[Skiboot] [RFC PATCH 1/6] core: Add debugfs framework

[Cédric Le Goater]

This is a very simplistic framework adding a read/write interface to
opal drivers. Drivers should define a set of 'opal_debug' handlers,
each with custom read/write operations. The device tree is then
populated with nodes such as :

	debug at 0 {
		ibm,chip-id = <0x00>;
		label = "xive-ivt";
		compatible = "ibm,opal-debug";
		reg = <0x00>;
		phandle = <0x805e>;
	};

which can be freely extended by the driver if needed.

The Linux driver can choose to expose the contents of each 'opal_debug'
handler through debugfs using the OPAL_DEBUG_READ call. It is relatively
easy to implement a simple command interface with the OPAL_DEBUG_WRITE
call, to set some values or reset some counters.

Signed-off-by: Cédric Le Goater <clg at kaod.org>
---
 include/opal-api.h   |  4 ++-
 include/opal-debug.h | 26 ++++++++++++++
 core/opal-debug.c    | 85 ++++++++++++++++++++++++++++++++++++++++++++
 core/Makefile.inc    |  1 +
 4 files changed, 115 insertions(+), 1 deletion(-)
 create mode 100644 include/opal-debug.h
 create mode 100644 core/opal-debug.c

diff --git a/include/opal-api.h b/include/opal-api.h
index e90cab1e9f65..03c414946651 100644
--- a/include/opal-api.h
+++ b/include/opal-api.h
@@ -227,7 +227,9 @@
 #define OPAL_SECVAR_ENQUEUE_UPDATE		178
 #define OPAL_PHB_SET_OPTION			179
 #define OPAL_PHB_GET_OPTION			180
-#define OPAL_LAST				180
+#define OPAL_DEBUG_READ				181
+#define OPAL_DEBUG_WRITE			182
+#define OPAL_LAST				182
 
 #define QUIESCE_HOLD			1 /* Spin all calls at entry */
 #define QUIESCE_REJECT			2 /* Fail all calls with OPAL_BUSY */
diff --git a/include/opal-debug.h b/include/opal-debug.h
new file mode 100644
index 000000000000..49d58256af7c
--- /dev/null
+++ b/include/opal-debug.h
@@ -0,0 +1,26 @@
+// SPDX-License-Identifier: Apache-2.0
+/* Copyright 2020 IBM Corp. */
+
+#ifndef __OPAL_DEBUG_H
+#define __OPAL_DEBUG_H
+
+struct opal_debug;
+
+struct opal_debug_ops {
+	const char *compat;
+	int  (*read)(struct opal_debug *d, void *buf, uint64_t size);
+	int  (*write)(struct opal_debug *d, void *buf, uint64_t size);
+};
+
+struct opal_debug {
+	const char *name;
+	void *private;
+	struct dt_node *node;
+	const struct opal_debug_ops *ops;
+};
+
+
+extern struct opal_debug *opal_debug_create(const char *name,
+			    const struct opal_debug_ops *ops, void* private);
+
+#endif
diff --git a/core/opal-debug.c b/core/opal-debug.c
new file mode 100644
index 000000000000..770489e3031c
--- /dev/null
+++ b/core/opal-debug.c
@@ -0,0 +1,85 @@
+// SPDX-License-Identifier: Apache-2.0
+/* Copyright 2020 IBM Corp. */
+
+#define pr_fmt(fmt) "DEBUG: " fmt
+
+#include <cpu.h>
+#include <opal.h>
+#include <opal-debug.h>
+
+#define OPAL_DEBUG_MAX 100
+
+static struct dt_node *opal_debug_node;
+static int opal_debug_index;
+static struct opal_debug opal_debug_handlers[OPAL_DEBUG_MAX];
+
+extern struct opal_debug *opal_debug_create(const char *name,
+			    const struct opal_debug_ops *ops, void* private)
+{
+	const char *compat = ops->compat ? ops->compat : "ibm,opal-debug";
+	struct opal_debug *d;
+
+	if (opal_debug_index == OPAL_DEBUG_MAX) {
+		prlog(PR_ERR, "Maximum number of handlers reached: %d\n",
+			OPAL_DEBUG_MAX);
+		return NULL;
+	}
+
+	d = &opal_debug_handlers[opal_debug_index];
+	d->name = name;
+	d->private = private;
+	d->ops = ops;
+
+	if (!opal_debug_node) {
+		opal_debug_node = dt_new_check(opal_node, "debug");
+		dt_add_property_cells(opal_debug_node, "#address-cells", 0);
+		dt_add_property_cells(opal_debug_node, "#size-cells", 0);
+	}
+
+	d->node = dt_new_addr(opal_debug_node, "debug", opal_debug_index);
+	dt_add_property_cells(d->node, "reg", opal_debug_index);
+	dt_add_property_string(d->node, "compatible", compat);
+	dt_add_property_string(d->node, "label", d->name);
+
+	opal_debug_index++;
+
+	return d;
+}
+
+static int64_t opal_debug_read(uint64_t id, uint64_t buf, uint64_t size)
+{
+	struct opal_debug *d;
+
+	if (id >= opal_debug_index)
+		return OPAL_PARAMETER;
+
+	d = &opal_debug_handlers[id];
+
+	if (!opal_addr_valid((void *)buf) || !size)
+		return OPAL_PARAMETER;
+
+	if (!d->ops->read)
+		return OPAL_INTERNAL_ERROR;
+
+	return d->ops->read(d, (void *)buf, size);
+}
+opal_call(OPAL_DEBUG_READ, opal_debug_read, 3);
+
+static int64_t opal_debug_write(uint64_t id, uint64_t buf, uint64_t size)
+{
+	struct opal_debug *d;
+
+	if (id >= opal_debug_index)
+		return OPAL_PARAMETER;
+
+	d = &opal_debug_handlers[id];
+
+	if (!opal_addr_valid((void *)buf) || !size)
+		return OPAL_PARAMETER;
+
+	if (!d->ops->write)
+		return OPAL_INTERNAL_ERROR;
+
+	return d->ops->write(d, (void *)buf, size);
+}
+opal_call(OPAL_DEBUG_WRITE, opal_debug_write, 3);
diff --git a/core/Makefile.inc b/core/Makefile.inc
index 829800e5b27f..ed7003ed7a7a 100644
--- a/core/Makefile.inc
+++ b/core/Makefile.inc
@@ -13,6 +13,7 @@ CORE_OBJS += timer.o i2c.o rtc.o flash.o sensor.o ipmi-opal.o
 CORE_OBJS += flash-subpartition.o bitmap.o buddy.o pci-quirk.o powercap.o psr.o
 CORE_OBJS += pci-dt-slot.o direct-controls.o cpufeatures.o
 CORE_OBJS += flash-firmware-versions.o opal-dump.o
+CORE_OBJS += opal-debug.o
 
 ifeq ($(SKIBOOT_GCOV),1)
 CORE_OBJS += gcov-profiling.o
-- 
2.25.4