tashaboot: arm64 bringup, semihosting payload loader

consoles on the pl011 the dtb points at, walks the memory node and
chosen, loads an arm64 kernel Image over semihosting and jumps to it
with the documented register state. string functions, printf and
libfdt are vendored from lk (lk2nd) and u-boot so the libc surface is
the one those projects already proved. built and booted on qemu virt,
payload exits clean through semihosting.

1 files changed, 191 insertions, 0 deletions

diff --git a/common/console.c b/common/console.c
new file mode 100644
index 0000000..2e9bfa6
--- /dev/null
+++ b/common/console.c
@@ -0,0 +1,191 @@
+/*
+ * console.c - the console dprintf writes to. the dtb picks the uart,
+ * chosen/stdout-path first, any arm,pl011 node as fallback.
+ *
+ * Copyright (c) 2008 Travis Geiselbrecht
+ * Copyright (c) 2026 Bradley Morgan <brads@mainlining.org>
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining
+ * a copy of this software and associated documentation files
+ * (the "Software"), to deal in the Software without restriction,
+ * including without limitation the rights to use, copy, modify, merge,
+ * publish, distribute, sublicense, and/or sell copies of the Software,
+ * and to permit persons to whom the Software is furnished to do so,
+ * subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be
+ * included in all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+ * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+ * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
+ * IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
+ * CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
+ * TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
+ * SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+ */
+
+#include <string.h>
+#include <stdio.h>
+#include <stdarg.h>
+#include <sys/types.h>
+#include <stdint.h>
+#include <libfdt.h>
+#include <printf.h>
+#include <debug.h>
+#include <reg.h>
+#include <drivers/serial/pl011.h>
+
+static uintptr_t tb_uart_base;
+static uint32 tb_uart_clock;
+static bool tb_uart_ready;
+
+/*
+ * read one reg pair out of a node. cells are u32s in the blob, address
+ * and size widths come from the parent #address-cells/#size-cells,
+ * 2/1 is what every board we care about uses, qemu virt included.
+ */
+static int tb_read_reg(const void *blob, int node, int index,
+		       uintptr_t *base, uint32 *size)
+{
+	const fdt32_t *prop;
+	int len;
+	int offset;
+
+	prop = fdt_getprop(blob, node, "reg", &len);
+	if (!prop)
+		return -1;
+
+	/*
+	 * a reg pair here is <addr_hi addr_lo size>, 3 cells, 2 for the
+	 * address and 1 for the size. index 0 is the pair we want.
+	 */
+	offset = index * 3;
+	if (offset + 3 > len / 4)
+		return -1;
+
+	*base = ((uintptr_t)fdt32_to_cpu(prop[offset]) << 32) |
+		fdt32_to_cpu(prop[offset + 1]);
+	*size = fdt32_to_cpu(prop[offset + 2]);
+	return 0;
+}
+
+static int tb_console_from_stdout_path(const void *blob)
+{
+	const char *path;
+	const char *p;
+	char buf[32];
+	int node;
+	int chosen;
+	int len;
+
+	chosen = fdt_path_offset(blob, "/chosen");
+	if (chosen < 0)
+		return -1;
+
+	path = fdt_getprop(blob, chosen, "stdout-path", &len);
+	if (!path || len <= 0)
+		return -1;
+
+	/* the path can carry :baud after the node, cut it */
+	p = strchr(path, ':');
+	len = p ? (int)(p - path) : strlen(path);
+	if (len >= (int)sizeof(buf))
+		len = sizeof(buf) - 1;
+	memcpy(buf, path, len);
+	buf[len] = 0;
+
+	/* a leading / is a full path, otherwise it's an alias */
+	if (buf[0] == '/')
+		node = fdt_path_offset(blob, buf);
+	else
+		node = fdt_path_offset(blob, fdt_get_alias(blob, buf));
+	if (node < 0)
+		return -1;
+
+	return node;
+}
+
+static int tb_console_scan(const void *blob)
+{
+	const char *compat;
+	int node;
+	int len;
+
+	fdt_for_each_subnode(node, blob, 0) {
+		compat = fdt_getprop(blob, node, "compatible", &len);
+		if (!compat)
+			continue;
+		if (fdt_stringlist_contains(compat, len, "arm,pl011"))
+			return node;
+	}
+	return -1;
+}
+
+int tb_console_init(const void *dtb)
+{
+	const fdt32_t *clk;
+	int node;
+	uint32 size;
+	uint32 baud;
+	int len;
+
+	node = tb_console_from_stdout_path(dtb);
+	if (node < 0)
+		node = tb_console_scan(dtb);
+	if (node < 0)
+		return -1;
+
+	if (tb_read_reg(dtb, node, 0, &tb_uart_base, &size))
+		return -1;
+
+	clk = fdt_getprop(dtb, node, "clock-frequency", &len);
+	tb_uart_clock = (clk && len == 4) ? fdt32_to_cpu(*clk) : 24000000;
+
+	{
+		const fdt32_t *cs;
+		int cslen;
+
+		cs = fdt_getprop(dtb, node, "current-speed", &cslen);
+		baud = (cs && cslen == 4) ? fdt32_to_cpu(*cs) : 115200;
+	}
+
+	pl011_init(tb_uart_base, tb_uart_clock, baud);
+	tb_uart_ready = true;
+	return 0;
+}
+
+static int tb_console_out(char c, void *state)
+{
+	if (c == '\n')
+		pl011_putc(tb_uart_base, '\r');
+	pl011_putc(tb_uart_base, c);
+	return 1;
+}
+
+int _dprintf(const char *fmt, ...)
+{
+	va_list ap;
+	int ret;
+
+	if (!tb_uart_ready)
+		return 0;
+
+	va_start(ap, fmt);
+	ret = _dvprintf(fmt, ap);
+	va_end(ap);
+	return ret;
+}
+
+int _dvprintf(const char *fmt, va_list ap)
+{
+	if (!tb_uart_ready)
+		return 0;
+	return _printf_engine(tb_console_out, NULL, fmt, ap);
+}
+
+void platform_halt(void)
+{
+	for (;;)
+		__asm__ volatile("wfe");
+}