linux-kernel - [PATCH 3.12 21/39] m68k/mac: Make SCC reset work more reliably

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Date:	Mon, 25 Jan 2016 12:50:02 +0100
From:	Jiri Slaby <jslaby@...e.cz>
To:	stable@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org,
	Finn Thain <fthain@...egraphics.com.au>,
	Geert Uytterhoeven <geert@...ux-m68k.org>,
	Oliver Neukum <ONeukum@...e.com>, Jiri Slaby <jslaby@...e.cz>
Subject: [PATCH 3.12 21/39] m68k/mac: Make SCC reset work more reliably

From: Finn Thain <fthain@...egraphics.com.au>

3.12-stable review patch.  If anyone has any objections, please let me know.

===============

commit 56931d73697c99ecf7aba6ae86c94d3a2d15d596 upstream.

For SCC initialization we cannot assume that the control register is in
the correct state to accept a register pointer. So first read from the
control register in order to "sync" up.

Signed-off-by: Finn Thain <fthain@...egraphics.com.au>
Signed-off-by: Geert Uytterhoeven <geert@...ux-m68k.org>
Cc: Oliver Neukum <ONeukum@...e.com>
Signed-off-by: Jiri Slaby <jslaby@...e.cz>
---
 arch/m68k/kernel/head.S | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/arch/m68k/kernel/head.S b/arch/m68k/kernel/head.S
index ac85f16534af..4180f8b20374 100644
--- a/arch/m68k/kernel/head.S
+++ b/arch/m68k/kernel/head.S
@@ -2909,7 +2909,9 @@ func_start	serial_init,%d0/%d1/%a0/%a1
 
 #if defined(MAC_USE_SCC_A) || defined(MAC_USE_SCC_B)
 	movel	%pc@(L(mac_sccbase)),%a0
-	/* Reset SCC device */
+	/* Reset SCC register pointer */
+	moveb	%a0@(mac_scc_cha_a_ctrl_offset),%d0
+	/* Reset SCC device: write register pointer then register value */
 	moveb	#9,%a0@(mac_scc_cha_a_ctrl_offset)
 	moveb	#0xc0,%a0@(mac_scc_cha_a_ctrl_offset)
 	/* Wait for 5 PCLK cycles, which is about 68 CPU cycles */
-- 
2.7.0