Merge tag 'stm32-bus-firewall-for-v6.10-1' of git://git.kernel.org/pub/scm/linux/kernel/git/atorgue/stm32 into soc/drivers

STM32 Firewall bus for v6.10, round 1

Highlights:
---------

Introduce STM32 Firewall framework for STM32MP1x and STM32MP2x
platforms. STM32MP1x(ETZPC) and STM32MP2x(RIFSC) Firewall controllers
register to the framework to offer firewall services such as access
granting.

This series of patches is a new approach on the previous STM32 system
bus, history is available here:
https://lore.kernel.org/lkml/20230127164040.1047583/

The need for such framework arises from the fact that there are now
multiple hardware firewalls implemented across multiple products.
Drivers are shared between different products, using the same code.
When it comes to firewalls, the purpose mostly stays the same: Protect
hardware resources. But the implementation differs, and there are
multiple types of firewalls: peripheral, memory, ...

Some hardware firewall controllers such as the RIFSC implemented on
STM32MP2x platforms may require to take ownership of a resource before
being able to use it, hence the requirement for firewall services to
take/release the ownership of such resources.

On the other hand, hardware firewall configurations are becoming
more and more complex. These mecanisms prevent platform crashes
or other firewall-related incoveniences by denying access to some
resources.

The stm32 firewall framework offers an API that is defined in
firewall controllers drivers to best fit the specificity of each
firewall.

For every peripherals protected by either the ETZPC or the RIFSC, the
firewall framework checks the firewall controlelr registers to see if
the peripheral's access is granted to the Linux kernel. If not, the
peripheral is configured as secure, the node is marked populated,
so that the driver is not probed for that device.

The firewall framework relies on the access-controller device tree
binding. It is used by peripherals to reference a domain access
controller. In this case a firewall controller. The bus uses the ID
referenced by the access-controller property to know where to look
in the firewall to get the security configuration for the peripheral.
This allows a device tree description rather than a hardcoded peripheral
table in the bus driver.

The STM32 ETZPC device is responsible for filtering accesses based on
security level, or co-processor isolation for any resource connected
to it.

The RIFSC is responsible for filtering accesses based on Compartment
ID / security level / privilege level for any resource connected to
it.

* tag 'stm32-bus-firewall-for-v6.10-1' of git://git.kernel.org/pub/scm/linux/kernel/git/atorgue/stm32:
  bus: stm32_firewall: fix off by one in stm32_firewall_get_firewall()
  bus: etzpc: introduce ETZPC firewall controller driver
  bus: rifsc: introduce RIFSC firewall controller driver
  of: property: fw_devlink: Add support for "access-controller"
  firewall: introduce stm32_firewall framework
  dt-bindings: bus: document ETZPC
  dt-bindings: bus: document RIFSC
  dt-bindings: treewide: add access-controllers description
  dt-bindings: document generic access controllers

Link: https://lore.kernel.org/r/7dc64226-5429-4ab7-a8c8-6053b12e3cf5@foss.st.com
Signed-off-by: Arnd Bergmann <arnd@arndb.de>

