Re: [PATCH v3 06/13] coresight: Fix loss of connection info when a module is unloaded

[Suzuki K Poulose]

On 30/03/2023 13:42, Suzuki K Poulose wrote:
> Hi James
>
> On 29/03/2023 12:53, James Clark wrote:
> > child_fwnode should be a read only property based on the DT. If it's
> > cleared on the parent device when a child is unloaded, then when the
> > child is loaded again the connection won't be remade.
> >
> > child_dev should be cleared instead which signifies that the connection
> > should be remade when the child_fwnode registers a new coresight_device.
> >
> > Similarly the reference count shouldn't be decremented as long as the
> > parent device exists. The correct place to drop the reference is in
> > coresight_release_platform_data() which is already done.
> >
> > Signed-off-by: James Clark <james.clark@xxxxxxx>
>
> This looks like a bug in the existing driver. Please could you keep this
> at the beginning of the series, so that it is easier to backport for
> stable ?
>
> Also, please add :
>
> Fixes: 37ea1ffddffa ("coresight: Use fwnode handle instead of device 
> names")
> Fixes: 2af89ebacf29 ("coresight: Clear the connection field properly")
>
>
> > ---
> >   drivers/hwtracing/coresight/coresight-core.c | 10 ++--------
> >   1 file changed, 2 insertions(+), 8 deletions(-)
> >
> > diff --git a/drivers/hwtracing/coresight/coresight-core.c 
> > b/drivers/hwtracing/coresight/coresight-core.c
> > index bfe1b93aca4e..12cbb68e8e1c 100644
> > --- a/drivers/hwtracing/coresight/coresight-core.c
> > +++ b/drivers/hwtracing/coresight/coresight-core.c
> > @@ -1414,13 +1414,8 @@ static int coresight_remove_match(struct device 
> > *dev, void *data)
> >           if (csdev->dev.fwnode == conn->dest_fwnode) {
> >               iterator->orphan = true;
> >               coresight_remove_links(iterator, conn);
> > -            /*
> > -             * Drop the reference to the handle for the remote
> > -             * device acquired in parsing the connections from
> > -             * platform data.
> > -             */
> > -            fwnode_handle_put(conn->dest_fwnode);
> > -            conn->dest_fwnode = NULL;
> > +
> > +            conn->dest_dev = NULL;
> >               /* No need to continue */
> >               break;
> >           }
> > @@ -1553,7 +1548,6 @@ void coresight_release_platform_data(struct 
> > coresight_device *csdev,
> >            * is going away
> >            */
> >           fwnode_handle_put(conns[i].dest_fwnode);
> > -        pdata->out_conns[i].dest_fwnode = NULL;
>
> This change is not required, as we are freeing the pdata anyway.
> Keeping this might be beneficial if someone else comes looking
> for references while we are going out. I don't see how we could
> hit that, but just to be safe.

For reference, I could reproduce the problem by :

On juno, load all coresight modules.

$ cd /sys/bus/coresight/devices/
$ echo 1 > tmc_etr0/enable_sink
$ echo 1 > etm0/enable_source

Works fine ^

$ echo 0 > etm0/enable_source
$ rmmod coresight-funnel
$ modprobe coresight-funnel
$ echo 1 > etm0/enable_source
-bash: echo: write error: Invalid argument

Suzuki

> Suzuki