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From:   Amit Kucheria <amit.kucheria@verdurent.com>
Date:   Wed, 16 Oct 2019 22:45:55 +0530
Message-ID: <CAHLCerN0CWOox-_=ywVO40R9LCahBRoU6Myg3Ca3p_TkZyJAMw@mail.gmail.com>
Subject: Re: [PATCH] thermal: create softlink by name for thermal_zone and cooling_device
To:     Wei Wang <wvw@google.com>
Cc:     wei.vince.wang@gmail.com, Zhang Rui <rui.zhang@intel.com>,
        Eduardo Valentin <edubezval@gmail.com>,
        Daniel Lezcano <daniel.lezcano@linaro.org>,
        Linux PM list <linux-pm@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>
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Sender: linux-kernel-owner@vger.kernel.org
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On Wed, Oct 16, 2019 at 10:20 PM Amit Kucheria
<amit.kucheria@verdurent.com> wrote:
>
> On Tue, Oct 15, 2019 at 11:43 AM Wei Wang <wvw@google.com> wrote:
> >
> > The paths thermal_zone%d and cooling_device%d are not intuitive and the
> > numbers are subject to change due to device tree change. This usually
> > leads to tree traversal in userspace code.
> > The patch creates `tz-by-name' and `cdev-by-name' for thermal zone and
> > cooling_device respectively.
>
> I like this.
>
> > Signed-off-by: Wei Wang <wvw@google.com>
> > ---
> >  drivers/thermal/thermal_core.c | 23 +++++++++++++++++++++--
> >  1 file changed, 21 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/thermal/thermal_core.c b/drivers/thermal/thermal_core.c
> > index d4481cc8958f..0ff8fb1d7b0a 100644
> > --- a/drivers/thermal/thermal_core.c
> > +++ b/drivers/thermal/thermal_core.c
> > @@ -22,6 +22,7 @@
> >  #include <net/netlink.h>
> >  #include <net/genetlink.h>
> >  #include <linux/suspend.h>
> > +#include <linux/kobject.h>
> >
> >  #define CREATE_TRACE_POINTS
> >  #include <trace/events/thermal.h>
> > @@ -46,6 +47,8 @@ static DEFINE_MUTEX(poweroff_lock);
> >
> >  static atomic_t in_suspend;
> >  static bool power_off_triggered;
> > +static struct kobject *cdev_link_kobj;
> > +static struct kobject *tz_link_kobj;
> >
> >  static struct thermal_governor *def_governor;
> >
> > @@ -954,7 +957,7 @@ __thermal_cooling_device_register(struct device_node *np,
> >         struct thermal_zone_device *pos = NULL;
> >         int result;
> >
> > -       if (type && strlen(type) >= THERMAL_NAME_LENGTH)
> > +       if (!type || !type[0] || strlen(type) >= THERMAL_NAME_LENGTH)
> >                 return ERR_PTR(-EINVAL);
>
> This should be a separate fix, if needed.
>
> >         if (!ops || !ops->get_max_state || !ops->get_cur_state ||
> > @@ -989,9 +992,15 @@ __thermal_cooling_device_register(struct device_node *np,
> >                 return ERR_PTR(result);
> >         }
> >
> > -       /* Add 'this' new cdev to the global cdev list */
> > +       /* Add 'this' new cdev to the global cdev list and create link*/
> >         mutex_lock(&thermal_list_lock);
> >         list_add(&cdev->node, &thermal_cdev_list);
> > +       if (!cdev_link_kobj)
> > +               cdev_link_kobj = kobject_create_and_add("cdev-by-name",
> > +                                               cdev->device.kobj.parent);
> > +       if (!cdev_link_kobj || sysfs_create_link(cdev_link_kobj,
> > +                                               &cdev->device.kobj, cdev->type))
> > +               dev_err(&cdev->device, "Failed to create cdev-by-name link\n");
>
> Any reason not to use the following form instead? It seems easier to read.
>
> if (!cdev_link_kobj) {
>                cdev_link_kobj = kobject_create_and_add("cdev-by-name",
>                                                cdev->device.kobj.parent);
>               ret = sysfs_create_link(cdev_link_kobj,
>                                               &cdev->device.kobj, cdev->type))
>               if (ret)
>                        dev_err(&cdev->device, "Failed to create
> cdev-by-name link\n");
> }

I can now see why you had to do that - none of the other links would
get created after the first one.

Perhaps create the directories in the __init functions and only create
the links here?


> >         mutex_unlock(&thermal_list_lock);
> >
> >         /* Update binding information for 'this' new cdev */
> > @@ -1157,6 +1166,8 @@ void thermal_cooling_device_unregister(struct thermal_cooling_device *cdev)
> >                         }
> >                 }
> >         }
> > +       if (cdev_link_kobj)
> > +               sysfs_remove_link(cdev_link_kobj, cdev->type);
> >
> >         mutex_unlock(&thermal_list_lock);
> >
> > @@ -1340,6 +1351,12 @@ thermal_zone_device_register(const char *type, int trips, int mask,
> >
> >         mutex_lock(&thermal_list_lock);
> >         list_add_tail(&tz->node, &thermal_tz_list);
> > +       if (!tz_link_kobj)
> > +               tz_link_kobj = kobject_create_and_add("tz-by-name",
> > +                                               tz->device.kobj.parent);
> > +       if (!tz_link_kobj || sysfs_create_link(tz_link_kobj,
> > +                                               &tz->device.kobj, tz->type))
> > +               dev_err(&tz->device, "Failed to create tz-by-name link\n");
>
> Same as above.
>
> >         mutex_unlock(&thermal_list_lock);
> >
> >         /* Bind cooling devices for this zone */
> > @@ -1411,6 +1428,8 @@ void thermal_zone_device_unregister(struct thermal_zone_device *tz)
> >                         }
> >                 }
> >         }
> > +       if (tz_link_kobj)
> > +               sysfs_remove_link(tz_link_kobj, tz->type);
> >
> >         mutex_unlock(&thermal_list_lock);
> >
> > --
> > 2.23.0.700.g56cf767bdb-goog
> >