linux-kernel - [PATCH] m68k: Unroll raw

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Date:   Sat, 13 Oct 2018 11:47:55 +1100
From:   Finn Thain <fthain@...egraphics.com.au>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:     linux-m68k@...ts.linux-m68k.org, linux-kernel@...r.kernel.org
Subject: [PATCH] m68k: Unroll raw_outsb() loop

Unroll the raw_outsb() loop using the optimized assembler code from
raw_outsw(). That code is copied and pasted, with movew changed to moveb.

This improves the performance of sequential write transfers using mac_esp
in PIO mode by 5% or 10%. (The DMA controller on the 840av/660av models is
still unsupported so PIO transfers are used.)

Tested-by: Stan Johnson <userm57@...oo.com>
Signed-off-by: Finn Thain <fthain@...egraphics.com.au>
---
In a separate patch series, mac_esp adopts writesb() in place of inline
assembler, making that code smaller and more reusable.
---
 arch/m68k/include/asm/raw_io.h | 39 +++++++++++++++++++++++++++++++++++----
 1 file changed, 35 insertions(+), 4 deletions(-)

diff --git a/arch/m68k/include/asm/raw_io.h b/arch/m68k/include/asm/raw_io.h
index 85761255dde5..8a6dc6e5a279 100644
--- a/arch/m68k/include/asm/raw_io.h
+++ b/arch/m68k/include/asm/raw_io.h
@@ -107,12 +107,43 @@ static inline void raw_insb(volatile u8 __iomem *port, u8 *buf, unsigned int len
 }
 
 static inline void raw_outsb(volatile u8 __iomem *port, const u8 *buf,
-			     unsigned int len)
+			     unsigned int nr)
 {
-	unsigned int i;
+	unsigned int tmp;
 
-        for (i = 0; i < len; i++)
-		out_8(port, *buf++);
+	if (nr & 15) {
+		tmp = (nr & 15) - 1;
+		asm volatile (
+			"1: moveb %0@+,%2@; dbra %1,1b"
+			: "=a" (buf), "=d" (tmp)
+			: "a" (port), "0" (buf),
+			  "1" (tmp));
+	}
+	if (nr >> 4) {
+		tmp = (nr >> 4) - 1;
+		asm volatile (
+			"1: "
+			"moveb %0@+,%2@; "
+			"moveb %0@+,%2@; "
+			"moveb %0@+,%2@; "
+			"moveb %0@+,%2@; "
+			"moveb %0@+,%2@; "
+			"moveb %0@+,%2@; "
+			"moveb %0@+,%2@; "
+			"moveb %0@+,%2@; "
+			"moveb %0@+,%2@; "
+			"moveb %0@+,%2@; "
+			"moveb %0@+,%2@; "
+			"moveb %0@+,%2@; "
+			"moveb %0@+,%2@; "
+			"moveb %0@+,%2@; "
+			"moveb %0@+,%2@; "
+			"moveb %0@+,%2@; "
+			"dbra %1,1b"
+			: "=a" (buf), "=d" (tmp)
+			: "a" (port), "0" (buf),
+			  "1" (tmp));
+	}
 }
 
 static inline void raw_insw(volatile u16 __iomem *port, u16 *buf, unsigned int nr)
-- 
2.16.4