linux-kernel - Re: [PATCH v4 20/25] coresight: etm4x: Detect system instructions support

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Date:   Mon, 23 Nov 2020 09:39:43 +0000
From:   Suzuki K Poulose <suzuki.poulose@....com>
To:     Tingwei Zhang <tingweiz@...eaurora.org>
Cc:     linux-arm-kernel@...ts.infradead.org, anshuman.khandual@....com,
        coresight@...ts.linaro.org, linux-kernel@...r.kernel.org,
        jonathan.zhouwen@...wei.com, mike.leach@...aro.org
Subject: Re: [PATCH v4 20/25] coresight: etm4x: Detect system instructions
 support

On 11/23/20 7:58 AM, Tingwei Zhang wrote:
> Hi Suzuki,
> 
> On Fri, Nov 20, 2020 at 12:45:42AM +0800, Suzuki K Poulose wrote:
>> ETM v4.4 onwards adds support for system instruction access
>> to the ETM. Detect the support on an ETM and switch to using the
>> mode when available.
>>
>> Cc: Mike Leach <mike.leach@...aro.org>
>> Reviewed-by: Mathieu Poirier <mathieu.poirier@...aro.org>
>> Signed-off-by: Suzuki K Poulose <suzuki.poulose@....com>
>> ---
>>   .../coresight/coresight-etm4x-core.c          | 39 +++++++++++++++++++
>>   1 file changed, 39 insertions(+)
>>
>> diff --git a/drivers/hwtracing/coresight/coresight-etm4x-core.c
>> b/drivers/hwtracing/coresight/coresight-etm4x-core.c
>> index 7ac0a185c146..5cbea9c27f58 100644
>> --- a/drivers/hwtracing/coresight/coresight-etm4x-core.c
>> +++ b/drivers/hwtracing/coresight/coresight-etm4x-core.c
>> @@ -684,6 +684,37 @@ static const struct coresight_ops etm4_cs_ops = {
>>   	.source_ops	= &etm4_source_ops,
>>   };
>>
>> +static inline bool cpu_supports_sysreg_trace(void)
>> +{
>> +	u64 dfr0 = read_sysreg_s(SYS_ID_AA64DFR0_EL1);
>> +
>> +	return ((dfr0 >> ID_AA64DFR0_TRACEVER_SHIFT) & 0xfUL) > 0;
>> +}
>> +
>> +static bool etm4_init_sysreg_access(struct etmv4_drvdata *drvdata,
>> +				    struct csdev_access *csa)
>> +{
>> +	u32 devarch;
>> +
>> +	if (!cpu_supports_sysreg_trace())
>> +		return false;
>> +
>> +	/*
>> +	 * ETMs implementing sysreg access must implement TRCDEVARCH.
>> +	 */
>> +	devarch = read_etm4x_sysreg_const_offset(TRCDEVARCH);
>> +	if ((devarch & ETM_DEVARCH_ID_MASK) != ETM_DEVARCH_ETMv4x_ARCH)
> 
> Is this driver suppose to work on ETM 5.0/ETE trace unit before ETE driver
> is ready?

No, it is not supposed to work on an ETE without the ETE support. That check
ensures that we only detect ETMv4x for now. The ETE driver support adds the
ETE_ARCH as one of the supported ETMs. If you hack around it might still probe,
but things could go terribly wrong if we access registers that are not available
on ETE.

Btw, are you able to test this series on an ETMv4.4+ system ?

Kind regards
Suzuki