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

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Message-ID: <bd1cf9ec-eeeb-90a1-beb8-23a39dfa3b2a@arm.com>
Date:   Tue, 24 Nov 2020 11:38:55 +0000
From:   Suzuki K Poulose <suzuki.poulose@....com>
To:     Tingwei Zhang <tingweiz@...eaurora.org>
Cc:     anshuman.khandual@....com, coresight@...ts.linaro.org,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        jonathan.zhouwen@...wei.com, mike.leach@...aro.org
Subject: Re: [PATCH v4 20/25] coresight: etm4x: Detect system instructions
 support

On 11/24/20 12:41 AM, Tingwei Zhang wrote:
> On Mon, Nov 23, 2020 at 05:39:43PM +0800, Suzuki K Poulose wrote:
>> 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 ?
>>
> I'm trying to test this series on an ETE. Look like it's not correct.
> I'll apply ETE patch on top of this and test.
> 

Yes please ! Much appreciated. Do you have a TRBE as well ? Or are you
using a legacy CoreSight topology ?

Kind regards
Suzuki