yes we should define
read and write accessor functions for AArch64 MDCCSR_EL0 that
mask out everything except [30:29].

thanks
-- PMM