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

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Message-ID: <CAJ9a7VgrJ3L6o9e0600G_JL6S_PXLsZcQDLPR_YGpSu4L=pOMg@mail.gmail.com>
Date:   Tue, 11 Oct 2022 12:10:53 +0100
From:   Mike Leach <mike.leach@...aro.org>
To:     Suzuki K Poulose <suzuki.poulose@....com>
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

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.

However happy to add on the comments for the exported functions

Regards

Mike
> 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
>


-- 
Mike Leach
Principal Engineer, ARM Ltd.
Manchester Design Centre. UK