From fc60d1ebadfba9a4344969507d8bd9de43c5c7e8 Mon Sep 17 00:00:00 2001
Message-Id: <fc60d1ebadfba9a4344969507d8bd9de43c5c7e8.1431592766.git.panand@redhat.com>
In-Reply-To: <1fb6841aa15407dbf371589d7abca7bc2d35815c.1431592766.git.panand@redhat.com>
References: <1fb6841aa15407dbf371589d7abca7bc2d35815c.1431592766.git.panand@redhat.com>
From: Pratyush Anand <panand@redhat.com>
Date: Thu, 16 Apr 2015 14:00:03 +0530
Subject: [PATCH 15/17] 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>
---
 purgatory/arch/arm64/purgatory-arm64.c | 24 +++++++++++++++++++++++-
 1 file changed, 23 insertions(+), 1 deletion(-)

diff --git a/purgatory/arch/arm64/purgatory-arm64.c b/purgatory/arch/arm64/purgatory-arm64.c
index 25960c30bd05..3a1c9243bfa2 100644
--- a/purgatory/arch/arm64/purgatory-arm64.c
+++ b/purgatory/arch/arm64/purgatory-arm64.c
@@ -11,15 +11,37 @@ extern uint32_t *arm64_sink;
 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;
+
+	/*
+	 * Since most of the UART with ARM platform has LSR register at
+	 * offset 0x14 and should have value as 0x60 for TX empty, so we
+	 * have hardcoded these values. Can modify in future if need
+	 * arises.
+	 */
+	status_reg = (volatile uint32_t *)((uint64_t)arm64_sink + 0x14);
+	while (1) {
+		status = *status_reg;
+		if ((status & 0x60) == 0x60)
+			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