Re: [PATCH v3 02/11] coresight-tpda: Add DSB dataset support

[Tao Zhang <quic_taozha@quicinc.com>]

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".

> Suzuki
>
>