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    SubjectRe: [PATCH 08/14] peci: Add device detection
    Date
    On Tue, 2021-07-13 at 00:04 +0200, Iwona Winiarska wrote:
    > Since PECI devices are discoverable, we can dynamically detect devices
    > that are actually available in the system.
    >
    > This change complements the earlier implementation by rescanning PECI
    > bus to detect available devices. For this purpose, it also introduces the
    > minimal API for PECI requests.
    >
    > Signed-off-by: Iwona Winiarska <iwona.winiarska@intel.com>
    > Reviewed-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
    > ---
    >  drivers/peci/Makefile   |   2 +-
    >  drivers/peci/core.c     |  13 ++++-
    >  drivers/peci/device.c   | 111 ++++++++++++++++++++++++++++++++++++++++
    >  drivers/peci/internal.h |  15 ++++++
    >  drivers/peci/request.c  |  74 +++++++++++++++++++++++++++
    >  drivers/peci/sysfs.c    |  34 ++++++++++++
    >  6 files changed, 246 insertions(+), 3 deletions(-)
    >  create mode 100644 drivers/peci/device.c
    >  create mode 100644 drivers/peci/request.c
    >
    > diff --git a/drivers/peci/Makefile b/drivers/peci/Makefile
    > index 621a993e306a..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 sysfs.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 0ad00110459d..ae7a9572cdf3 100644
    > --- a/drivers/peci/core.c
    > +++ b/drivers/peci/core.c
    > @@ -31,7 +31,15 @@ struct device_type peci_controller_type = {
    >  
    >  int peci_controller_scan_devices(struct peci_controller *controller)
    >  {
    > -       /* Just a stub, no support for actual devices yet */
    > +       int ret;
    > +       u8 addr;
    > +
    > +       for (addr = PECI_BASE_ADDR; addr < PECI_BASE_ADDR + PECI_DEVICE_NUM_MAX; addr++) {
    > +               ret = peci_device_create(controller, addr);
    > +               if (ret)
    > +                       return ret;
    > +       }
    > +

    This seems to be a behavior triggered at peci_controller_add and at the
    request of userspace when touching the rescan attribute? A natural way
    to handle this would be to have a driver for the peci_controller device
    and have that driver issue scan at probe time. Otherwise, how does
    userspace know when it is time to rescan the bus?

    >         return 0;
    >  }
    >  
    > @@ -106,7 +114,8 @@ EXPORT_SYMBOL_NS_GPL(peci_controller_add, PECI);
    >  
    >  static int _unregister(struct device *dev, void *dummy)
    >  {
    > -       /* Just a stub, no support for actual devices yet */
    > +       peci_device_destroy(to_peci_device(dev));

    As mentioned previously, this could be delegated to devm to unregister
    when the original driver that added the controller goes through -
    >remove().

    > +
    >         return 0;
    >  }
    >  
    > diff --git a/drivers/peci/device.c b/drivers/peci/device.c
    > new file mode 100644
    > index 000000000000..1124862211e2
    > --- /dev/null
    > +++ b/drivers/peci/device.c
    > @@ -0,0 +1,111 @@
    > +// SPDX-License-Identifier: GPL-2.0-only
    > +// Copyright (c) 2018-2021 Intel Corporation
    > +
    > +#include <linux/peci.h>
    > +#include <linux/slab.h>
    > +
    > +#include "internal.h"
    > +
    > +static int peci_detect(struct peci_controller *controller, u8 addr)
    > +{
    > +       struct peci_request *req;
    > +       int ret;
    > +
    > +       req = peci_request_alloc(NULL, 0, 0);
    > +       if (!req)
    > +               return -ENOMEM;
    > +
    > +       mutex_lock(&controller->bus_lock);

    What is the underlying requirement to prevent 2 simultaneous ->xfer()
    invocations?

    > +       ret = controller->xfer(controller, addr, req);
    > +       mutex_unlock(&controller->bus_lock);
    > +
    > +       peci_request_free(req);
    > +
    > +       return ret;
    > +}
    > +
    > +static bool peci_addr_valid(u8 addr)
    > +{
    > +       return addr >= PECI_BASE_ADDR && addr < PECI_BASE_ADDR + PECI_DEVICE_NUM_MAX;
    > +}
    > +
    > +static int peci_dev_exists(struct device *dev, void *data)
    > +{
    > +       struct peci_device *device = to_peci_device(dev);
    > +       u8 *addr = data;
    > +
    > +       if (device->addr == *addr)
    > +               return -EBUSY;
    > +
    > +       return 0;
    > +}
    > +
    > +int peci_device_create(struct peci_controller *controller, u8 addr)
    > +{
    > +       struct peci_device *device;
    > +       int ret;
    > +
    > +       if (WARN_ON(!peci_addr_valid(addr)))
    > +               return -EINVAL;
    > +
    > +       /* Check if we have already detected this device before. */
    > +       ret = device_for_each_child(&controller->dev, &addr, peci_dev_exists);
    > +       if (ret)
    > +               return 0;
    > +
    > +       ret = peci_detect(controller, addr);
    > +       if (ret) {
    > +               /*
    > +                * Device not present or host state doesn't allow successful
    > +                * detection at this time.
    > +                */
    > +               if (ret == -EIO || ret == -ETIMEDOUT)
    > +                       return 0;
    > +
    > +               return ret;
    > +       }
    > +
    > +       device = kzalloc(sizeof(*device), GFP_KERNEL);
    > +       if (!device)
    > +               return -ENOMEM;
    > +
    > +       device->controller = controller;
    > +       device->addr = addr;
    > +       device->dev.parent = &device->controller->dev;
    > +       device->dev.bus = &peci_bus_type;
    > +       device->dev.type = &peci_device_type;
    > +
    > +       ret = dev_set_name(&device->dev, "%d-%02x", controller->id, device->addr);
    > +       if (ret)
    > +               goto err_free;
    > +
    > +       ret = device_register(&device->dev);

    There is a recent movement away from device_register() to an alloc+add
    pattern [1]. I.e. have device_initialize() and device_add() steps. With
    that you can unify the error exit to be put_device().

