arm: Add support for semihosting for armv8 fastmodel targets.

The armv8 ARM Trusted Firmware (ATF) can be used to load various ATF
images and u-boot, and does this for virtual platforms by using
semihosting. This commit extends this idea by allowing u-boot to also
use semihosting to load the kernel/ramdisk/dtb. This eliminates the need
for a bootwrapper and produces a more realistic boot sequence with
virtual models.

Though the semihosting code is quite generic, support for armv7 in
fastmodel is less useful due to the wide range of available silicon
and the lack of a free armv7 fastmodel, so this change contains an
untested armv7 placeholder for the service trap opcode.

Please refer to doc/README.semihosting for a more detailed description
of semihosting and how it is used with the armv8 virtual platforms.

Signed-off-by: Darwin Rambo <drambo@broadcom.com>
Cc: trini@ti.com
Cc: fenghua@phytium.com.cn
Cc: bhupesh.sharma@freescale.com

2 files changed, 234 insertions, 0 deletions

diff --git a/arch/arm/lib/Makefile b/arch/arm/lib/Makefile
index 585f1f7..1ef2400 100644
--- a/arch/arm/lib/Makefile
+++ b/arch/arm/lib/Makefile
@@ -32,6 +32,7 @@ obj-$(CONFIG_USE_ARCH_MEMCPY) += memcpy.o
 else
 obj-$(CONFIG_SPL_FRAMEWORK) += spl.o
 endif
+obj-$(CONFIG_SEMIHOSTING) += semihosting.o
 
