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References: <20230310160610.742382-1-james.clark@arm.com> <20230310160610.742382-6-james.clark@arm.com>
 <c468a656-036f-df45-0c5e-034a73ed727a@arm.com>
In-Reply-To: <c468a656-036f-df45-0c5e-034a73ed727a@arm.com>
From:   Mike Leach <mike.leach@linaro.org>
Date:   Tue, 21 Mar 2023 17:56:16 +0000
Message-ID: <CAJ9a7Vg1EebruGT0irGE6sgk-Rs39-ptX_N3U=NkG3OsQeuBFQ@mail.gmail.com>
Subject: Re: [PATCH v2 5/9] coresight: Dynamically add connections
To:     Suzuki K Poulose <suzuki.poulose@arm.com>
Cc:     James Clark <james.clark@arm.com>, coresight@lists.linaro.org,
        Mathieu Poirier <mathieu.poirier@linaro.org>,
        Leo Yan <leo.yan@linaro.org>,
        Alexander Shishkin <alexander.shishkin@linux.intel.com>,
        linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org
Content-Type: text/plain; charset="UTF-8"
Precedence: bulk

Hi James

On Thu, 16 Mar 2023 at 17:12, Suzuki K Poulose <suzuki.poulose@arm.com> wrote:
>
> On 10/03/2023 16:06, James Clark wrote:
> > Add a function for adding connections dynamically. This also removes
> > the 1:1 mapping between port number and the index into the connections
> > array. The only place this mapping was used was in the warning for
> > duplicate output ports, which has been replaced by a search. Other
> > uses of the port number already use the port member variable.
> >
> > Being able to dynamically add connections will allow other devices like
> > CTI to re-use the connection mechanism despite not having explicit
> > connections described in the DT.
> >
> > Signed-off-by: James Clark <james.clark@arm.com>
> > ---
> >   .../hwtracing/coresight/coresight-platform.c  | 77 ++++++++++++++-----
> >   include/linux/coresight.h                     |  7 +-
> >   2 files changed, 64 insertions(+), 20 deletions(-)
> >
> > diff --git a/drivers/hwtracing/coresight/coresight-platform.c b/drivers/hwtracing/coresight/coresight-platform.c
> > index c77238cdf448..16553f7dde12 100644
> > --- a/drivers/hwtracing/coresight/coresight-platform.c
> > +++ b/drivers/hwtracing/coresight/coresight-platform.c
> > @@ -27,8 +27,9 @@ static int coresight_alloc_conns(struct device *dev,
> >                                struct coresight_platform_data *pdata)
> >   {
> >       if (pdata->nr_outconns) {
> > -             pdata->out_conns = devm_kcalloc(dev, pdata->nr_outconns,
> > -                                         sizeof(*pdata->out_conns), GFP_KERNEL);
> > +             pdata->out_conns = devm_krealloc_array(
> > +                     dev, pdata->out_conns, pdata->nr_outconns,
>
> super minor nit:
>                 pdata->out_conns = devm_krealloc_array(dev,
>
>
> > +                     sizeof(*pdata->out_conns), GFP_KERNEL | __GFP_ZERO);
> >               if (!pdata->out_conns)
> >                       return -ENOMEM;
> >       }
> > @@ -36,6 +37,48 @@ static int coresight_alloc_conns(struct device *dev,
> >       return 0;
> >   }
> >
> > +/*
> > + * Add a connection in the first free slot, or realloc
> > + * if there is no space. @conn's contents is copied into the new slot.
> > + *
> > + * If the output port is already assigned on this device, return -EINVAL
> > + */
> > +int coresight_add_conn(struct device *dev,
> > +                    struct coresight_platform_data *pdata,
> > +                    const struct coresight_connection *conn)
> > +{
> > +     int ret;
> > +     struct coresight_connection *free_conn = NULL;
> > +     struct coresight_connection *i;
> > +
> > +     /*
> > +      * Search for a free slot, and while looking for one, warn
> > +      * on any existing duplicate output port.
> > +      */
> > +     for (i = pdata->out_conns; i < pdata->out_conns + pdata->nr_outconns;
> > +          ++i) {
>
> minor nit: I see why you have gone against using "i" as index into
> the array. But I think having that as the index is still better
> readable.
>
>         for (i = 0; i < pdata->nr_outconns; i++) {
>                 struct coresight_connection *c = &pdata->out_conns[i];
>
> > +             if (i->remote_fwnode && conn->port != -1 &&
> > +                 i->port == conn->port) {
> > +                     dev_warn(dev, "Duplicate output port %d\n", i->port);
> > +                     return -EINVAL;
> > +             }

This code assumes that slots are filled sequentially and that it is
not possible to release slots out of order - i.e. if we find a free
slot, there is not a match in a later slot.
I can't think how this could happen but a comment to confirm this
might be needed here.

When we had 1:1 port / array index then this check was guaranteed

Mike


> > +             if (!i->remote_fwnode && !free_conn)
> > +                     free_conn = i;
> > +     }
> > +
> > +     if (!free_conn) {
>
> and:
>         /* No free slots */
>         if (i == pdata->nr_outconns) {
>
> > +             pdata->nr_outconns++;
> > +             ret = coresight_alloc_conns(dev, pdata);
> > +             if (ret)
> > +                     return ret;
> > +             free_conn = &pdata->out_conns[pdata->nr_outconns - 1];
> > +     }
> > +
>
> and:
>         pdata->out_conns[i] = *conn;
>
>
> Otherwise looks good to me.
>
> Suzuki
>
>


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