    [1]: https://lore.kernel.org/r/20210712134233.GA141137@ziepe.ca

    > +       if (ret)
    > +               goto err_put;
    > +
    > +       return 0;
    > +
    > +err_put:
    > +       put_device(&device->dev);
    > +err_free:
    > +       kfree(device);
    > +
    > +       return ret;
    > +}
    > +
    > +void peci_device_destroy(struct peci_device *device)
    > +{
    > +       device_unregister(&device->dev);
    > +}
    > +
    > +static void peci_device_release(struct device *dev)
    > +{
    > +       struct peci_device *device = to_peci_device(dev);
    > +
    > +       kfree(device);
    > +}
    > +
    > +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 80c61bcdfc6b..6b139adaf6b8 100644
    > --- a/drivers/peci/internal.h
    > +++ b/drivers/peci/internal.h
    > @@ -9,6 +9,21 @@
    >  
    >  struct peci_controller;
    >  struct attribute_group;
    > +struct peci_device;
    > +struct peci_request;
    > +
    > +/* PECI CPU address range 0x30-0x37 */
    > +#define PECI_BASE_ADDR         0x30
    > +#define PECI_DEVICE_NUM_MAX            8
    > +
    > +struct peci_request *peci_request_alloc(struct peci_device *device, u8 tx_len, u8 rx_len);
    > +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[];
    > diff --git a/drivers/peci/request.c b/drivers/peci/request.c
    > new file mode 100644
    > index 000000000000..78cee51dfae1
    > --- /dev/null
    > +++ b/drivers/peci/request.c
    > @@ -0,0 +1,74 @@
    > +// SPDX-License-Identifier: GPL-2.0-only
    > +// Copyright (c) 2021 Intel Corporation
    > +
    > +#include <linux/export.h>
    > +#include <linux/peci.h>
    > +#include <linux/slab.h>
    > +#include <linux/types.h>
    > +
    > +#include "internal.h"
    > +
    > +/**
    > + * peci_request_alloc() - allocate &struct peci_request with buffers with given lengths
    > + * @device: PECI device to which request is going to be sent
    > + * @tx_len: requested TX buffer length
    > + * @rx_len: requested RX buffer length
    > + *
    > + * Return: A pointer to a newly allocated &struct peci_request on success or NULL otherwise.
    > + */
    > +struct peci_request *peci_request_alloc(struct peci_device *device, u8 tx_len, u8 rx_len)
    > +{

    How big can these lengths be?

    > +       struct peci_request *req;
    > +       u8 *tx_buf, *rx_buf;
    > +
    > +       req = kzalloc(sizeof(*req), GFP_KERNEL);
    > +       if (!req)
    > +               return NULL;
    > +
    > +       req->device = device;
    > +
    > +       /*
    > +        * PECI controllers that we are using now don't support DMA, this
    > +        * should be converted to DMA API once support for controllers that do
    > +        * allow it is added to avoid an extra copy.
    > +        */
    > +       if (tx_len) {
    > +               tx_buf = kzalloc(tx_len, GFP_KERNEL);
    > +               if (!tx_buf)
    > +                       goto err_free_req;
    > +
    > +               req->tx.buf = tx_buf;
    > +               req->tx.len = tx_len;
    > +       }
    > +
    > +       if (rx_len) {
    > +               rx_buf = kzalloc(rx_len, GFP_KERNEL);
    > +               if (!rx_buf)
    > +                       goto err_free_tx;
    > +
    > +               req->rx.buf = rx_buf;
    > +               req->rx.len = rx_len;
    > +       }
    > +
    > +       return req;
    > +
    > +err_free_tx:
    > +       kfree(req->tx.buf);
    > +err_free_req:
    > +       kfree(req);
    > +
    > +       return NULL;
    > +}
    > +EXPORT_SYMBOL_NS_GPL(peci_request_alloc, PECI);
    > +
    > +/**
    > + * peci_request_free() - free peci_request
    > + * @req: the PECI request to be freed
    > + */
    > +void peci_request_free(struct peci_request *req)
    > +{
    > +       kfree(req->rx.buf);
    > +       kfree(req->tx.buf);
    > +       kfree(req);
    > +}
    > +EXPORT_SYMBOL_NS_GPL(peci_request_free, PECI);
    > diff --git a/drivers/peci/sysfs.c b/drivers/peci/sysfs.c
    > index 36c5e2a18a92..db9ef05776e3 100644
    > --- a/drivers/peci/sysfs.c
    > +++ b/drivers/peci/sysfs.c
    > @@ -1,6 +1,8 @@
    >  // 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"
    > @@ -46,3 +48,35 @@ 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);
    > +
    > +       return count;
    > +}
    > +static DEVICE_ATTR_IGNORE_LOCKDEP(remove, 0200, NULL, remove_store);

    Why does userspace need the ability to kick devices off the bus?

    Do you have an example userspace tool that is using these sysfs APIs?

    > +
    > +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
    > +};

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