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

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

On Wed, 2021-07-14 at 21:05 +0000, Williams, Dan J wrote:
> 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?
> 

peci_controller_add() is expected to be called during probe() of
controller driver (otherwise the driver isn't really a controller
driver).


> >         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().
> 

Ack.

> > +
> >         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?
> 

It's PECI wire (physical layer) interface limitation.

> > +       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
> 

It's just kfree in this case, but I agree. I'll modify this.

> > +       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?

PECI specification defines tx_len as a single byte, same thing for
rx_len.
Currently the largest we're using is 24 IIRC.

> 
> > +       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?

Symmetry with adding devices (in this case rescan) - it's also useful
for development and testing (e.g. kick off extra devices to leave a
single one).
Moreover, it looks like common pattern in other subsystems.

Thank you
-Iwona

> 
> > +
> > +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
> > +};
>