powerpc: Add SCOM infrastructure

SCOM is a side-band configuration bus implemented on some processors.
This code provides a way for code to map and operate on devices via
SCOM, while the details of how that is implemented is left up to a
SCOM "controller" in the platform code.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Michael Ellerman <michael@ellerman.id.au>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

1 files changed, 156 insertions, 0 deletions

diff --git a/arch/powerpc/include/asm/scom.h b/arch/powerpc/include/asm/scom.h
new file mode 100644
index 00000000000..0cabfd7bc2d
--- /dev/null
+++ b/arch/powerpc/include/asm/scom.h
@@ -0,0 +1,156 @@
+/*
+ * Copyright 2010 Benjamin Herrenschmidt, IBM Corp
+ *                <benh@kernel.crashing.org>
+ *     and        David Gibson, IBM Corporation.
+ *
+ *   This program is free software;  you can redistribute it and/or modify
+ *   it under the terms of the GNU General Public License as published by
+ *   the Free Software Foundation; either version 2 of the License, or
+ *   (at your option) any later version.
+ *
+ *   This program is distributed in the hope that it will be useful,
+ *   but WITHOUT ANY WARRANTY;  without even the implied warranty of
+ *   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See
+ *   the GNU General Public License for more details.
+ *
+ *   You should have received a copy of the GNU General Public License
+ *   along with this program;  if not, write to the Free Software
+ *   Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
+ */
+
+#ifndef _ASM_POWERPC_SCOM_H
+#define _ASM_POWERPC_SCOM_H
+
+#ifdef __KERNEL__
+#ifndef __ASSEMBLY__
+#ifdef CONFIG_PPC_SCOM
+
+/*
+ * The SCOM bus is a sideband bus used for accessing various internal
+ * registers of the processor or the chipset. The implementation details
+ * differ between processors and platforms, and the access method as
+ * well.
+ *
+ * This API allows to "map" ranges of SCOM register numbers associated
+ * with a given SCOM controller. The later must be represented by a
+ * device node, though some implementations might support NULL if there
+ * is no possible ambiguity
+ *
+ * Then, scom_read/scom_write can be used to accesses registers inside
+ * that range. The argument passed is a register number relative to
+ * the beginning of the range mapped.
+ */
+
+typedef void *scom_map_t;
+
+/* Value for an invalid SCOM map */
+#define SCOM_MAP_INVALID	(NULL)
+
+/* The scom_controller data structure is what the platform passes
+ * to the core code in scom_init, it provides the actual implementation
+ * of all the SCOM functions
+ */
+struct scom_controller {
+	scom_map_t (*map)(struct device_node *ctrl_dev, u64 reg, u64 count);
+	void (*unmap)(scom_map_t map);
+
+	u64 (*read)(scom_map_t map, u32 reg);
+	void (*write)(scom_map_t map, u32 reg, u64 value);
+};
+
+extern const struct scom_controller *scom_controller;
+
+/**
+ * scom_init - Initialize the SCOM backend, called by the platform
+ * @controller: The platform SCOM controller
+ */
+static inline void scom_init(const struct scom_controller *controller)
+{
+	scom_controller = controller;
+}
+
+/**
+ * scom_map_ok - Test is a SCOM mapping is successful
+ * @map: The result of scom_map to test
+ */
+static inline int scom_map_ok(scom_map_t map)
+{
+	return map != SCOM_MAP_INVALID;
+}
+
+/**
+ * scom_map - Map a block of SCOM registers
+ * @ctrl_dev: Device node of the SCOM controller
+ *            some implementations allow NULL here
+ * @reg: first SCOM register to map
+ * @count: Number of SCOM registers to map
+ */
+
+static inline scom_map_t scom_map(struct device_node *ctrl_dev,
+				  u64 reg, u64 count)
+{
+	return scom_controller->map(ctrl_dev, reg, count);
+}
+
+/**
+ * scom_find_parent - Find the SCOM controller for a device
+ * @dev: OF node of the device
+ *
+ * This is not meant for general usage, but in combination with
+ * scom_map() allows to map registers not represented by the
+ * device own scom-reg property. Useful for applying HW workarounds
+ * on things not properly represented in the device-tree for example.
+ */
+struct device_node *scom_find_parent(struct device_node *dev);
+
+
+/**
+ * scom_map_device - Map a device's block of SCOM registers
+ * @dev: OF node of the device
+ * @index: Register bank index (index in "scom-reg" property)
+ *
+ * This function will use the device-tree binding for SCOM which
+ * is to follow "scom-parent" properties until it finds a node with
+ * a "scom-controller" property to find the controller. It will then
+ * use the "scom-reg" property which is made of reg/count pairs,
+ * each of them having a size defined by the controller's #scom-cells
+ * property
+ */
+extern scom_map_t scom_map_device(struct device_node *dev, int index);
+
+
+/**
+ * scom_unmap - Unmap a block of SCOM registers
+ * @map: Result of scom_map is to be unmapped
+ */
+static inline void scom_unmap(scom_map_t map)
+{
+	if (scom_map_ok(map))
+		scom_controller->unmap(map);
+}
+
+/**
+ * scom_read - Read a SCOM register
+ * @map: Result of scom_map
+ * @reg: Register index within that map
+ */
+static inline u64 scom_read(scom_map_t map, u32 reg)
+{
+	return scom_controller->read(map, reg);
+}
+
+/**
+ * scom_write - Write to a SCOM register
+ * @map: Result of scom_map
+ * @reg: Register index within that map
+ * @value: Value to write
+ */
+static inline void scom_write(scom_map_t map, u32 reg, u64 value)
+{
+	scom_controller->write(map, reg, value);
+}
+
+#endif /* CONFIG_PPC_SCOM */
+#endif /* __ASSEMBLY__ */
+#endif /* __KERNEL__ */
+#endif /* _ASM_POWERPC_SCOM_H */