[PATCH RFC 6/6] arm64: wait for transmit completion before next character transmission

[Pratyush Anand <panand@redhat.com>]

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 | 10 +++++++++-
 kexec/arch/arm64/kexec-arm64.c          | 17 +++++++++++++++++
 purgatory/arch/arm64/entry.S            | 10 ++++++++++
 purgatory/arch/arm64/purgatory-arm64.c  | 22 +++++++++++++++++++++-
 4 files changed, 57 insertions(+), 2 deletions(-)

diff --git a/kexec/arch/arm64/include/arch/options.h b/kexec/arch/arm64/include/arch/options.h
index af14102220ea..a1f6f2cb00be 100644
--- a/kexec/arch/arm64/include/arch/options.h
+++ b/kexec/arch/arm64/include/arch/options.h
@@ -8,7 +8,9 @@
 #define OPT_PAGE_OFFSET	((OPT_MAX)+4)
 #define OPT_PORT	((OPT_MAX)+5)
 #define OPT_REUSE_CMDLINE	((OPT_MAX+6))
-#define OPT_ARCH_MAX	((OPT_MAX)+7)
+#define OPT_PORT_LSR	((OPT_MAX)+7)
+#define OPT_PORT_LSR_VAL	((OPT_MAX)+8)
+#define OPT_ARCH_MAX	((OPT_MAX)+9)
 
 #define KEXEC_ARCH_OPTIONS \
 	KEXEC_OPTIONS \
@@ -19,6 +21,8 @@
 	{ "lite",         0, NULL, OPT_LITE }, \
 	{ "page-offset",  1, NULL, OPT_PAGE_OFFSET }, \
 	{ "port",         1, NULL, OPT_PORT }, \
+	{ "port-lsr",     1, NULL, OPT_PORT_LSR }, \
+	{ "port-lsr-val", 1, NULL, OPT_PORT_LSR_VAL }, \
 	{ "ramdisk",      1, NULL, OPT_INITRD }, \
 	{ "reuse-cmdline", 0, NULL, OPT_REUSE_CMDLINE }, \
 
@@ -34,6 +38,8 @@ static const char arm64_opts_usage[] __attribute__ ((unused)) =
 "     --lite                Fast reboot, no memory integrity checks.\n"
 "     --page-offset         Kernel page-offset for binary image load.\n"
 "     --port=ADDRESS        Purgatory output to port ADDRESS.\n"
+"     --port-lsr=ADDRESS    Purgatory output port line status ADDRESS.\n"
+"     --port-lsr-val=VALUE  Purgatory output port Line status expected SET value when TX empty.\n"
 "     --ramdisk=FILE        Use FILE as the kernel initial ramdisk.\n"
 "     --reuse-cmdline       Use command line arg of primary kernel.\n";
 
@@ -43,6 +49,8 @@ struct arm64_opts {
 	const char *initrd;
 	uint64_t page_offset;
 	uint64_t port;
+	uint64_t port_lsr;
+	uint32_t port_lsr_val;
 	int lite;
 };
 
diff --git a/kexec/arch/arm64/kexec-arm64.c b/kexec/arch/arm64/kexec-arm64.c
index 190037c75186..5c7445b86305 100644
--- a/kexec/arch/arm64/kexec-arm64.c
+++ b/kexec/arch/arm64/kexec-arm64.c
@@ -99,6 +99,12 @@ 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(optarg, NULL, 0);
+			break;
+		case OPT_PORT_LSR_VAL:
+			arm64_opts.port_lsr_val = strtoull(optarg, NULL, 0);
+			break;
 		case OPT_PAGE_OFFSET:
 			arm64_opts.page_offset = strtoull(optarg, NULL, 0);
 			break;
@@ -594,6 +600,8 @@ int arm64_load_other_segments(struct kexec_info *info,
 	unsigned long dtb_base;
 	char *initrd_buf = NULL;
 	uint64_t purgatory_sink;
+	uint64_t purgatory_sink_lsr;
+	uint32_t purgatory_sink_lsr_val;
 	unsigned long purgatory_base;
 	struct dtb dtb_1 = {.name = "dtb_1"};
 	struct dtb dtb_2 = {.name = "dtb_2"};
@@ -615,6 +623,9 @@ 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);
@@ -732,6 +743,12 @@ 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));
 
diff --git a/purgatory/arch/arm64/entry.S b/purgatory/arch/arm64/entry.S
index 140e91d87ab1..fdb2fca774e7 100644
--- a/purgatory/arch/arm64/entry.S
+++ b/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
@@ -52,3 +57,8 @@ size arm64_kernel_entry
 arm64_dtb_addr:
 	.quad	0
 size arm64_dtb_addr
+
+.globl arm64_sink_lsr_val
+arm64_sink_lsr_val:
+	.word	0
+size arm64_sink_lsr_val
diff --git a/purgatory/arch/arm64/purgatory-arm64.c b/purgatory/arch/arm64/purgatory-arm64.c
index 25960c30bd05..1b88bb799f54 100644
--- a/purgatory/arch/arm64/purgatory-arm64.c
+++ b/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 setup_arch(void)
-- 
2.1.0


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