riscv: Allow device trees to be built into the kernel

Some systems don't provide a useful device tree to the kernel on boot.
Chasing around bootloaders for these systems is a headache, so instead
le't's just keep a device tree table in the kernel, keyed by the SOC's
unique identifier, that contains the relevant DTB.

This is only implemented for M mode right now. While we could implement
this via the SBI calls that allow access to these identifiers, we don't
have any systems that need this right now.

Signed-off-by: Palmer Dabbelt <palmerdabbelt@google.com>

1 files changed, 27 insertions, 0 deletions

diff --git a/arch/riscv/kernel/soc.c b/arch/riscv/kernel/soc.c
index 0b3b3dc9ad0f..1fc87621c728 100644
--- a/arch/riscv/kernel/soc.c
+++ b/arch/riscv/kernel/soc.c
@@ -26,3 +26,30 @@ void __init soc_early_init(void)
 		}
 	}
 }
+
+static bool soc_builtin_dtb_match(unsigned long vendor_id,
+				unsigned long arch_id, unsigned long imp_id,
+				const struct soc_builtin_dtb *entry)
+{
+	return entry->vendor_id == vendor_id &&
+	       entry->arch_id == arch_id &&
+	       entry->imp_id == imp_id;
+}
+
+void * __init soc_lookup_builtin_dtb(void)
+{
+	unsigned long vendor_id, arch_id, imp_id;
+	const struct soc_builtin_dtb *s;
+
+	__asm__ ("csrr %0, mvendorid" : "=r"(vendor_id));
+	__asm__ ("csrr %0, marchid" : "=r"(arch_id));
+	__asm__ ("csrr %0, mimpid" : "=r"(imp_id));
+
+	for (s = (void *)&__soc_builtin_dtb_table_start;
+	     (void *)s < (void *)&__soc_builtin_dtb_table_end; s++) {
+		if (soc_builtin_dtb_match(vendor_id, arch_id, imp_id, s))
+			return s->dtb_func();
+	}
+
+	return NULL;
+}