Re: [PATCH v5 07/14] coresight: cti: Add device tree support for custom CTI.

Mathieu Poirier
2019-11-29T21:11:32Z

On Fri, 29 Nov 2019 at 07:16, Suzuki Kuruppassery Poulose
<suzuki.poulose@arm.com> wrote:
>
> On 25/11/2019 21:22, Mathieu Poirier wrote:
> > On Tue, Nov 19, 2019 at 11:19:05PM +0000, Mike Leach wrote:
> >> Adds support for CTIs whose connections are implementation defined at
> >> hardware design time, and not constrained by v8 architecture.
> >>
> >> These CTIs have no standard connection setup, all the settings have to
> >> be defined in the device tree files. The patch creates a set of connections
> >> and trigger signals based on the information provided.
> >>
> >> Signed-off-by: Mike Leach <mike.leach@linaro.org>
> >> ---
> >> .../coresight/coresight-cti-platform.c | 250 +++++++++++++++++-
> >> .../hwtracing/coresight/coresight-cti-sysfs.c | 11 +
> >> 2 files changed, 257 insertions(+), 4 deletions(-)
>
> >> +static int cti_plat_create_impdef_connections(struct device *dev,
> >> + struct cti_drvdata *drvdata)
> >> +{
> >> + int rc = 0;
> >> + struct fwnode_handle *fwnode = dev_fwnode(dev);
> >> + struct fwnode_handle *child = NULL;
> >> +
> >> + if (IS_ERR_OR_NULL(fwnode))
> >> + return -EINVAL;
> >> +
> >> + fwnode_for_each_child_node(fwnode, child) {
> >> + if (cti_plat_node_name_eq(child, CTI_DT_CONNS))
> >> + rc = cti_plat_create_connection(dev, drvdata, child);
> >> + if (rc != 0)
> >> + break;
> >> + }
> >> + fwnode_handle_put(child);
> >
> > As far as I can tell we don't need to call fwnode_handle_put()?
>
> Actually we do, if we break the scan in between, at least for of_nodes.
> I had to literally look it down all the way down to confirm this.
>
> So for CONFIG_OF it ends up in of_get_next_available_child(), which
> drops the ref on "prev" and grabs the "next". So in case we break
> the loop, we must drop the ref on the child.

Well spotted.

> Otherwise, the last
> result would be NULL, which would have dropped the ref on the "last"
> valid entry. And this is harmless with a NULL ptr.
>
> Suzuki