1 files changed, 142 insertions, 0 deletions

diff --git a/include/linux/bus/stm32_firewall_device.h b/include/linux/bus/stm32_firewall_device.h
new file mode 100644
index 000000000000..18e0a2fc3816
--- /dev/null
+++ b/include/linux/bus/stm32_firewall_device.h
@@ -0,0 +1,142 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Copyright (C) 2023, STMicroelectronics - All Rights Reserved
+ */
+
+#ifndef STM32_FIREWALL_DEVICE_H
+#define STM32_FIREWALL_DEVICE_H
+
+#include <linux/of.h>
+#include <linux/platform_device.h>
+#include <linux/types.h>
+
+#define STM32_FIREWALL_MAX_EXTRA_ARGS		5
+
+/* Opaque reference to stm32_firewall_controller */
+struct stm32_firewall_controller;
+
+/**
+ * struct stm32_firewall - Information on a device's firewall. Each device can have more than one
+ *			   firewall.
+ *
+ * @firewall_ctrl:		Pointer referencing a firewall controller of the device. It is
+ *				opaque so a device cannot manipulate the controller's ops or access
+ *				the controller's data
+ * @extra_args:			Extra arguments that are implementation dependent
+ * @entry:			Name of the firewall entry
+ * @extra_args_size:		Number of extra arguments
+ * @firewall_id:		Firewall ID associated the device for this firewall controller
+ */
+struct stm32_firewall {
+	struct stm32_firewall_controller *firewall_ctrl;
+	u32 extra_args[STM32_FIREWALL_MAX_EXTRA_ARGS];
+	const char *entry;
+	size_t extra_args_size;
+	u32 firewall_id;
+};
+
+#if IS_ENABLED(CONFIG_STM32_FIREWALL)
+/**
+ * stm32_firewall_get_firewall - Get the firewall(s) associated to given device.
+ *				 The firewall controller reference is always the first argument
+ *				 of each of the access-controller property entries.
+ *				 The firewall ID is always the second argument of each of the
+ *				 access-controller  property entries.
+ *				 If there's no argument linked to the phandle, then the firewall ID
+ *				 field is set to U32_MAX, which is an invalid ID.
+ *
+ * @np:				Device node to parse
+ * @firewall:			Array of firewall references
+ * @nb_firewall:		Number of firewall references to get. Must be at least 1.
+ *
+ * Returns 0 on success, -ENODEV if there's no match with a firewall controller or appropriate errno
+ * code if error occurred.
+ */
+int stm32_firewall_get_firewall(struct device_node *np, struct stm32_firewall *firewall,
+				unsigned int nb_firewall);
+
+/**
+ * stm32_firewall_grant_access - Request firewall access rights and grant access.
+ *
+ * @firewall:			Firewall reference containing the ID to check against its firewall
+ *				controller
+ *
+ * Returns 0 if access is granted, -EACCES if access is denied, -ENODEV if firewall is null or
+ * appropriate errno code if error occurred
+ */
+int stm32_firewall_grant_access(struct stm32_firewall *firewall);
+
+/**
+ * stm32_firewall_release_access - Release access granted from a call to
+ *				   stm32_firewall_grant_access().
+ *
+ * @firewall:			Firewall reference containing the ID to check against its firewall
+ *				controller
+ */
+void stm32_firewall_release_access(struct stm32_firewall *firewall);
+
+/**
+ * stm32_firewall_grant_access_by_id - Request firewall access rights of a given device
+ *				       based on a specific firewall ID
+ *
+ * Warnings:
+ * There is no way to ensure that the given ID will correspond to the firewall referenced in the
+ * device node if the ID did not come from stm32_firewall_get_firewall(). In that case, this
+ * function must be used with caution.
+ * This function should be used for subsystem resources that do not have the same firewall ID
+ * as their parent.
+ * U32_MAX is an invalid ID.
+ *
+ * @firewall:			Firewall reference containing the firewall controller
+ * @subsystem_id:		Firewall ID of the subsystem resource
+ *
+ * Returns 0 if access is granted, -EACCES if access is denied, -ENODEV if firewall is null or
+ * appropriate errno code if error occurred
+ */
+int stm32_firewall_grant_access_by_id(struct stm32_firewall *firewall, u32 subsystem_id);
+
+/**
+ * stm32_firewall_release_access_by_id - Release access granted from a call to
+ *					 stm32_firewall_grant_access_by_id().
+ *
+ * Warnings:
+ * There is no way to ensure that the given ID will correspond to the firewall referenced in the
+ * device node if the ID did not come from stm32_firewall_get_firewall(). In that case, this
+ * function must be used with caution.
+ * This function should be used for subsystem resources that do not have the same firewall ID
+ * as their parent.
+ * U32_MAX is an invalid ID.
+ *
+ * @firewall:			Firewall reference containing the firewall controller
+ * @subsystem_id:		Firewall ID of the subsystem resource
+ */
+void stm32_firewall_release_access_by_id(struct stm32_firewall *firewall, u32 subsystem_id);
+
+#else /* CONFIG_STM32_FIREWALL */
+
+int stm32_firewall_get_firewall(struct device_node *np, struct stm32_firewall *firewall,
+				unsigned int nb_firewall);
+{
+	return -ENODEV;
+}
+
+int stm32_firewall_grant_access(struct stm32_firewall *firewall)
+{
+	return -ENODEV;
+}
+
+void stm32_firewall_release_access(struct stm32_firewall *firewall)
+{
+}
+
+int stm32_firewall_grant_access_by_id(struct stm32_firewall *firewall, u32 subsystem_id)
+{
+	return -ENODEV;
+}
+
+void stm32_firewall_release_access_by_id(struct stm32_firewall *firewall, u32 subsystem_id)
+{
+}
+
+#endif /* CONFIG_STM32_FIREWALL */
+#endif /* STM32_FIREWALL_DEVICE_H */