Date:   Sat, 25 Mar 2023 19:31:15 +0000
From:   Suzuki K Poulose <suzuki.poulose@....com>
To:     Tao Zhang <quic_taozha@...cinc.com>,
        Mathieu Poirier <mathieu.poirier@...aro.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Konrad Dybcio <konradybcio@...il.com>,
        Mike Leach <mike.leach@...aro.org>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        James Clark <james.clark@....com>
Cc:     Jinlong Mao <quic_jinlmao@...cinc.com>,
        Leo Yan <leo.yan@...aro.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        coresight@...ts.linaro.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org, devicetree@...r.kernel.org,
        Tingwei Zhang <quic_tingweiz@...cinc.com>,
        Yuanfang Zhang <quic_yuanfang@...cinc.com>,
        Trilok Soni <quic_tsoni@...cinc.com>,
        Hao Zhang <quic_hazha@...cinc.com>,
        linux-arm-msm@...r.kernel.org,
        Bjorn Andersson <andersson@...nel.org>
Subject: Re: [PATCH v3 02/11] coresight-tpda: Add DSB dataset support

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@...cinc.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
Suzuki

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