Re: [PATCH v2 09/15] peci: Add sysfs interface for PECI bus

["Winiarska, Iwona" <iwona.winiarska@intel.com>]

On Fri, 2021-08-27 at 12:11 -0700, Dan Williams wrote:
> On Tue, Aug 3, 2021 at 4:35 AM Iwona Winiarska
> <iwona.winiarska@intel.com> wrote:
> > 
> > PECI devices may not be discoverable at the time when PECI controller is
> > being added (e.g. BMC can boot up when the Host system is still in S5).
> > Since we currently don't have the capabilities to figure out the Host
> > system state inside the PECI subsystem itself, we have to rely on
> > userspace to do it for us.
> > 
> > In the future, PECI subsystem may be expanded with mechanisms that allow
> > us to avoid depending on userspace interaction (e.g. CPU presence could
> > be detected using GPIO, and the information on whether it's discoverable
> > could be obtained over IPMI).
> 
> Thanks for this detail.
> 
> > Unfortunately, those methods may ultimately not be available (support
> > will vary from platform to platform), which means that we still need
> > platform independent method triggered by userspace.
> > 
> > Signed-off-by: Iwona Winiarska <iwona.winiarska@intel.com>
> > ---
> >  Documentation/ABI/testing/sysfs-bus-peci | 16 +++++
> >  drivers/peci/Makefile                    |  2 +-
> >  drivers/peci/core.c                      |  3 +-
> >  drivers/peci/device.c                    |  1 +
> >  drivers/peci/internal.h                  |  5 ++
> >  drivers/peci/sysfs.c                     | 82 ++++++++++++++++++++++++
> >  6 files changed, 107 insertions(+), 2 deletions(-)
> >  create mode 100644 Documentation/ABI/testing/sysfs-bus-peci
> >  create mode 100644 drivers/peci/sysfs.c
> > 
> > diff --git a/Documentation/ABI/testing/sysfs-bus-peci
> > b/Documentation/ABI/testing/sysfs-bus-peci
> > new file mode 100644
> > index 000000000000..56c2b2216bbd
> > --- /dev/null
> > +++ b/Documentation/ABI/testing/sysfs-bus-peci
> > @@ -0,0 +1,16 @@
> > +What:          /sys/bus/peci/rescan
> > +Date:          July 2021
> > +KernelVersion: 5.15
> > +Contact:       Iwona Winiarska <iwona.winiarska@intel.com>
> > +Description:
> > +               Writing a non-zero value to this attribute will
> > +               initiate scan for PECI devices on all PECI controllers
> > +               in the system.
> > +
> > +What:          /sys/bus/peci/devices/<controller_id>-<device_addr>/remove
> > +Date:          July 2021
> > +KernelVersion: 5.15
> > +Contact:       Iwona Winiarska <iwona.winiarska@intel.com>
> > +Description:
> > +               Writing a non-zero value to this attribute will
> > +               remove the PECI device and any of its children.
> > diff --git a/drivers/peci/Makefile b/drivers/peci/Makefile
> > index c5f9d3fe21bb..917f689e147a 100644
> > --- a/drivers/peci/Makefile
> > +++ b/drivers/peci/Makefile
> > @@ -1,7 +1,7 @@
> >  # SPDX-License-Identifier: GPL-2.0-only
> > 
> >  # Core functionality
> > -peci-y := core.o request.o device.o
> > +peci-y := core.o request.o device.o sysfs.o
> >  obj-$(CONFIG_PECI) += peci.o
> > 
> >  # Hardware specific bus drivers
> > diff --git a/drivers/peci/core.c b/drivers/peci/core.c
> > index d143f1a7fe98..c473acb3c2a0 100644
> > --- a/drivers/peci/core.c
> > +++ b/drivers/peci/core.c
> > @@ -34,7 +34,7 @@ struct device_type peci_controller_type = {
> >         .release        = peci_controller_dev_release,
> >  };
> > 
> > -static int peci_controller_scan_devices(struct peci_controller *controller)
> > +int peci_controller_scan_devices(struct peci_controller *controller)
> >  {
> >         int ret;
> >         u8 addr;
> > @@ -159,6 +159,7 @@ EXPORT_SYMBOL_NS_GPL(devm_peci_controller_add, PECI);
> > 
> >  struct bus_type peci_bus_type = {
> >         .name           = "peci",
> > +       .bus_groups     = peci_bus_groups,
> >  };
> > 
> >  static int __init peci_init(void)
> > diff --git a/drivers/peci/device.c b/drivers/peci/device.c
> > index 32811248997b..d77d9dabd51e 100644
> > --- a/drivers/peci/device.c
> > +++ b/drivers/peci/device.c
> > @@ -110,5 +110,6 @@ static void peci_device_release(struct device *dev)
> >  }
> > 
> >  struct device_type peci_device_type = {
> > +       .groups         = peci_device_groups,
> >         .release        = peci_device_release,
> >  };
> > diff --git a/drivers/peci/internal.h b/drivers/peci/internal.h
> > index 57d11a902c5d..978e12c8e1d3 100644
> > --- a/drivers/peci/internal.h
> > +++ b/drivers/peci/internal.h
> > @@ -8,6 +8,7 @@
> >  #include <linux/types.h>
> > 
> >  struct peci_controller;
> > +struct attribute_group;
> >  struct peci_device;
> >  struct peci_request;
> > 
> > @@ -19,12 +20,16 @@ struct peci_request *peci_request_alloc(struct
> > peci_device *device, u8 tx_len, u
> >  void peci_request_free(struct peci_request *req);
> > 
> >  extern struct device_type peci_device_type;
> > +extern const struct attribute_group *peci_device_groups[];
> > 
> >  int peci_device_create(struct peci_controller *controller, u8 addr);
> >  void peci_device_destroy(struct peci_device *device);
> > 
> >  extern struct bus_type peci_bus_type;
> > +extern const struct attribute_group *peci_bus_groups[];
> 
> To me, sysfs.c is small enough to just fold into core.c, then no need
> to declare public attribute arrays like this, but up to you if you
> prefer the sysfs.c split.

