h2: capture boot registers and forward a DTB address to the Linux guest

kernel/init/boot/boot.h

@@ -50,4 +50,12 @@
 #define SBIT_SIZE 1
 #endif
 
+#if !defined(ASM) && !defined(__ASSEMBLER__)
+/*
+ * Boot parameter block in the entry page (see boot.ref.S): r1:0 as
+ * captured at reset on the boot thread, followed by reserved pad.
+ */
+extern unsigned int h2_boot_params[];
+#endif
+
 #endif

kernel/init/boot/boot.ref.S

@@ -70,10 +70,48 @@
 #define CORE_DONE 0x1
 
 FUNC_START start .entry .p2align 12
+	/*
+	 * STANDALONE test links pull this object in solely for
+	 * h2_boot_params (referenced by info.ref.c) and supply their own
+	 * `start' via crt0_standalone.o.  Weak lets that definition win
+	 * instead of colliding; real (non-STANDALONE) links still resolve
+	 * to this one, since it's the only definition present there.
+	 */
+	.weak start
 	jump .Lpast_mbox
 	.space 0x200  // FIXME: needs to be enough for all angel mailboxes but still fit all code in 4K
 
+	/*
+	 * Boot parameter block: lives at a fixed offset in the entry page
+	 * so that boot firmware or external tooling can locate and patch
+	 * it.  The first two words capture r1:0 as they were at reset on
+	 * the boot thread; bootloaders pass the device tree blob physical
+	 * address there for forwarding to a guest.  The remaining pad is
+	 * reserved for future parameters or a patched-in platform-specific
+	 * boot stub.
+	 */
+	.p2align 3
+	.globl h2_boot_params
+h2_boot_params:
+	.word 0		// r0 at entry (e.g. DTB physical address, low)
+	.word 0		// r1 at entry (e.g. DTB physical address, high)
+	.space 0x38	// reserved
+
 .Lpast_mbox:
+	/*
+	 * Capture r1:0 into the boot parameter block before anything
+	 * clobbers them.  Only the boot thread's values are meaningful;
+	 * secondary hardware threads also enter here when started later.
+	 */
+	r10 = HTID
+	{
+		p0 = cmp.eq(r10,#0)
+		if (!p0.new) jump:nt .Lpast_bootparam_capture
+	}
+	r10 = add(PC,##h2_boot_params@PCREL)
+	memd(r10+#0) = r1:0
+	dccleana(r10)	// reach memory before the cache kill below
+.Lpast_bootparam_capture:
 
 #ifdef CRASH_DEBUG
 	r7 = PC

kernel/traps/info/info.ref.c

@@ -11,6 +11,7 @@
 #include <symbols.h>
 #include <cfg_table.h>
 #include <log.h>
+#include <boot.h>
 
 u32_t H2K_trap_info(info_type op, u32_t unit, h2_cfg_unit_entry entry, H2K_thread_context *me) {
 
@@ -195,7 +196,13 @@ u32_t H2K_trap_info(info_type op, u32_t unit, h2_cfg_unit_entry entry, H2K_threa
 
 	case INFO_NOC_SBASE:
 	return H2K_gp->noc_sbase;
-
+
+	case INFO_BOOT_R00:
+		return h2_boot_params[0];
+
+	case INFO_BOOT_R01:
+		return h2_boot_params[1];
+
 default:
 		return -1;
 	}

libs/h2/common/h2_common_info.h

@@ -53,6 +53,8 @@ typedef enum {
 	INFO_TCM_OFFSET,  /**< Multicore TCM base offset */
 	INFO_NOC_MBASE,   /**< Multicore NOC master widget base */
 	INFO_NOC_SBASE,   /**< Multicore NOC slave widget base */
+	INFO_BOOT_R00,    /**< r0 at reset on the boot thread (e.g. DTB address, low) */
+	INFO_BOOT_R01,    /**< r1 at reset on the boot thread (e.g. DTB address, high) */
 	INFO_MAX
 } info_type;
 

linux/loadlinux.c

@@ -145,6 +145,27 @@ void boot_ucos() {
 #endif
 }
 
+/*
+ * The platform bootloader may have passed a device tree blob address in
+ * r1:0 at reset; h2 captures those registers in its entry page.  Return
+ * the DTB physical address if one was passed and looks valid, else 0.
+ */
+static unsigned long boot_dtb_addr(void) {
+
+	unsigned long r0 = h2_info(INFO_BOOT_R00);
+	unsigned long r1 = h2_info(INFO_BOOT_R01);
+
+	if (r1 != 0 || r0 == 0 || (r0 & 3) != 0)
+		return 0;
+
+	if (*(volatile unsigned long *)r0 != 0xedfe0dd0) { /* FDT magic, LE view */
+		PRINTF("linux: no FDT magic at 0x%08lx\n", r0);
+		return 0;
+	}
+
+	return r0;
+}
+
 unsigned long boot_linux(char fname[]) {
 
 	unsigned long linux_vm = 0;
@@ -198,8 +219,11 @@ unsigned long boot_linux(char fname[]) {
 		 );
 #endif
 
+	unsigned long dtb = boot_dtb_addr();
+	PRINTF("linux: dtb at 0x%08lx\n", dtb);
+
 	if (h2_vmboot(linux_stext, &linux_vcpu_stacks[0][VCPU_STACK_SIZE - 1],
-								0, LINUX_VM_PRIO, linux_vm) == -1) FAIL("linux vmboot");
+								dtb, LINUX_VM_PRIO, linux_vm) == -1) FAIL("linux vmboot");
 
 	PRINTF ("linux: booted\n");
 #endif