Re: [PATCH v2 08/15] peci: Add device detection

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

On Fri, 2021-08-27 at 12:01 -0700, Dan Williams wrote:
> On Tue, Aug 3, 2021 at 4:35 AM Iwona Winiarska
> <iwona.winiarska@intel.com> 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     |  33 ++++++++++++
> >  drivers/peci/device.c   | 114 ++++++++++++++++++++++++++++++++++++++++
> >  drivers/peci/internal.h |  14 +++++
> >  drivers/peci/request.c  |  50 ++++++++++++++++++
> >  5 files changed, 212 insertions(+), 1 deletion(-)
> >  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 926d8df15cbd..c5f9d3fe21bb 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
> > +peci-y := core.o request.o device.o
> >  obj-$(CONFIG_PECI) += peci.o
> > 
> >  # Hardware specific bus drivers
> > diff --git a/drivers/peci/core.c b/drivers/peci/core.c
> > index 7b3938af0396..d143f1a7fe98 100644
> > --- a/drivers/peci/core.c
> > +++ b/drivers/peci/core.c
> > @@ -34,6 +34,20 @@ struct device_type peci_controller_type = {
> >         .release        = peci_controller_dev_release,
> >  };
> > 
> > +static int peci_controller_scan_devices(struct peci_controller *controller)
> > +{
> > +       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;
> > +       }
> > +
> > +       return 0;
> > +}
> > +
> >  static struct peci_controller *peci_controller_alloc(struct device *dev,
> >                                                      struct
> > peci_controller_ops *ops)
> >  {
> > @@ -76,10 +90,23 @@ static struct peci_controller
> > *peci_controller_alloc(struct device *dev,
> >         return ERR_PTR(ret);
> >  }
> > 
> > +static int unregister_child(struct device *dev, void *dummy)
> > +{
> > +       peci_device_destroy(to_peci_device(dev));
> > +
> > +       return 0;
> > +}
> > +
> >  static void unregister_controller(void *_controller)
> >  {
> >         struct peci_controller *controller = _controller;
> > 
> > +       /*
> > +        * Detach any active PECI devices. This can't fail, thus we do not
> > +        * check the returned value.
> > +        */
> > +       device_for_each_child_reverse(&controller->dev, NULL,
> > unregister_child);
> > +
> >         device_unregister(&controller->dev);
> >  }
> > 
> > @@ -115,6 +142,12 @@ struct peci_controller *devm_peci_controller_add(struct
> > device *dev,
> >         if (ret)
> >                 return ERR_PTR(ret);
> > 
> > +       /*
> > +        * Ignoring retval since failures during scan are non-critical for
> > +        * controller itself.
> > +        */
> > +       peci_controller_scan_devices(controller);
> > +
> >         return controller;
> > 
> >  err:
> > diff --git a/drivers/peci/device.c b/drivers/peci/device.c
> > new file mode 100644
> > index 000000000000..32811248997b
> > --- /dev/null
> > +++ b/drivers/peci/device.c
> > @@ -0,0 +1,114 @@
> > +// 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;
> > +
> > +       /*
> > +        * PECI Ping is a command encoded by tx_len = 0, rx_len = 0.
> > +        * We expect correct Write FCS if the device at the target address
> > +        * is able to respond.
> > +        */
> > +       req = peci_request_alloc(NULL, 0, 0);
> > +       if (!req)
> > +               return -ENOMEM;
> 
> Seems a waste to do a heap allocation for this routine. Why not:
> 
>        /*
>         * PECI Ping is a command encoded by tx_len = 0, rx_len = 0.
>         * We expect correct Write FCS if the device at the target address
>         * is able to respond.
>         */
>        struct peci_request req = { 0 };

Done.

> 
> > +
> > +       mutex_lock(&controller->bus_lock);
> > +       ret = controller->ops->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)))
> 
> The WARN_ON is overkill, especially as there is only one caller of
> this and it loops through valid addresses.

Done.

> 
> > +               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->addr = addr;
> > +       device->dev.parent = &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;
> 
> It's cleaner to just have one unified error exit using put_device().
> Use the device_initialize() + device_add() pattern, not
> device_register().

Done.

> 
> 
> > +
> > +       ret = device_register(&device->dev);
> > +       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);
> 
> No clear value for this wrapper, in fact in one caller it causes it to
> do a to_peci_device() just this helper can undo that up-cast.

It gains value after extending it with kill_device().

> 
> > +}
> > +
> > +static void peci_device_release(struct device *dev)
> > +{
> > +       struct peci_device *device = to_peci_device(dev);
> > +
> > +       kfree(device);
> > +}
> > +
> > +struct device_type peci_device_type = {
> > +       .release        = peci_device_release,
> > +};
> > diff --git a/drivers/peci/internal.h b/drivers/peci/internal.h
> > index 918dea745a86..57d11a902c5d 100644
> > --- a/drivers/peci/internal.h
> > +++ b/drivers/peci/internal.h
> > @@ -8,6 +8,20 @@
> >  #include <linux/types.h>
> > 
> >  struct peci_controller;
> > +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;
> > +
> > +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;
> > 
> > diff --git a/drivers/peci/request.c b/drivers/peci/request.c
> > new file mode 100644
> > index 000000000000..81b567bc7b87
> > --- /dev/null
> > +++ b/drivers/peci/request.c
> > @@ -0,0 +1,50 @@
> > +// 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_requests
> > + * @device: PECI device to which request is going to be sent
> > + * @tx_len: TX length
> > + * @rx_len: RX 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)
> > +{
> > +       struct peci_request *req;
> > +
> > +       if (WARN_ON_ONCE(tx_len > PECI_REQUEST_MAX_BUF_SIZE || rx_len >
> > PECI_REQUEST_MAX_BUF_SIZE))
> 
> WARN_ON_ONCE() should only be here to help other kernel developers not
> make this mistake However, another way to enforce this is to stop
> exporting peci_request_alloc() and instead export helpers for specific
> command types, and keep this detail internal to the core. If you keep
> this, it needs a comment that it is only here to warn other
> peci-client developers of their bug before it goes upstream.

Added comment.

Thanks
-Iwona