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Date:   Thu, 30 Mar 2023 22:07:07 +0800
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Subject: Re: [PATCH v3 02/11] coresight-tpda: Add DSB dataset support
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To:     Suzuki K Poulose <suzuki.poulose@arm.com>,
        Mathieu Poirier <mathieu.poirier@linaro.org>,
        Alexander Shishkin <alexander.shishkin@linux.intel.com>,
        Konrad Dybcio <konradybcio@gmail.com>,
        Mike Leach <mike.leach@linaro.org>,
        Rob Herring <robh+dt@kernel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
        James Clark <james.clark@arm.com>
CC:     Jinlong Mao <quic_jinlmao@quicinc.com>,
        Leo Yan <leo.yan@linaro.org>,
        "Greg Kroah-Hartman" <gregkh@linuxfoundation.org>,
        <coresight@lists.linaro.org>,
        <linux-arm-kernel@lists.infradead.org>,
        <linux-kernel@vger.kernel.org>, <devicetree@vger.kernel.org>,
        Tingwei Zhang <quic_tingweiz@quicinc.com>,
        Yuanfang Zhang <quic_yuanfang@quicinc.com>,
        Trilok Soni <quic_tsoni@quicinc.com>,
        Hao Zhang <quic_hazha@quicinc.com>,
        <linux-arm-msm@vger.kernel.org>,
        Bjorn Andersson <andersson@kernel.org>
References: <1679551448-19160-1-git-send-email-quic_taozha@quicinc.com>
 <1679551448-19160-3-git-send-email-quic_taozha@quicinc.com>
 <e578790c-4794-5609-16e8-15d63082760e@arm.com>
 <51ad3cb3-bd83-51c9-52bc-f700cd17103c@quicinc.com>
 <48f31b84-573f-fe1d-bcd7-e55ec7f47831@arm.com>
 <595568c3-d2bc-e37e-83b3-2adfd3fa4193@quicinc.com>
 <6f8b087d-77a7-512e-6504-e4841447eda9@arm.com>
 <edbd1f10-70e5-1fd4-44de-da59b387e9dd@quicinc.com>
 <c3f5af31-b6ef-dc45-25f0-4e52d93fcaa7@arm.com>
From:   Tao Zhang <quic_taozha@quicinc.com>
In-Reply-To: <c3f5af31-b6ef-dc45-25f0-4e52d93fcaa7@arm.com>
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Hi Suzuki,

