linux-kernel - Re: [PATCH v3 03/13] coresight: stm: Update STM driver to use Trace ID API

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Message-ID: <55170f1f-99f7-6e25-55d3-5d7247737afc@arm.com>
Date:   Fri, 7 Oct 2022 18:53:03 +0100
From:   Suzuki K Poulose <suzuki.poulose@....com>
To:     Mike Leach <mike.leach@...aro.org>
Cc:     coresight@...ts.linaro.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org, mathieu.poirier@...aro.org,
        peterz@...radead.org, mingo@...hat.com, acme@...nel.org,
        linux-perf-users@...r.kernel.org, leo.yan@...aro.org,
        quic_jinlmao@...cinc.com
Subject: Re: [PATCH v3 03/13] coresight: stm: Update STM driver to use Trace
 ID API

On 06/10/2022 14:54, Mike Leach wrote:
> Hi Suzuki,
> 
> On Mon, 3 Oct 2022 at 10:04, Suzuki K Poulose <suzuki.poulose@....com> wrote:
>>
>> On 09/08/2022 23:33, Mike Leach wrote:
>>> Updates the STM driver to use the trace ID allocation API.
>>> This uses the _system_id calls to allocate an ID on device poll,
>>> and release on device remove.
>>>
>>> The sysfs access to the STMTRACEIDR register has been changed from RW
>>> to RO. Having this value as writable is not appropriate for the new
>>> Trace ID scheme - and had potential to cause errors in the previous
>>> scheme if values clashed with other sources.
>>>
>>> Signed-off-by: Mike Leach <mike.leach@...aro.org>
>>> Reviewed-by: Suzuki K Poulose <suzuki.poulose@....com>

>>> @@ -854,7 +830,7 @@ static void stm_init_generic_data(struct stm_drvdata *drvdata,
>>>
>>>    static int stm_probe(struct amba_device *adev, const struct amba_id *id)
>>>    {
>>> -     int ret;
>>> +     int ret, trace_id;
>>>        void __iomem *base;
>>>        struct device *dev = &adev->dev;
>>>        struct coresight_platform_data *pdata = NULL;
>>> @@ -938,12 +914,22 @@ static int stm_probe(struct amba_device *adev, const struct amba_id *id)
>>>                goto stm_unregister;
>>>        }
>>>
>>> +     trace_id = coresight_trace_id_get_system_id();
>>> +     if (trace_id < 0) {
>>
>> The above API returns "INVALID_ID" and not a negative error status.
>> I think it is better to fix the API to return:
>>
>>     ret < 0  - If there is any error
>>              - Otherwise a positive integer
>> And the users should be kept unaware of which ID is valid or invalid.
>>
> 
> coresight_trace_id_get_system_id() returns the ID if one can be
> allocated or -EINVAL if not.
> 
> Not sure what you are looking at here.

Sorry, indeed I was mistaken there. It is the get_cpu_id() which
returns the INVALID_ID on failure. Please could we make that
consistent with this scheme ? i.e, < 0 on error.

Also, please could we add a comment above the exported functions
on their entry/exit criteria ? It is not clearly evident, unless
we follow the code and figure out.

Cheers
Suzuki