Re: [Qemu-devel] [PATCH v5 11/37] target-arm: Don't mention PMU in debug feature register

[Christopher Covington <cov@codeaurora.org>]

Hi Peter,

On 03/28/2014 12:09 PM, Peter Maydell wrote:
> Suppress the ID_AA64DFR0_EL1 PMUVer field, even if the CPU specific
> value claims that it exists. QEMU doesn't currently implement it,
> and not advertising it prevents the guest from trying to use it
> and getting UNDEFs on unimplemented registers.
> 
> Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
> Reviewed-by: Peter Crosthwaite <peter.crosthwaite@xilinx.com>
> ---
> This is arguably a hack, but otherwise Linux tries to prod
> half a dozen PMU sysregs.
> ---
>  target-arm/helper.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/target-arm/helper.c b/target-arm/helper.c
> index 4b6c1b6..62f7fd3 100644
> --- a/target-arm/helper.c
> +++ b/target-arm/helper.c
> @@ -2036,7 +2036,12 @@ void register_cp_regs_for_features(ARMCPU *cpu)
>              { .name = "ID_AA64DFR0_EL1", .state = ARM_CP_STATE_AA64,
>                .opc0 = 3, .opc1 = 0, .crn = 0, .crm = 5, .opc2 = 0,
>                .access = PL1_R, .type = ARM_CP_CONST,
> -              .resetvalue = cpu->id_aa64dfr0 },
> +              /* We mask out the PMUVer field, beacuse we don't currently
> +               * implement the PMU. Not advertising it prevents the guest
> +               * from trying to use it and getting UNDEFs on registers we
> +               * don't implement.
> +               */
> +              .resetvalue = cpu->id_aa64dfr0 & ~0xf00 },
>              { .name = "ID_AA64DFR1_EL1", .state = ARM_CP_STATE_AA64,
>                .opc0 = 3, .opc1 = 0, .crn = 0, .crm = 5, .opc2 = 1,
>                .access = PL1_R, .type = ARM_CP_CONST,

Is the A32 port able to communicate the instruction count to target software
via the PMU?

Thanks,
Christopher

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