linux-kernel - Re: [PATCH v4 25/25] coresight: Add support for v8.4 SelfHosted tracing

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Message-ID: <20201119172243.GF4376@gaia>
Date:   Thu, 19 Nov 2020 17:22:43 +0000
From:   Catalin Marinas <catalin.marinas@....com>
To:     Suzuki K Poulose <suzuki.poulose@....com>
Cc:     linux-arm-kernel@...ts.infradead.org, mathieu.poirier@...aro.org,
        mike.leach@...aro.org, linux-kernel@...r.kernel.org,
        anshuman.khandual@....com, jonathan.zhouwen@...wei.com,
        coresight@...ts.linaro.org, Will Deacon <will@...nel.org>
Subject: Re: [PATCH v4 25/25] coresight: Add support for v8.4 SelfHosted
 tracing

On Thu, Nov 19, 2020 at 04:45:47PM +0000, Suzuki K Poulose wrote:
> From: Jonathan Zhou <jonathan.zhouwen@...wei.com>
> 
> v8.4 tracing extensions added support for trace filtering controlled
> by TRFCR_ELx. This must be programmed to allow tracing at EL1/EL2 and
> EL0. The timestamp used is the virtual time. Also enable CONTEXIDR_EL2
> tracing if we are running the kernel at EL2.
> 
> Cc: Catalin Marinas <catalin.marinas@....com>
> Cc: Mathieu Poirier <mathieu.poirier@...aro.org>
> Cc: Mike Leach <mike.leach@...aro.org>
> Cc: Will Deacon <will@...nel.org>
> Signed-off-by: Jonathan Zhou <jonathan.zhouwen@...wei.com>
> [ Move the trace filtering setup etm_init_arch_data() and
>  clean ups]
> Signed-off-by: Suzuki K Poulose <suzuki.poulose@....com>
> ---
>  .../coresight/coresight-etm4x-core.c          | 25 +++++++++++++++++++
>  1 file changed, 25 insertions(+)
> 
> diff --git a/drivers/hwtracing/coresight/coresight-etm4x-core.c b/drivers/hwtracing/coresight/coresight-etm4x-core.c
> index 1d054d2ab2a0..647685736134 100644
> --- a/drivers/hwtracing/coresight/coresight-etm4x-core.c
> +++ b/drivers/hwtracing/coresight/coresight-etm4x-core.c
> @@ -760,6 +760,30 @@ static bool etm4_init_csdev_access(struct etmv4_drvdata *drvdata,
>  	return false;
>  }
>  
> +static void cpu_enable_tracing(void)
> +{
> +	u64 dfr0 = read_sysreg(id_aa64dfr0_el1);
> +	u64 trfcr;
> +
> +	if (!(dfr0 >> ID_AA64DFR0_TRACE_FILT_SHIFT))
> +		return;

What if we get a new field at position 44 while the FILT one at 40 is 0?
We should use cpuid_feature_extract_field() here.

BTW, can this function not go in the cpufeature.c code?

-- 
Catalin