linux-kernel - Re: [RFC 06/11] coresight: ete: Detect ETE as one of the supported ETMs

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Date:   Mon, 23 Nov 2020 09:56:28 +0000
From:   Suzuki K Poulose <suzuki.poulose@....com>
To:     Tingwei Zhang <tingweiz@...eaurora.org>,
        Anshuman Khandual <anshuman.khandual@....com>
Cc:     coresight@...ts.linaro.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, mike.leach@...aro.org
Subject: Re: [RFC 06/11] coresight: ete: Detect ETE as one of the supported
 ETMs

Hi Tingwei,


On 11/14/20 5:36 AM, Tingwei Zhang wrote:
> Hi Anshuman,
> 
> On Tue, Nov 10, 2020 at 08:45:04PM +0800, Anshuman Khandual wrote:
>> From: Suzuki K Poulose <suzuki.poulose@....com>
>>
>> Add ETE as one of the supported device types we support
>> with ETM4x driver. The devices are named following the
>> existing convention as ete<N>.
>>
>> ETE mandates that the trace resource status register is programmed
>> before the tracing is turned on. For the moment simply write to
>> it indicating TraceActive.
>>
>> Signed-off-by: Suzuki K Poulose <suzuki.poulose@....com>
>> Signed-off-by: Anshuman Khandual <anshuman.khandual@....com>
>> ---

>> @@ -1742,6 +1758,19 @@ static int etm4_probe(struct device *dev, void
>> __iomem *base)
>>   	if (!desc.access.io_mem ||
>>   	    fwnode_property_present(dev_fwnode(dev), "qcom,skip-power-up"))
>>   		drvdata->skip_power_up = true;
>> +	major = ETM_ARCH_MAJOR_VERSION(drvdata->arch);
>> +	minor = ETM_ARCH_MINOR_VERSION(drvdata->arch);
>> +	if (drvdata->arch >= ETM_ARCH_ETE) {
>> +		type_name = "ete";
>> +		major -= 4;
>> +	} else {
>> +		type_name = "etm";
>> +	}
>> +
> When trace unit supports ETE, could it be still compatible with ETMv4.4?
> Can use selectively use it as ETM instead of ETE?

No. Even though most of the register sets are compatible, there are additional
restrictions and some new rules for the ETE. So, when you treat the ETE as an
ETMv4.4, you could be treading into "UNPREDICTABLE" behaviors.

Suzuki