 obj-y	+= sections.o
 ifdef CONFIG_ARM64
diff --git a/arch/arm/lib/semihosting.c b/arch/arm/lib/semihosting.c
new file mode 100644
index 0000000..cb5dc26
--- /dev/null
+++ b/arch/arm/lib/semihosting.c
@@ -0,0 +1,233 @@
+/*
+ * Copyright 2014 Broadcom Corporation
+ *
+ * SPDX-License-Identifier:	GPL-2.0+
+ */
+
+/*
+ * Minimal semihosting implementation for reading files into memory. If more
+ * features like writing files or console output are required they can be
+ * added later. This code has been tested on arm64/aarch64 fastmodel only.
+ * An untested placeholder exists for armv7 architectures, but since they
+ * are commonly available in silicon now, fastmodel usage makes less sense
+ * for them.
+ */
+#include <common.h>
+#include <asm/semihosting.h>
+
+#define SYSOPEN		0x01
+#define SYSCLOSE	0x02
+#define SYSREAD		0x06
+#define SYSFLEN		0x0C
+
+#define MODE_READ	0x0
+#define MODE_READBIN	0x1
+
+/*
+ * Call the handler
+ */
+static int smh_trap(unsigned int sysnum, void *addr)
+{
+	register int result asm("r0");
+#if defined(CONFIG_ARM64)
+	asm volatile ("hlt #0xf000" : "=r" (result) : "0"(sysnum), "r"(addr));
+#else
+	/* Note - untested placeholder */
+	asm volatile ("svc #0x123456" : "=r" (result) : "0"(sysnum), "r"(addr));
+#endif
+	return result;
+}
+
+/*
+ * Open, load a file into memory, and close it. Check that the available space
+ * is sufficient to store the entire file. Return the bytes actually read from
+ * the file as seen by the read function. The verbose flag enables some extra
+ * printing of successful read status.
+ */
+int smh_load(const char *fname, void *memp, int avail, int verbose)
+{
+	int ret, fd, len;
+
+	ret = -1;
+
+	debug("%s: fname \'%s\', avail %u, memp %p\n", __func__, fname,
+	      avail, memp);
+
+	/* Open the file */
+	fd = smh_open(fname, "rb");
+	if (fd == -1)
+		return ret;
+
+	/* Get the file length */
+	ret = smh_len_fd(fd);
+	if (ret == -1) {
+		smh_close(fd);
+		return ret;
+	}
+
+	/* Check that the file will fit in the supplied buffer */
+	if (ret > avail) {
+		printf("%s: ERROR ret %d, avail %u\n", __func__, ret,
+		       avail);
+		smh_close(fd);
+		return ret;
+	}
+
+	len = ret;
+
+	/* Read the file into the buffer */
+	ret = smh_read(fd, memp, len);
+	if (ret == 0) {
+		/* Print successful load information if requested */
+		if (verbose) {
+			printf("\n%s\n", fname);
+			printf("    0x%8p dest\n", memp);
+			printf("    0x%08x size\n", len);
+			printf("    0x%08x avail\n", avail);
+		}
+	}
+
+	/* Close the file */
+	smh_close(fd);
+
+	return ret;
+}
+
+/*
+ * Read 'len' bytes of file into 'memp'. Returns 0 on success, else failure
+ */
+int smh_read(int fd, void *memp, int len)
+{
+	int ret;
+	struct smh_read_s {
+		int fd;
+		void *memp;
+		int len;
+	} read;
+
+	debug("%s: fd %d, memp %p, len %d\n", __func__, fd, memp, len);
+
+	read.fd = fd;
+	read.memp = memp;
+	read.len = len;
+
+	ret = smh_trap(SYSREAD, &read);
+	if (ret == 0) {
+		return 0;
+	} else {
+		/*
+		 * The ARM handler allows for returning partial lengths,
+		 * but in practice this never happens so rather than create
+		 * hard to maintain partial read loops and such, just fail
+		 * with an error message.
+		 */
+		printf("%s: ERROR ret %d, fd %d, len %u memp %p\n",
+		       __func__, ret, fd, len, memp);
+	}
+	return ret;
+}
+
+/*
+ * Open a file on the host. Mode is "r" or "rb" currently. Returns a file
+ * descriptor or -1 on error.
+ */
+int smh_open(const char *fname, char *modestr)
+{
+	int ret, fd, mode;
+	struct smh_open_s {
+		const char *fname;
+		unsigned int mode;
+		unsigned int len;
+	} open;
+
+	debug("%s: file \'%s\', mode \'%s\'\n", __func__, fname, modestr);
+
+	ret = -1;
+
+	/* Check the file mode */
+	if (!(strcmp(modestr, "r"))) {
+		mode = MODE_READ;
+	} else if (!(strcmp(modestr, "rb"))) {
+		mode = MODE_READBIN;
+	} else {
+		printf("%s: ERROR mode \'%s\' not supported\n", __func__,
+		       modestr);
+		return ret;
+	}
+
+	open.fname = fname;
+	open.len = strlen(fname);
+	open.mode = mode;
+
+	/* Open the file on the host */
+	fd = smh_trap(SYSOPEN, &open);
+	if (fd == -1)
+		printf("%s: ERROR fd %d for file \'%s\'\n", __func__, fd,
+		       fname);
+
+	return fd;
+}
+
+/*
+ * Close the file using the file descriptor
+ */
+int smh_close(int fd)
+{
+	int ret;
+	long fdlong;
+
+	debug("%s: fd %d\n", __func__, fd);
+
+	fdlong = (long)fd;
+	ret = smh_trap(SYSCLOSE, &fdlong);
+	if (ret == -1)
+		printf("%s: ERROR fd %d\n", __func__, fd);
+
+	return ret;
+}
+
+/*
+ * Get the file length from the file descriptor
+ */
+int smh_len_fd(int fd)
+{
+	int ret;
+	long fdlong;
+
+	debug("%s: fd %d\n", __func__, fd);
+
+	fdlong = (long)fd;
+	ret = smh_trap(SYSFLEN, &fdlong);
+	if (ret == -1)
+		printf("%s: ERROR ret %d\n", __func__, ret);
+
+	return ret;
+}
+
+/*
+ * Get the file length from the filename
+ */
+int smh_len(const char *fname)
+{
+	int ret, fd, len;
+
+	debug("%s: file \'%s\'\n", __func__, fname);
+
+	/* Open the file */
+	fd = smh_open(fname, "rb");
+	if (fd == -1)
+		return fd;
+
+	/* Get the file length */
+	len = smh_len_fd(fd);
+
+	/* Close the file */
+	ret = smh_close(fd);
+	if (ret == -1)
+		return ret;
+
+	debug("%s: returning len %d\n", __func__, len);
+
+	/* Return the file length (or -1 error indication) */
+	return len;
+}