linux-kernel - [PATCH 03/13] openrisc: Add support for liteuart emergency printing

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Message-Id: <20220515124158.3167452-4-shorne@gmail.com>
Date:   Sun, 15 May 2022 21:41:48 +0900
From:   Stafford Horne <shorne@...il.com>
To:     LKML <linux-kernel@...r.kernel.org>
Cc:     Openrisc <openrisc@...ts.librecores.org>,
        Stafford Horne <shorne@...il.com>,
        Jonas Bonn <jonas@...thpole.se>,
        Stefan Kristiansson <stefan.kristiansson@...nalahti.fi>,
        Randy Dunlap <rdunlap@...radead.org>
Subject: [PATCH 03/13] openrisc: Add support for liteuart emergency printing

This patch adds support for sending emergency print output, such as
unhandled exception details, to a liteuart serial device.  This is the
default device available on litex platforms.

If a developer want to use this they should update UART_BASE_ADD
to the address of liteuart.

Signed-off-by: Stafford Horne <shorne@...il.com>
---
 arch/openrisc/kernel/head.S | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/arch/openrisc/kernel/head.S b/arch/openrisc/kernel/head.S
index b1f3a65c271c..21db50563f97 100644
--- a/arch/openrisc/kernel/head.S
+++ b/arch/openrisc/kernel/head.S
@@ -1555,6 +1555,17 @@ ENTRY(_emergency_putc)
 	l.movhi r4,hi(UART_BASE_ADD)
 	l.ori	r4,r4,lo(UART_BASE_ADD)
 
+#if defined(CONFIG_SERIAL_LITEUART)
+	/* Check OFF_TXFULL status */
+1:      l.lwz	r5,4(r4)
+	l.andi	r5,r5,0xff
+	l.sfnei	r5,0
+	l.bf	1b
+	 l.nop
+
+	/* Write character */
+	l.andi	r7,r7,0xff
+	l.sw	0(r4),r7
 #elif defined(CONFIG_SERIAL_8250)
 	/* Check UART LSR THRE (hold) bit */
 	l.addi  r6,r0,0x20
-- 
2.31.1