arm64: wait for transmit completion before next character transmission

Previous transmission must be completed before next character to be
transmitted, otherwise TX buffer may saturate and we will not see all
the characters on screen.

Signed-off-by: Pratyush Anand <panand@redhat.com>

kexec/arch/arm64/include/arch/options.h

@@ -7,7 +7,8 @@
 #define OPT_PAGE_OFFSET		((OPT_MAX)+3)
 #define OPT_PORT		((OPT_MAX)+4)
 #define OPT_REUSE_CMDLINE	((OPT_MAX)+5)
-#define OPT_ARCH_MAX		((OPT_MAX)+6)
+#define OPT_PORT_LSR		((OPT_MAX)+6)
+#define OPT_ARCH_MAX		((OPT_MAX)+7)
 
 #define KEXEC_ARCH_OPTIONS \
 	KEXEC_OPTIONS \
@@ -17,6 +18,7 @@
 	{ "initrd",       1, NULL, OPT_INITRD }, \
 	{ "page-offset",  1, NULL, OPT_PAGE_OFFSET }, \
 	{ "port",         1, NULL, OPT_PORT }, \
+	{ "port-lsr",     1, NULL, OPT_PORT_LSR }, \
 	{ "ramdisk",      1, NULL, OPT_INITRD }, \
 	{ "reuse-cmdline", 0, NULL, OPT_REUSE_CMDLINE }, \
 
@@ -30,6 +32,7 @@ static const char arm64_opts_usage[] __attribute__ ((unused)) =
 "     --dtb=FILE            Use FILE as the device tree blob.\n"
 "     --initrd=FILE         Use FILE as the kernel initial ramdisk.\n"
 "     --port=ADDRESS        Purgatory output to port ADDRESS.\n"
+"     --port-lsr=ADDR,VAL   Purgatory output port line status address and TX Empty Bit Field.\n"
 "     --ramdisk=FILE        Use FILE as the kernel initial ramdisk.\n"
 "     --reuse-cmdline       Use command line arg of primary kernel.\n";
 
@@ -39,6 +42,8 @@ struct arm64_opts {
 	const char *initrd;
 	uint64_t page_offset;
 	uint64_t port;
+	uint64_t port_lsr;
+	uint32_t port_lsr_val;
 };
 
 extern struct arm64_opts arm64_opts;

kexec/arch/arm64/kexec-arm64.c

@@ -97,6 +97,12 @@ int arch_process_options(int argc, char **argv)
 		case OPT_PORT:
 			arm64_opts.port = strtoull(optarg, NULL, 0);
 			break;
+		case OPT_PORT_LSR:
+			arm64_opts.port_lsr = strtoull(strtok(optarg, ","),
+							NULL, 0);
+			arm64_opts.port_lsr_val = strtoul(strtok(NULL, ","),
+							NULL, 0);
+			break;
 		case OPT_PAGE_OFFSET:
 			arm64_opts.page_offset = strtoull(optarg, NULL, 0);
 			break;
@@ -589,6 +595,8 @@ int arm64_load_other_segments(struct kexec_info *info,
 	uint64_t dtb_base;
 	unsigned long hole_min, hole_max;
 	uint64_t purgatory_sink;
+	uint64_t purgatory_sink_lsr;
+	uint32_t purgatory_sink_lsr_val;
 	struct mem_ehdr ehdr;
 	char *initrd_buf = NULL;
 	struct dtb dtb_1 = {.name = "dtb_1"};
@@ -611,6 +619,9 @@ int arm64_load_other_segments(struct kexec_info *info,
 	dbgprintf("%s:%d: purgatory sink: 0x%" PRIx64 "\n", __func__, __LINE__,
 		purgatory_sink);
 
+	purgatory_sink_lsr = arm64_opts.port_lsr;
+	purgatory_sink_lsr_val = arm64_opts.port_lsr_val;
+
 	if (arm64_opts.dtb) {
 		dtb_2.buf = slurp_file(arm64_opts.dtb, &dtb_2.size);
 		assert(dtb_2.buf);
@@ -707,6 +718,12 @@ int arm64_load_other_segments(struct kexec_info *info,
 	elf_rel_set_symbol(&info->rhdr, "arm64_sink", &purgatory_sink,
 		sizeof(purgatory_sink));
 
+	elf_rel_set_symbol(&info->rhdr, "arm64_sink_lsr", &purgatory_sink_lsr,
+		sizeof(purgatory_sink_lsr));
+
+	elf_rel_set_symbol(&info->rhdr, "arm64_sink_lsr_val",
+		&purgatory_sink_lsr_val, sizeof(purgatory_sink_lsr_val));
+
 	elf_rel_set_symbol(&info->rhdr, "arm64_kernel_entry", &kernel_entry,
 		sizeof(kernel_entry));
 

purgatory/arch/arm64/entry.S

@@ -43,6 +43,11 @@ arm64_sink:
 	.quad	0
 size arm64_sink
 
+.globl arm64_sink_lsr
+arm64_sink_lsr:
+	.quad	0
+size arm64_sink_lsr
+
 .globl arm64_kernel_entry
 arm64_kernel_entry:
 	.quad	0
@@ -57,3 +62,8 @@ size arm64_dtb_addr
 arm64_kexec_lite:
 	.quad	0
 size arm64_kexec_lite
+
+.globl arm64_sink_lsr_val
+arm64_sink_lsr_val:
+	.long	0
+size arm64_sink_lsr_val

purgatory/arch/arm64/purgatory-arm64.c

@@ -8,18 +8,38 @@
 /* Symbols set by kexec. */
 
 extern uint32_t *arm64_sink;
+extern uint32_t *arm64_sink_lsr;
+extern uint32_t arm64_sink_lsr_val;
 extern void (*arm64_kernel_entry)(uint64_t);
 extern uint64_t arm64_dtb_addr;
 
+static void wait_for_xmit_complete(void)
+{
+	volatile uint32_t status;
+	volatile uint32_t *status_reg = (volatile uint32_t *)arm64_sink_lsr;
+
+	if (!arm64_sink_lsr)
+		return;
+
+	while (1) {
+		status = *status_reg;
+		if ((status & arm64_sink_lsr_val) == arm64_sink_lsr_val)
+			break;
+	}
+}
+
 void putchar(int ch)
 {
 	if (!arm64_sink)
 		return;
 
+	wait_for_xmit_complete();
 	*arm64_sink = ch;
 
-	if (ch == '\n')
+	if (ch == '\n') {
+		wait_for_xmit_complete();
 		*arm64_sink = '\r';
+	}
 }
 
 void post_verification_setup_arch(void)