Re: [PATCH 08/14] peci: Add device detection

["Williams, Dan J" <dan.j.williams@intel.com>]

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
> +};