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Message-ID: <CAPcyv4hhtTi+dKspjoamYj53GxT4Ot_1pG5-eavUJdihD8iAEg@mail.gmail.com>
Date: Fri, 27 Aug 2021 12:11:00 -0700
From: Dan Williams <dan.j.williams@...el.com>
To: Iwona Winiarska <iwona.winiarska@...el.com>
Cc: Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
openbmc@...ts.ozlabs.org,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
X86 ML <x86@...nel.org>,
Device Tree <devicetree@...r.kernel.org>,
linux-aspeed@...ts.ozlabs.org,
Linux ARM <linux-arm-kernel@...ts.infradead.org>,
linux-hwmon@...r.kernel.org,
Linux Doc Mailing List <linux-doc@...r.kernel.org>,
Rob Herring <robh+dt@...nel.org>,
Joel Stanley <joel@....id.au>,
Andrew Jeffery <andrew@...id.au>,
Jean Delvare <jdelvare@...e.com>,
Guenter Roeck <linux@...ck-us.net>,
Arnd Bergmann <arnd@...db.de>, Olof Johansson <olof@...om.net>,
Jonathan Corbet <corbet@....net>,
Thomas Gleixner <tglx@...utronix.de>,
Andy Lutomirski <luto@...nel.org>,
Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
Yazen Ghannam <yazen.ghannam@....com>,
Mauro Carvalho Chehab <mchehab@...nel.org>,
Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>,
Tony Luck <tony.luck@...el.com>,
Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
Jae Hyun Yoo <jae.hyun.yoo@...ux.intel.com>,
Randy Dunlap <rdunlap@...radead.org>,
Zev Weiss <zweiss@...inix.com>,
David Muller <d.mueller@...oft.ch>
Subject: Re: [PATCH v2 09/15] peci: Add sysfs interface for PECI bus
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.
>
> 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..
> +
> + 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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