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>

diff --git a/arch/riscv/Kbuild b/arch/riscv/Kbuild
index d1d0aa7..4614c01 100644 (file)
--- a/arch/riscv/Kbuild
+++ b/arch/riscv/Kbuild
@@ -1,3 +1,4 @@
 # SPDX-License-Identifier: GPL-2.0-only
 
 obj-y += kernel/ mm/ net/
+obj-$(CONFIG_BUILTIN_DTB) += boot/dts/

diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
index a31e1a4..539cd44 100644 (file)
--- a/arch/riscv/Kconfig
+++ b/arch/riscv/Kconfig
@@ -381,6 +381,11 @@ endchoice
 
 endmenu
 
+config BUILTIN_DTB
+       def_bool n
+       depends on RISCV_M_MODE
+       depends on OF
+
 menu "Power management options"
 
 source "kernel/power/Kconfig"

diff --git a/arch/riscv/include/asm/soc.h b/arch/riscv/include/asm/soc.h
index 7cec196..136a442 100644 (file)
--- a/arch/riscv/include/asm/soc.h
+++ b/arch/riscv/include/asm/soc.h
@@ -1,6 +1,7 @@
 /* SPDX-License-Identifier: GPL-2.0-or-later */
 /*
  * Copyright (C) 2020 Western Digital Corporation or its affiliates.
+ * Copyright (C) 2020 Google, Inc
  */
 
 #ifndef _ASM_RISCV_SOC_H
@@ -20,4 +21,42 @@ void soc_early_init(void);
 extern unsigned long __soc_early_init_table_start;
 extern unsigned long __soc_early_init_table_end;
 
+/*
+ * Allows Linux to provide a device tree, which is necessary for SOCs that
+ * don't provide a useful one on their own.
+ */
+struct soc_builtin_dtb {
+       unsigned long vendor_id;
+       unsigned long arch_id;
+       unsigned long imp_id;
+       void *(*dtb_func)(void);
+};
+
+/*
+ * The argument name must specify a valid DTS file name without the dts
+ * extension.
+ */
+#define SOC_BUILTIN_DTB_DECLARE(name, vendor, arch, impl)              \
+       extern void *__dtb_##name##_begin;                              \
+                                                                       \
+       static __init __used                                            \
+       void *__soc_builtin_dtb_f__##name(void)                         \
+       {                                                               \
+               return (void *)&__dtb_##name##_begin;                   \
+       }                                                               \
+                                                                       \
+       static const struct soc_builtin_dtb __soc_builtin_dtb__##name   \
+               __used __section(__soc_builtin_dtb_table) =             \
+       {                                                               \
+               .vendor_id = vendor,                                    \
+               .arch_id   = arch,                                      \
+               .imp_id    = impl,                                      \
+               .dtb_func  = __soc_builtin_dtb_f__##name,               \
+       }
+
+extern unsigned long __soc_builtin_dtb_table_start;
+extern unsigned long __soc_builtin_dtb_table_end;
+
+void *soc_lookup_builtin_dtb(void);
+
 #endif

diff --git a/arch/riscv/kernel/setup.c b/arch/riscv/kernel/setup.c
index 145128a..3e52831 100644 (file)
--- a/arch/riscv/kernel/setup.c
+++ b/arch/riscv/kernel/setup.c
@@ -75,7 +75,11 @@ void __init setup_arch(char **cmdline_p)
 
        setup_bootmem();
        paging_init();
+#if IS_ENABLED(CONFIG_BUILTIN_DTB)
+       unflatten_and_copy_device_tree();
+#else
        unflatten_device_tree();
+#endif
        clint_init_boot_cpu();
 
 #ifdef CONFIG_SWIOTLB

diff --git a/arch/riscv/kernel/soc.c b/arch/riscv/kernel/soc.c
index 0b3b3dc..1fc8762 100644 (file)
--- 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;
+}

diff --git a/arch/riscv/kernel/vmlinux.lds.S b/arch/riscv/kernel/vmlinux.lds.S
index 0339b6b..e6f8016 100644 (file)
--- a/arch/riscv/kernel/vmlinux.lds.S
+++ b/arch/riscv/kernel/vmlinux.lds.S
@@ -34,6 +34,11 @@ SECTIONS
                KEEP(*(__soc_early_init_table))
                __soc_early_init_table_end = .;
        }
+       __soc_builtin_dtb_table : {
+               __soc_builtin_dtb_table_start = .;
+               KEEP(*(__soc_builtin_dtb_table))
+               __soc_builtin_dtb_table_end = .;
+       }
        /* we have to discard exit text and such at runtime, not link time */
        .exit.text :
        {

diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
index 27a3341..c18b3db 100644 (file)
--- a/arch/riscv/mm/init.c
+++ b/arch/riscv/mm/init.c
@@ -17,6 +17,7 @@
 #include <asm/fixmap.h>
 #include <asm/tlbflush.h>
 #include <asm/sections.h>
+#include <asm/soc.h>
 #include <asm/pgtable.h>
 #include <asm/io.h>
 
@@ -493,7 +494,15 @@ void free_initmem(void)
 #else
 asmlinkage void __init setup_vm(uintptr_t dtb_pa)
 {
+#ifdef CONFIG_BUILTIN_DTB
+       dtb_early_va = soc_lookup_builtin_dtb();
+       if (!dtb_early_va) {
+               /* Fallback to first available DTS */
+               dtb_early_va = (void *) __dtb_start;
+       }
+#else
        dtb_early_va = (void *)dtb_pa;
+#endif
 }
 
 static inline void setup_vm_final(void)