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

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Date:   Thu, 6 Oct 2022 14:54:50 +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 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>
> > ---
> >   drivers/hwtracing/coresight/coresight-stm.c | 41 +++++++--------------
> >   1 file changed, 14 insertions(+), 27 deletions(-)
> >
> > diff --git a/drivers/hwtracing/coresight/coresight-stm.c b/drivers/hwtracing/coresight/coresight-stm.c
> > index bb14a3a8a921..9ef3e923a930 100644
> > --- a/drivers/hwtracing/coresight/coresight-stm.c
> > +++ b/drivers/hwtracing/coresight/coresight-stm.c
> > @@ -31,6 +31,7 @@
> >   #include <linux/stm.h>
> >
> >   #include "coresight-priv.h"
> > +#include "coresight-trace-id.h"
> >
> >   #define STMDMASTARTR                        0xc04
> >   #define STMDMASTOPR                 0xc08
> > @@ -615,24 +616,7 @@ static ssize_t traceid_show(struct device *dev,
> >       val = drvdata->traceid;
> >       return sprintf(buf, "%#lx\n", val);
> >   }
> > -
> > -static ssize_t traceid_store(struct device *dev,
> > -                          struct device_attribute *attr,
> > -                          const char *buf, size_t size)
> > -{
> > -     int ret;
> > -     unsigned long val;
> > -     struct stm_drvdata *drvdata = dev_get_drvdata(dev->parent);
> > -
> > -     ret = kstrtoul(buf, 16, &val);
> > -     if (ret)
> > -             return ret;
> > -
> > -     /* traceid field is 7bit wide on STM32 */
> > -     drvdata->traceid = val & 0x7f;
> > -     return size;
> > -}
> > -static DEVICE_ATTR_RW(traceid);
> > +static DEVICE_ATTR_RO(traceid);
> >
> >   #define coresight_stm_reg(name, offset)     \
> >       coresight_simple_reg32(struct stm_drvdata, name, offset)
> > @@ -819,14 +803,6 @@ static void stm_init_default_data(struct stm_drvdata *drvdata)
> >        */
> >       drvdata->stmsper = ~0x0;
> >
> > -     /*
> > -      * The trace ID value for *ETM* tracers start at CPU_ID * 2 + 0x10 and
> > -      * anything equal to or higher than 0x70 is reserved.  Since 0x00 is
> > -      * also reserved the STM trace ID needs to be higher than 0x00 and
> > -      * lowner than 0x10.
> > -      */
> > -     drvdata->traceid = 0x1;
> > -
> >       /* Set invariant transaction timing on all channels */
> >       bitmap_clear(drvdata->chs.guaranteed, 0, drvdata->numsp);
> >   }
> > @@ -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.

Mike


> Suzuki



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