[Skiboot] [PATCH 02/10] Introduce hwprobe facility to avoid hard-coding probe functions

[Nicholas Piggin]

From: Stewart Smith <stewart at flamingspork.com>

hwprobe is a little system to have different hardware probing modules
run in the dependency order they choose rather than hard coding
that order in core/init.c.

Signed-off-by: Stewart Smith <stewart at flamingspork.com>
---
 core/Makefile.inc |  1 +
 core/hwprobe.c    | 70 +++++++++++++++++++++++++++++++++++++++++++++++
 core/init.c       |  3 ++
 include/skiboot.h | 39 +++++++++++++++++++++++++-
 skiboot.lds.S     |  6 ++++
 5 files changed, 118 insertions(+), 1 deletion(-)
 create mode 100644 core/hwprobe.c

diff --git a/core/Makefile.inc b/core/Makefile.inc
index 829800e5b..f80019b6a 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 += hwprobe.o
 
 ifeq ($(SKIBOOT_GCOV),1)
 CORE_OBJS += gcov-profiling.o
diff --git a/core/hwprobe.c b/core/hwprobe.c
new file mode 100644
index 000000000..de331af48
--- /dev/null
+++ b/core/hwprobe.c
@@ -0,0 +1,70 @@
+// SPDX-License-Identifier: Apache-2.0 OR GPL-2.0-or-later
+/* Copyright 2021 Stewart Smith */
+
+#define pr_fmt(fmt)  "HWPROBE: " fmt
+#include <skiboot.h>
+#include <string.h>
+
+static bool hwprobe_deps_satisfied(const struct hwprobe *hwp)
+{
+	struct hwprobe *hwprobe;
+	const char *dep;
+	unsigned int i;
+
+	if (hwp->deps == NULL)
+		return true;
+
+	dep = hwp->deps[0];
+
+	prlog(PR_TRACE, "Checking deps for %s\n", hwp->name);
+
+	while (dep != NULL) {
+		prlog(PR_TRACE, "Checking %s dep %s\n", hwp->name, dep);
+		hwprobe = &__hwprobes_start;
+		for (i = 0; &hwprobe[i] < &__hwprobes_end; i++) {
+			if(strcmp(hwprobe[i].name,dep) == 0 &&
+			   !hwprobe[i].probed)
+				return false;
+		}
+		dep++;
+	}
+
+	prlog(PR_TRACE, "deps for %s are satisfied!\n", hwp->name);
+	return true;
+
+}
+
+void probe_hardware(void)
+{
+	struct hwprobe *hwprobe;
+	unsigned int i;
+	bool work_todo = true;
+	bool did_something = true;
+
+	while (work_todo) {
+		work_todo = false;
+		did_something = false;
+		hwprobe = &__hwprobes_start;
+		prlog(PR_DEBUG, "Begin loop\n");
+		for (i = 0; &hwprobe[i] < &__hwprobes_end; i++) {
+			if (hwprobe[i].probed)
+				continue;
+			if (hwprobe_deps_satisfied(&hwprobe[i])) {
+				prlog(PR_DEBUG, "Probing %s...\n", hwprobe[i].name);
+				if (hwprobe[i].probe)
+					hwprobe[i].probe();
+				did_something = true;
+				hwprobe[i].probed = true;
+			} else {
+				prlog(PR_DEBUG, "Dependencies for %s not yet satisfied, skipping\n",
+				      hwprobe[i].name);
+				work_todo = true;
+			}
+		}
+
+		if (work_todo && !did_something) {
+			prlog(PR_ERR, "Cannot satisfy dependencies! Bailing out\n");
+			break;
+		}
+	}
+}
diff --git a/core/init.c b/core/init.c
index d5ba67edd..ed3229172 100644
--- a/core/init.c
+++ b/core/init.c
@@ -1333,6 +1333,9 @@ void __noreturn __nomcount main_cpu_entry(const void *fdt)
 	probe_npu2();
 	probe_npu3();
 
+	/* Probe all HWPROBE hardware we have code linked for*/
+	probe_hardware();
+
 	/* Initialize PCI */
 	pci_init_slots();
 
diff --git a/include/skiboot.h b/include/skiboot.h
index 331aa9501..d104c7a89 100644
--- a/include/skiboot.h
+++ b/include/skiboot.h
@@ -1,5 +1,7 @@
 // SPDX-License-Identifier: Apache-2.0 OR GPL-2.0-or-later
-/* Copyright 2013-2019 IBM Corp. */
+/* Copyright 2013-2019 IBM Corp.
+ * Copyright 2021 Stewart Smith
+ */
 
 #ifndef __SKIBOOT_H
 #define __SKIBOOT_H
@@ -342,4 +344,39 @@ extern int fake_nvram_info(uint32_t *total_size);
 extern int fake_nvram_start_read(void *dst, uint32_t src, uint32_t len);
 extern int fake_nvram_write(uint32_t offset, void *src, uint32_t size);
 
+/*
+ * A bunch of hardware needs to be probed, sometimes in a particular order.
+ * Very simple dependency graph, with a even simpler way to resolve it.
+ * But it means we can now at link time choose what hardware we support.
+ * This struct should not be defined directly but with the macros.
+ */
+struct hwprobe {
+	const char	*name;
+	void		(*probe)(void);
+
+	bool		probed;
+
+	/* NULL or NULL-terminated array of strings */
+	const char	**deps;
+};
+
+#define DEFINE_HWPROBE(__name, __probe)		\
+static const struct hwprobe __used __section(".hwprobes") hwprobe_##__name = { \
+	.name = #__name,				\
+	.probe = __probe,				\
+	.deps = NULL,					\
+}
+
+#define DEFINE_HWPROBE_DEPS(__name, __probe, ...)	\
+static const struct hwprobe __used __section(".hwprobes") hwprobe_##__name = { \
+	.name = #__name,				\
+	.probe = __probe,				\
+	.deps = (const char *[]){ __VA_ARGS__, NULL},	\
+}
+
+extern struct hwprobe __hwprobes_start;
+extern struct hwprobe __hwprobes_end;
+
+extern void probe_hardware(void);
+
 #endif /* __SKIBOOT_H */
diff --git a/skiboot.lds.S b/skiboot.lds.S
index 5a7f9e316..c8e6e747c 100644
--- a/skiboot.lds.S
+++ b/skiboot.lds.S
@@ -164,6 +164,12 @@ SECTIONS
 		__platforms_end = .;
 	}
 
+	.hwprobes : {
+		__hwprobes_start = .;
+		KEEP(*(.hwprobes))
+		__hwprobes_end = .;
+	}
+
 	/* Relocations */
 	. = ALIGN(0x10);
 	.dynamic : {
-- 
2.23.0