On 3/28/2023 8:33 PM, Suzuki K Poulose wrote:
> On 28/03/2023 12:31, Tao Zhang wrote:
>> Hi Suzuki,
>>
>> On 3/27/2023 5:43 PM, Suzuki K Poulose wrote:
>>> On 27/03/2023 04:31, Tao Zhang wrote:
>>>>
>>>> On 3/26/2023 3:31 AM, Suzuki K Poulose wrote:
>>>>> On 24/03/2023 14:58, Tao Zhang wrote:
>>>>>> Hi Suzuki,
>>>>>>
>>>>>> 在 3/23/2023 7:51 PM, Suzuki K Poulose 写道:
>>>>>>> On 23/03/2023 06:03, Tao Zhang wrote:
>>>>>>>> Read the DSB element size from the device tree. Set the register
>>>>>>>> bit that controls the DSB element size of the corresponding port.
>>>>>>>>
>>>>>>>> Signed-off-by: Tao Zhang <quic_taozha@quicinc.com>
>>>>>>>> ---
>>>>>>>>   drivers/hwtracing/coresight/coresight-tpda.c | 58 
>>>>>>>> ++++++++++++++++++++++++++++
>>>>>>>>   drivers/hwtracing/coresight/coresight-tpda.h |  4 ++
>>>>>>>>   2 files changed, 62 insertions(+)
>>>>>>>>
>>>>>>>> diff --git a/drivers/hwtracing/coresight/coresight-tpda.c 
>>>>>>>> b/drivers/hwtracing/coresight/coresight-tpda.c
>>>>>>>> index f712e11..8dcfc4a 100644
>>>>>>>> --- a/drivers/hwtracing/coresight/coresight-tpda.c
>>>>>>>> +++ b/drivers/hwtracing/coresight/coresight-tpda.c
>>>>>>>> @@ -21,6 +21,47 @@
>>>>>>>>     DEFINE_CORESIGHT_DEVLIST(tpda_devs, "tpda");
>>>>>>>>   +/* Search and read element data size from the TPDM node in
>>>>>>>> + * the devicetree. Each input port of TPDA is connected to
>>>>>>>> + * a TPDM. Different TPDM supports different types of dataset,
>>>>>>>> + * and some may support more than one type of dataset.
>>>>>>>> + * Parameter "inport" is used to pass in the input port number
>>>>>>>> + * of TPDA, and it is set to 0 in the recursize call.
>>>>>>>> + * Parameter "parent" is used to pass in the original call.
>>>>>>>> + */
>>>>>>>
>>>>>>> I am still not clear why we need to do this recursively ?
>>>>>>
>>>>>> Some TPDMs are not directly output connected to the TPDAs. So here I
>>>>>>
>>>>>> use a recursive method to check from the TPDA input port until I 
>>>>>> find
>>>>>>
>>>>>> the connected TPDM.
>>>>>>
>>>>>> Do you have a better suggestion besides a recursive method?
>>>>>>
>>>>>>>
>>>>>>>> +static int tpda_set_element_size(struct tpda_drvdata *drvdata,
>>>>>>>> +               struct coresight_device *csdev, int inport, 
>>>>>>>> bool parent)
>>>>>>>
>>>>>>> Please could we renamse csdev => tpda_dev
>>>>>>
>>>>>> Since this is a recursively called function, this Coresight 
>>>>>> device is not
>>>>>>
>>>>>> necessarily TPDA, it can be other Coresight device.
>>>>>>
>>>>>>>
>>>>>>>> +{
>>>>>>>> +    static int nr_inport;
>>>>>>>> +    int i;
>>>>>>>> +    struct coresight_device *in_csdev;
>>>>>>>
>>>>>>> similarly tpdm_dev ?
>>>>>> Same as above, this variable may not necessarily be a TPDM.
>>>>>>>
>>>>>>> Could we not add a check here to see if the dsb_esize[inport] is 
>>>>>>> already
>>>>>>> set and then bail out, reading this over and over ?
>>>>>>>
>>>>>> I will update this in the next patch series.
>>>>>>>> +
>>>>>>>> +    if (inport > (TPDA_MAX_INPORTS - 1))
>>>>>>>> +        return -EINVAL;
>>>>>>>> +
>>>>>>>> +    if (parent)
>>>>>>>> +        nr_inport = inport;
>>>>>>>> +
>>>>>>>> +    for (i = 0; i < csdev->pdata->nr_inconns; i++) {
>>>>>>>> +        in_csdev = csdev->pdata->in_conns[i].remote_dev;
>>>>>>>
>>>>>>> Please note, the names of the structure field might change in the
>>>>>>> next version of James' series
>>>>>> Got it. I will keep an eye out for the James' patch series.
>>>>>>>
>>>>>>>> +        if (!in_csdev)
>>>>>>>> +            break;
>>>>>>>> +
>>>>>>>> +        if (parent)
>>>>>>>> +            if (csdev->pdata->in_conns[i].port != inport)
>>>>>>>> +                continue;
>>>>>>>> +
>>>>>>>> +        if (in_csdev && strstr(dev_name(&in_csdev->dev), 
>>>>>>>> "tpdm")) {
>>>>>>>
>>>>>>> Isn't there a better way to distinguish a device to be TPDM ? 
>>>>>>> May be we
>>>>>>> could even add a source_sub_type - SOURCE_TPDM instead of using
>>>>>>> SOURCE_OTHERS ? Do you expect other sources to be connected to 
>>>>>>> TPDA?
>>>>>>> e.g., STMs ?
>>>>>>
>>>>>> I can add "SOURCE_TPDM" as a source_sub_type, but SOURCE_OTHERS 
>>>>>> needs
>>>>>>
>>>>>> to be kept since the other Coresight component we will upstream 
>>>>>> later may
>>>>>>
>>>>>> need it.
>>>>>>
>>>>>>>
>>>>>>>> + of_property_read_u32(in_csdev->dev.parent->of_node,
>>>>>>>> +                    "qcom,dsb-element-size", 
>>>>>>>> &drvdata->dsb_esize[nr_inport]);
>>>>>>>> +            break;
>>>>>>>> +        }
>>>>>>>> +        tpda_set_element_size(drvdata, in_csdev, 0, false);
>>>>>>>
>>>>>>> What is the point of this ? Is this for covering the a TPDA 
>>>>>>> connected to
>>>>>>> another TPDA ?
>>>>>>>
>>>>>>> e.g., { TPDM0, TPDM1 } -> TPDA0 -> TPDA1 ?
>>>>>>
>>>>>> A TPDM may not connect to the TPDA directly, for example,
>>>>>>
>>>>>> TPDM0 ->FUNNEL0->FUNNEL1->TPDA0
>>>>>>
>>>>>> And many TPDMs can connect to one TPDA, one input port on TPDA 
>>>>>> only has
>>>>>>
>>>>>> one TPDM connected. Therefore, we use a recursive method to find 
>>>>>> the TPDM
>>>>>>
>>>>>> corresponding to the input port of TPDA.
>>>>>
>>>>> How do you find out decide what to choose, if there are multiple 
>>>>> TPDMs
>>>>> connected to FUNNEL0 or even FUNNEL1 ?
>>>>>
>>>>> e.g
>>>>>
>>>>> TPDM0->FUNNEL0->FUNNEL1->TPDA0
>>>>>                 /
>>>>>           TPDM1
>>>>
>>>> We can find out the corresponding TPDM by the input port number of 
>>>> TPDA.
>>>>
>>>> Each input port is connected to a TPDM. So we have an input port 
>>>> number in
>>>>
>>>> the input parameter of the recursive lookup function 
>>>> "tpda_set_element_size".
>>>
>>> I don't understand, how you would figure out, in the above situation.
>>> i.e., FUNNEL1 is connected to TPDA0, but there are two TPDMs that could
>>> be pumping the trace. They both arrive via FUNNEL1. So, how does that
>>> solve your problem ?
>>
>> In our HW design, the input ports of TPDA and TPDM are one-one-one 
>> corresponding.  Only one
>>
>> TPDM can be found connected from one TPDA's input port. The path to a 
>> TPDA input port doesn't
>>
>> connect more than one TPDM. It's by HW design.
>
> Your current designs may be like that. But as far as the driver is
> concerned, I would like to add in extra measures to ensure that it
> encounters a variation from the above on a future platform. So, please
> could you add a check to detect this case and add a WARNING ?

Got it, I will update it according to your advice in the next patch series.


Tao

>
> Suzuki
>
>
>>
>>
>> Tao
>>
>>>
>>> Suzuki
>>>
>>>
>>>>
>>>>> Suzuki
>>>>>
>>>>>
>>>
>