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awilliam
GitHub Repository: awilliam/linux-vfio
 Path: blob/master/arch/sh/lib64/copy_page.S
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/*

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   Copyright 2003 Richard Curnow, SuperH (UK) Ltd.

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   This file is subject to the terms and conditions of the GNU General Public

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   License.  See the file "COPYING" in the main directory of this archive

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   for more details.

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   Tight version of mempy for the case of just copying a page.

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   Prefetch strategy empirically optimised against RTL simulations

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   of SH5-101 cut2 eval chip with Cayman board DDR memory.

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   Parameters:

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   r2 : destination effective address (start of page)

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   r3 : source effective address (start of page)

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   Always copies 4096 bytes.

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   Points to review.

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   * Currently the prefetch is 4 lines ahead and the alloco is 2 lines ahead.

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     It seems like the prefetch needs to be at at least 4 lines ahead to get

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     the data into the cache in time, and the allocos contend with outstanding

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     prefetches for the same cache set, so it's better to have the numbers

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     different.

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   */

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	.section .text..SHmedia32,"ax"

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	.little

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	.balign 8

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	.global copy_page

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copy_page:

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	/* Copy 4096 bytes worth of data from r3 to r2.

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	   Do prefetches 4 lines ahead.

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	   Do alloco 2 lines ahead */

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	pta 1f, tr1

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	pta 2f, tr2

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	pta 3f, tr3

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	ptabs r18, tr0

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#if 0

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	/* TAKum03020 */

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	ld.q r3, 0x00, r63

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	ld.q r3, 0x20, r63

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	ld.q r3, 0x40, r63

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	ld.q r3, 0x60, r63

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#endif

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	alloco r2, 0x00

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	synco		! TAKum03020

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	alloco r2, 0x20

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	synco		! TAKum03020

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	movi 3968, r6

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	add  r2, r6, r6

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	addi r6, 64, r7

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	addi r7, 64, r8

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	sub r3, r2, r60

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	addi r60, 8, r61

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	addi r61, 8, r62

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	addi r62, 8, r23

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	addi r60, 0x80, r22

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/* Minimal code size.  The extra branches inside the loop don't cost much

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   because they overlap with the time spent waiting for prefetches to

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   complete. */

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1:

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#if 0

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	/* TAKum03020 */

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	bge/u r2, r6, tr2  ! skip prefetch for last 4 lines

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	ldx.q r2, r22, r63 ! prefetch 4 lines hence

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#endif

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2:

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	bge/u r2, r7, tr3  ! skip alloco for last 2 lines

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	alloco r2, 0x40    ! alloc destination line 2 lines ahead

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	synco		! TAKum03020

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3:

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	ldx.q r2, r60, r36

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	ldx.q r2, r61, r37

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	ldx.q r2, r62, r38

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	ldx.q r2, r23, r39

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	st.q  r2,   0, r36

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	st.q  r2,   8, r37

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	st.q  r2,  16, r38

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	st.q  r2,  24, r39

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	addi r2, 32, r2

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	bgt/l r8, r2, tr1

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	blink tr0, r63	   ! return

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