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

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Message-ID: <0da5622f-35bb-fbe3-37a4-e5c9e825d9ca@arm.com>
Date:   Tue, 11 Oct 2022 16:10:27 +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 11/10/2022 12:10, Mike Leach wrote:
> Hi suzuki,
> 
> On Fri, 7 Oct 2022 at 18:53, Suzuki K Poulose <suzuki.poulose@....com> wrote:
>>
>> 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.
>>
> 
> That also returns -EINVAL, as both call the same underlying allocator.

You're right, the check in coresight_trace_id_map_get_cpu_id(),
confused me.

> However happy to add on the comments for the exported functions

Yes, please.

Thanks Mike

Suzuki