linux-kernel - Re: [PATCH v1] coresight: tpda: fix the logic to setup the element size

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Message-ID: <a2e3bcf2-80c9-4c8b-ad88-bd91c33137b5@oss.qualcomm.com>
Date: Thu, 4 Sep 2025 16:59:11 +0800
From: Jie Gan <jie.gan@....qualcomm.com>
To: Suzuki K Poulose <suzuki.poulose@....com>,
        Jie Gan <jie.gan@....qualcomm.com>, Mike Leach <mike.leach@...aro.org>,
        James Clark <james.clark@...aro.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Tao Zhang <quic_taozha@...cinc.com>,
        Mao Jinlong <quic_jinlmao@...cinc.com>
Cc: tingwei.zhang@....qualcomm.com, coresight@...ts.linaro.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-arm-msm@...r.kernel.org
Subject: Re: [PATCH v1] coresight: tpda: fix the logic to setup the element
 size



On 9/4/2025 4:50 PM, Suzuki K Poulose wrote:
> On 04/09/2025 02:12, Jie Gan wrote:
>>
>>
>> On 9/3/2025 5:45 PM, Jie Gan wrote:
>>>
>>>
>>> On 9/3/2025 4:57 PM, Suzuki K Poulose wrote:
>>>> On 06/08/2025 09:09, Jie Gan wrote:
>>>>> Some TPDM devices support both CMB and DSB datasets, requiring
>>>>> the system to enable the port with both corresponding element sizes.
>>>>>
>>>>> Currently, the logic treats tpdm_read_element_size as successful if
>>>>> the CMB element size is retrieved correctly, regardless of whether
>>>>> the DSB element size is obtained. This behavior causes issues
>>>>> when parsing data from TPDM devices that depend on both element sizes.
>>>>>
>>>>> To address this, the function should explicitly fail if the DSB
>>>>> element size cannot be read correctly.
>>>>
>>>> But what is the device only has CMB ? Back when this was originally 
>>>
>>> We have CMB TPDM, DSB TPDM and CMB&&DSB TPDM.
>>>
>>>> merged, we raised this question and the answer was, "Only one is 
>>>> supported, not both." But this sounds like that is wrong.
>>>
>>> I think we may not answer the previous question clearly. But it 
>>> definitely has issue here.
>>>
>>>> Could we defer the "Warning" to the caller. i.e., Let the caller
>>>> figure out the if the DSB size is found and predicate that on the
>>>> DSB support on the TPDM.
>>>
>>> Understood, below codes will be added in the caller to check the error:
>>> if ((tpdm_data->dsb && !drvdata->dsb_esize) ||
>>>      (tpdm_data->cmb && !drvdata->cmb_esize))
>>>      goto err;
>>>
>>> Thanks,
>>> Jie
>>>
>>
>> Hi Suzuki,
>>
>> I've reviewed the logic here. It's not feasible for the caller to 
>> perform the check, since we first retrieve TPDM's drvdata, which adds 
>> complexity to the code. I believe it's better to handle this within 
>> the function itself.
>>
>> We are expecting the element_size for cmb if the condition is true, as 
>> well as dsb:
>> if (tpdm_data->dsb)
>> ...
>> should obtain a valid element size for dsb.
>> ...
>>
>> if (tpdm_data->cmb)
>> ...
>> should obtain a valid element size for cmb.
>> ...
>>
> 
> Ok, fair enough. Please resend the patch without the dependency on the 
> static TPDM patch. Given this is a fix, this could go in without waiting 
> for the new series.
> 

Hi Suzuki,

This patch has not dependency with the static TPDM patch series.

Actually, the static TPDM patch series depends on this fix patch because 
both modified same code snippet in function tpdm_read_element_size.

Thanks,
Jie

> Suzuki
> 
> 
> 
>> Thanks,
>> Jie
>>
>>>>
>>>> Suzuki
>>>>
>>>>>
>>>>> Fixes: e6d7f5252f73 ("coresight-tpda: Add support to configure CMB 
>>>>> element")
>>>>> Signed-off-by: Jie Gan <jie.gan@....qualcomm.com>
>>>>> ---
>>>>>   drivers/hwtracing/coresight/coresight-tpda.c | 3 +++
>>>>>   1 file changed, 3 insertions(+)
>>>>>
>>>>> diff --git a/drivers/hwtracing/coresight/coresight-tpda.c b/ 
>>>>> drivers/ hwtracing/coresight/coresight-tpda.c
>>>>> index 0633f04beb24..333b3cb23685 100644
>>>>> --- a/drivers/hwtracing/coresight/coresight-tpda.c
>>>>> +++ b/drivers/hwtracing/coresight/coresight-tpda.c
>>>>> @@ -71,6 +71,8 @@ static int tpdm_read_element_size(struct 
>>>>> tpda_drvdata *drvdata,
>>>>>       if (tpdm_data->dsb) {
>>>>>           rc = fwnode_property_read_u32(dev_fwnode(csdev->dev.parent),
>>>>>                   "qcom,dsb-element-bits", &drvdata->dsb_esize);
>>>>> +        if (rc)
>>>>> +            goto out;
>>>>>       }
>>>>>       if (tpdm_data->cmb) {
>>>>> @@ -78,6 +80,7 @@ static int tpdm_read_element_size(struct 
>>>>> tpda_drvdata *drvdata,
>>>>>                   "qcom,cmb-element-bits", &drvdata->cmb_esize);
>>>>>       }
>>>>> +out:
>>>>>       if (rc)
>>>>>           dev_warn_once(&csdev->dev,
>>>>>               "Failed to read TPDM Element size: %d\n", rc);
>>>>
>>>>
>>>
>>
> 
>