Re: [PATCH v4 3/6] coresight: Add generic sysfs link creation functions.

[Mike Leach <mike.leach@linaro.org>]

Hi Mathieu,

On Fri, 14 Feb 2020 at 23:17, Mathieu Poirier
<mathieu.poirier@linaro.org> wrote:
>
> On Tue, Feb 11, 2020 at 10:58:05AM +0000, Mike Leach wrote:
> > To allow the connections between coresight components to be represented
> > in sysfs, generic methods for creating sysfs links between two coresight
> > devices are added.
> >
> > Signed-off-by: Mike Leach <mike.leach@linaro.org>
> > Reviewed-by: Suzuki K Poulose <suzuki.poulose@arm.com>
> > ---
> >  drivers/hwtracing/coresight/Makefile          |   3 +-
> >  drivers/hwtracing/coresight/coresight-priv.h  |   4 +
> >  drivers/hwtracing/coresight/coresight-sysfs.c | 124 ++++++++++++++++++
> >  include/linux/coresight.h                     |  20 +++
> >  4 files changed, 150 insertions(+), 1 deletion(-)
> >  create mode 100644 drivers/hwtracing/coresight/coresight-sysfs.c
> >
> > diff --git a/drivers/hwtracing/coresight/Makefile b/drivers/hwtracing/coresight/Makefile
> > index 0e3e72f0f510..19497d1d92bf 100644
> > --- a/drivers/hwtracing/coresight/Makefile
> > +++ b/drivers/hwtracing/coresight/Makefile
> > @@ -2,7 +2,8 @@
> >  #
> >  # Makefile for CoreSight drivers.
> >  #
> > -obj-$(CONFIG_CORESIGHT) += coresight.o coresight-etm-perf.o coresight-platform.o
> > +obj-$(CONFIG_CORESIGHT) += coresight.o coresight-etm-perf.o \
> > +                        coresight-platform.o coresight-sysfs.o
> >  obj-$(CONFIG_CORESIGHT_LINK_AND_SINK_TMC) += coresight-tmc.o \
> >                                            coresight-tmc-etf.o \
> >                                            coresight-tmc-etr.o
> > diff --git a/drivers/hwtracing/coresight/coresight-priv.h b/drivers/hwtracing/coresight/coresight-priv.h
> > index 1cad642f27aa..a4a658d46045 100644
> > --- a/drivers/hwtracing/coresight/coresight-priv.h
> > +++ b/drivers/hwtracing/coresight/coresight-priv.h
> > @@ -153,6 +153,10 @@ struct coresight_device *coresight_get_sink_by_id(u32 id);
> >  struct list_head *coresight_build_path(struct coresight_device *csdev,
> >                                      struct coresight_device *sink);
> >  void coresight_release_path(struct list_head *path);
> > +int coresight_add_sysfs_link(struct coresight_sysfs_link *info);
> > +void coresight_remove_sysfs_link(struct coresight_sysfs_link *info);
> > +int coresight_create_conns_sysfs_group(struct coresight_device *csdev);
> > +void coresight_remove_conns_sysfs_group(struct coresight_device *csdev);
> >
> >  #ifdef CONFIG_CORESIGHT_SOURCE_ETM3X
> >  extern int etm_readl_cp14(u32 off, unsigned int *val);
> > diff --git a/drivers/hwtracing/coresight/coresight-sysfs.c b/drivers/hwtracing/coresight/coresight-sysfs.c
> > new file mode 100644
> > index 000000000000..17d565941e5e
> > --- /dev/null
> > +++ b/drivers/hwtracing/coresight/coresight-sysfs.c
> > @@ -0,0 +1,124 @@
> > +// SPDX-License-Identifier: GPL-2.0
> > +/*
> > + * Copyright (c) 2019, Linaro Limited, All rights reserved.
> > + * Author: Mike Leach <mike.leach@linaro.org>
> > + */
> > +
> > +#include <linux/device.h>
> > +#include <linux/kernel.h>
> > +
> > +#include "coresight-priv.h"
> > +
> > +/*
> > + * Connections group - links attribute.
> > + * Count of created links between coresight components in the group.
> > + */
> > +static ssize_t nr_links_show(struct device *dev,
> > +                          struct device_attribute *attr,
> > +                          char *buf)
> > +{
> > +     struct coresight_device *csdev = to_coresight_device(dev);
> > +
> > +     return scnprintf(buf, PAGE_SIZE, "%d\n", csdev->nr_links);
> > +}
> > +static DEVICE_ATTR_RO(nr_links);
> > +
> > +static struct attribute *coresight_conns_attrs[] = {
> > +     &dev_attr_nr_links.attr,
> > +     NULL,
> > +};
> > +
> > +static struct attribute_group coresight_conns_group = {
> > +     .attrs = coresight_conns_attrs,
> > +     .name = "connections",
> > +};
> > +
> > +/*
> > + * Create connections group for CoreSight devices.
> > + * This group will then be used to collate the sysfs links between
> > + * devices.
> > + */
> > +int coresight_create_conns_sysfs_group(struct coresight_device *csdev)
> > +{
> > +     int ret = 0;
> > +
> > +     if (!csdev)
> > +             return -EINVAL;
> > +
> > +     ret = sysfs_create_group(&csdev->dev.kobj, &coresight_conns_group);
> > +     if (ret)
> > +             return ret;
> > +
> > +     csdev->has_conns_grp = true;
>
> The only place coresight_create_conns_sysfs_group() is used is in
> coresight_register() where an error is returned to driver probe() functions if
> an error occurs.  Have you found places where csdev->has_conns_grp is needed?
> If not please remove.
>

There is a sequence of calls in coresight_register() which occur after
the coresight_create_conns_sysfs_group() -
any one of which may throw an error resulting in an immediate
coresight_unregister() and hence
coresight_release_platform_data() => coresight_remove_conns_sysfs_group().
There is also an alternate path through coresight_register() which
also results in coresight_release_platform_data() occurring before we
have created the group.
The flag ensures that both paths clean up the sysfs connection data
correctly and safely.