Left the sysfs split for now.

> 
> > 
> >  extern struct device_type peci_controller_type;
> > 
> > +int peci_controller_scan_devices(struct peci_controller *controller);
> > +
> >  #endif /* __PECI_INTERNAL_H */
> > diff --git a/drivers/peci/sysfs.c b/drivers/peci/sysfs.c
> > new file mode 100644
> > index 000000000000..db9ef05776e3
> > --- /dev/null
> > +++ b/drivers/peci/sysfs.c
> > @@ -0,0 +1,82 @@
> > +// SPDX-License-Identifier: GPL-2.0-only
> > +// Copyright (c) 2021 Intel Corporation
> > +
> > +#include <linux/device.h>
> > +#include <linux/kernel.h>
> > +#include <linux/peci.h>
> > +
> > +#include "internal.h"
> > +
> > +static int rescan_controller(struct device *dev, void *data)
> > +{
> > +       if (dev->type != &peci_controller_type)
> > +               return 0;
> > +
> > +       return peci_controller_scan_devices(to_peci_controller(dev));
> > +}
> > +
> > +static ssize_t rescan_store(struct bus_type *bus, const char *buf, size_t
> > count)
> > +{
> > +       bool res;
> > +       int ret;
> > +
> > +       ret = kstrtobool(buf, &res);
> > +       if (ret)
> > +               return ret;
> > +
> > +       if (!res)
> > +               return count;
> > +
> > +       ret = bus_for_each_dev(&peci_bus_type, NULL, NULL,
> > rescan_controller);
> > +       if (ret)
> > +               return ret;
> > +
> > +       return count;
> > +}
> > +static BUS_ATTR_WO(rescan);
> > +
> > +static struct attribute *peci_bus_attrs[] = {
> > +       &bus_attr_rescan.attr,
> > +       NULL
> > +};
> > +
> > +static const struct attribute_group peci_bus_group = {
> > +       .attrs = peci_bus_attrs,
> > +};
> > +
> > +const struct attribute_group *peci_bus_groups[] = {
> > +       &peci_bus_group,
> > +       NULL
> > +};
> > +
> > +static ssize_t remove_store(struct device *dev, struct device_attribute
> > *attr,
> > +                           const char *buf, size_t count)
> > +{
> > +       struct peci_device *device = to_peci_device(dev);
> > +       bool res;
> > +       int ret;
> > +
> > +       ret = kstrtobool(buf, &res);
> > +       if (ret)
> > +               return ret;
> > +
> > +       if (res && device_remove_file_self(dev, attr))
> > +               peci_device_destroy(device);
> 
> How do you solve races between sysfs device remove and controller
> device remove? Looks like double-free at first glance. Have a look at
> the  kill_device() helper as one way to resolve this double-delete
> race..

Done.

Thanks
-Iwona

> 
> > +
> > +       return count;
> > +}
> > +static DEVICE_ATTR_IGNORE_LOCKDEP(remove, 0200, NULL, remove_store);
> > +
> > +static struct attribute *peci_device_attrs[] = {
> > +       &dev_attr_remove.attr,
> > +       NULL
> > +};
> > +
> > +static const struct attribute_group peci_device_group = {
> > +       .attrs = peci_device_attrs,
> > +};
> > +
> > +const struct attribute_group *peci_device_groups[] = {
> > +       &peci_device_group,
> > +       NULL
> > +};
> > --
> > 2.31.1
> >