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Date: Mon, 15 Nov 2021 22:19:04 +0000
From: "Winiarska, Iwona" <iwona.winiarska@...el.com>
To: "Williams, Dan J" <dan.j.williams@...el.com>
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Subject: Re: [PATCH v2 09/15] peci: Add sysfs interface for PECI bus
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@...el.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@...el.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@...el.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@...el.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
> >
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