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

[Zev Weiss <zweiss@equinix.com>]

On Mon, Jul 12, 2021 at 05:04:41PM CDT, 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;
>+	}
>+
> 	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));
>+
> 	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;
>+

Might be worth a brief comment here noting that an empty request happens
to be the format of a PECI ping command (and/or change the name of the
function to peci_ping()).

>+	mutex_lock(&controller->bus_lock);
>+	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;

Wondering about the necessity of this check (and the peci_addr_valid()
function) -- as of the end of this patch series, there's only one caller
of peci_device_create(), and it's peci_controller_scan_devices() looping
from PECI_BASE_ADDR to PECI_BASE_ADDR + PECI_DEVICE_NUM_MAX, so
checking that the address is in that range seems a bit redundant.  Do we
anticipate that we might gain additional callers in the future that
could run a non-zero risk of passing a bad address?

>+
>+	/* 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;

Do we really want to be ignoring EIO here?  From a look at
aspeed_peci_xfer(), it looks like the only path that would produce that
is the non-timeout, non-CMD_DONE case, which I guess happens on
contention or FCS errors and such.  Should we maybe have some automatic
(limited) retry loop for cases like those?

>+
>+		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);
>+	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)
>+{
>+	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;
>+	}
>+

As long as we're punting on DMA support, could we do the whole thing in
a single allocation instead of three?  It'd add some pointer arithmetic,
but would also simplify the error-handling/deallocation paths a bit.

Or, given that the one controller we're currently supporting has a
hardware limit of 32 bytes per transfer anyway, maybe just inline
fixed-size rx/tx buffers into struct peci_request and have callers keep
them on the stack instead of kmalloc()-ing them?

>+	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);
>+
>+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
>