Regards

Mike

> > +     return ret;
> > +}
> > +
> > +void coresight_remove_conns_sysfs_group(struct coresight_device *csdev)
> > +{
> > +     if (!csdev)
> > +             return;
> > +
> > +     if (csdev->has_conns_grp) {
> > +             sysfs_remove_group(&csdev->dev.kobj, &coresight_conns_group);
> > +             csdev->has_conns_grp = false;
> > +     }
> > +}
> > +
> > +int coresight_add_sysfs_link(struct coresight_sysfs_link *info)
> > +{
> > +     int ret = 0;
> > +
> > +     if (!info)
> > +             return -EINVAL;
> > +     if (!info->orig || !info->target ||
> > +         !info->orig_name || !info->target_name)
> > +             return -EINVAL;
> > +     if (!info->orig->has_conns_grp || !info->target->has_conns_grp)
> > +             return -EINVAL;
> > +
> > +     /* first link orig->target */
> > +     ret = sysfs_add_link_to_group(&info->orig->dev.kobj,
> > +                                   coresight_conns_group.name,
> > +                                   &info->target->dev.kobj,
> > +                                   info->orig_name);
> > +     if (ret)
> > +             return ret;
> > +
> > +     /* second link target->orig */
> > +     ret = sysfs_add_link_to_group(&info->target->dev.kobj,
> > +                                   coresight_conns_group.name,
> > +                                   &info->orig->dev.kobj,
> > +                                   info->target_name);
> > +
> > +     /* error in second link - remove first - otherwise inc counts */
> > +     if (ret) {
> > +             sysfs_remove_link_from_group(&info->orig->dev.kobj,
> > +                                          coresight_conns_group.name,
> > +                                          info->orig_name);
> > +     } else {
> > +             info->orig->nr_links++;
> > +             info->target->nr_links++;
> > +     }
> > +
> > +     return ret;
> > +}
> > +
> > +void coresight_remove_sysfs_link(struct coresight_sysfs_link *info)
> > +{
> > +     if (!info)
> > +             return;
> > +     if (!info->orig || !info->target ||
> > +         !info->orig_name || !info->target_name)
> > +             return;
> > +
> > +     sysfs_remove_link_from_group(&info->orig->dev.kobj,
> > +                                  coresight_conns_group.name,
> > +                                  info->orig_name);
> > +
> > +     sysfs_remove_link_from_group(&info->target->dev.kobj,
> > +                                  coresight_conns_group.name,
> > +                                  info->target_name);
> > +
> > +     info->orig->nr_links--;
> > +     info->target->nr_links--;
> > +}
> > diff --git a/include/linux/coresight.h b/include/linux/coresight.h
> > index 193cc9dbf448..a2ec25e02ca9 100644
> > --- a/include/linux/coresight.h
> > +++ b/include/linux/coresight.h
> > @@ -148,6 +148,20 @@ struct coresight_connection {
> >       struct coresight_device *child_dev;
> >  };
> >
> > +/**
> > + * struct coresight_sysfs_link - representation of a connection in sysfs.
> > + * @orig:            Originating (master) coresight device for the link.
> > + * @orig_name:               Name to use for the link orig->target.
> > + * @target:          Target (slave) coresight device for the link.
> > + * @target_name:     Name to use for the link target->orig.
> > + */
> > +struct coresight_sysfs_link {
> > +     struct coresight_device *orig;
> > +     const char *orig_name;
> > +     struct coresight_device *target;
> > +     const char *target_name;
> > +};
> > +
> >  /**
> >   * struct coresight_device - representation of a device as used by the framework
> >   * @pdata:   Platform data with device connections associated to this device.
> > @@ -165,6 +179,9 @@ struct coresight_connection {
> >   * @ea:              Device attribute for sink representation under PMU directory.
> >   * @ect_dev: Associated cross trigger device. Not part of the trace data
> >   *           path or connections.
> > + * @nr_links:   number of sysfs links created to other components from this
> > + *           device. These will appear in the "connections" group.
> > + * @has_conns_grp: Have added a "connections" group for sysfs links.
> >   */
> >  struct coresight_device {
> >       struct coresight_platform_data *pdata;
> > @@ -180,6 +197,9 @@ struct coresight_device {
> >       struct dev_ext_attribute *ea;
> >       /* cross trigger handling */
> >       struct coresight_device *ect_dev;
> > +     /* sysfs links between components */
> > +     int nr_links;
> > +     bool has_conns_grp;
> >  };
>
> With the above:
>
> Reviewed-by: Mathieu Poirier <mathieu.poirier@linaro.org>
>
> >
> >  /*
> > --
> > 2.17.1
> >



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