linux-kernel - Re: [PATCH v2] coresight: etm4x: Fix crash observed on Qcom ETM parts with 'Low power override'

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Message-ID: <0b1e6679-62c4-270f-b086-13f3af1ea8e9@arm.com>
Date:   Mon, 7 Nov 2022 16:44:13 +0000
From:   Suzuki K Poulose <suzuki.poulose@....com>
To:     Leo Yan <leo.yan@...aro.org>,
        Bhupesh Sharma <bhupesh.sharma@...aro.org>
Cc:     coresight@...ts.linaro.org, linux-arm-kernel@...ts.infradead.org,
        mathieu.poirier@...aro.org, mike.leach@...aro.org,
        alexander.shishkin@...ux.intel.com, linux-kernel@...r.kernel.org,
        bhupesh.linux@...il.com,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [PATCH v2] coresight: etm4x: Fix crash observed on Qcom ETM parts
 with 'Low power override'

Hi Bupesh,
\
On 14/09/2022 15:43, Suzuki K Poulose wrote:
> On 13/09/2022 11:52, Leo Yan wrote:
>> Hi Bhupesh,
>>
>> On Thu, Aug 25, 2022 at 10:52:32AM +0530, Bhupesh Sharma wrote:
>>> Some Qualcomm ETM implementations require skipping powering up
>>> the trace unit, as the ETMs are in the same power domain as
>>> their CPU cores.
>>>
>>> Via commit 5214b563588e ("coresight: etm4x: Add support for
>>> sysreg only devices"), the setting of 'skip_power_up' flag was
>>> moved after the 'etm4_init_arch_data' function is called, whereas
>>> the flag value is itself used inside the function. This causes
>>> a crash when ETM mode 'Low-power state behavior override' is set
>>> on some Qualcomm parts.
>>>
>>> Fix the same.
>>>
>>> Fixes: 5214b563588e ("coresight: etm4x: Add support for sysreg only 
>>> devices")
>>> Cc: Mike Leach <mike.leach@...aro.org>
>>> Cc: Suzuki K Poulose <suzuki.poulose@....com>
>>> Cc: Mathieu Poirier <mathieu.poirier@...aro.org>
>>> Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
>>> Signed-off-by: Bhupesh Sharma <bhupesh.sharma@...aro.org>
>>> ---
>>>   - v1 can be seen here: 
>>> https://lore.kernel.org/lkml/20220803191236.3037591-1-bhupesh.sharma@linaro.org/
>>>   - Addressed the review comments from Suzuki.
>>>   - Rebased on linux-next.
>>>
>>>   drivers/hwtracing/coresight/coresight-etm4x-core.c | 13 +++++++++++--
>>>   1 file changed, 11 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/drivers/hwtracing/coresight/coresight-etm4x-core.c 
>>> b/drivers/hwtracing/coresight/coresight-etm4x-core.c
>>> index d39660a3e50c..14c1c7869795 100644
>>> --- a/drivers/hwtracing/coresight/coresight-etm4x-core.c
>>> +++ b/drivers/hwtracing/coresight/coresight-etm4x-core.c
>>> @@ -977,6 +977,16 @@ static bool etm4_init_sysreg_access(struct 
>>> etmv4_drvdata *drvdata,
>>>       if (!cpu_supports_sysreg_trace())
>>>           return false;
>>> +    /*
>>> +     * Some Qualcomm implementations require skipping powering up 
>>> the trace unit,
>>> +     * as the ETMs are in the same power domain as their CPU cores.
>>> +     *
>>> +     * Since the 'skip_power_up' flag is used inside 
>>> 'etm4_init_arch_data' function,
>>> +     * initialize it before the function is called.
>>> +     */
>>> +    if (fwnode_property_present(dev_fwnode(dev), "qcom,skip-power-up"))
>>> +        drvdata->skip_power_up = true;
>>> +
>>
>> I personally think this sentence should be placed in the function
>> etm4_probe(), you need to move it just before smp call
>> etm4_init_arch_data(), this can allow DT property "qcom,skip-power-up"
>> to be respected.
> 
> Or we could move this to init_iomem_access() and explicitly set the flag
> to true in init_sysreg_access().
> 
>>
>>>       /*
>>>        * ETMs implementing sysreg access must implement TRCDEVARCH.
>>>        */
>>> @@ -1951,8 +1961,7 @@ static int etm4_probe(struct device *dev, void 
>>> __iomem *base, u32 etm_pid)
>>>           return -EINVAL;
>>>       /* TRCPDCR is not accessible with system instructions. */
>>> -    if (!desc.access.io_mem ||
>>> -        fwnode_property_present(dev_fwnode(dev), "qcom,skip-power-up"))
>>> +    if (!desc.access.io_mem)
>>>           drvdata->skip_power_up = true;
>>
>> I prefer to move the condition checking for "desc.access.io_mem" to
>> etm4_init_sysreg_access(), this can make sure the flag skip_power_up
>> is set correctly based on property of system register access.
> 
> +1
> 

Do you plan to send an updated patch for this one ?

Kind regards
Suzuki