From: Brad Peters <bpeters@redhat.com>
Date: Fri, 8 Aug 2008 11:03:52 -0400
Subject: [ppc] adds DSCR support in sysfs
Message-id: 489C6058.1010405@redhat.com
O-Subject: Re: [PATCH RHEL5.3] Adds DSCR support in sysfs (the ability to disable data prefetching)
Bugzilla: 439567
RH-Acked-by: David Howells <dhowells@redhat.com>

RHBZ#:
======
https://bugzilla.redhat.com/show_bug.cgi?id=439567

Description:
===========
New Feature / Power arch only

This patch adds DSCR (Debug Status and Control Register) support. This adds
the ability to turn off data prefetching from HW.
It boosts specJBB by 10.7% on P6.

kABI Status:
============
No symbols were harmed.

Brew:
=====
Built on all platforms.
http://brewweb.devel.redhat.com/brew/taskinfo?taskID=1412286

Upstream Status:
================
http://patchwork.ozlabs.org/linuxppc/patch?id=8536
Test Status:
============
Confirmed new controls exist:
> pwd
/sys/devices/system/cpu
[root@ibm-eclipz-nfsserv cpu]# find | grep dscr
./cpu3/dscr
./cpu2/dscr
./cpu1/dscr
./cpu0/dscr

Brad Peters 8-1-08

Proposed Patch:
===============
This patch is based on 2.6.18-99.el5

diff --git a/arch/powerpc/kernel/sysfs.c b/arch/powerpc/kernel/sysfs.c
index 0edb176..86a3b0b 100644
--- a/arch/powerpc/kernel/sysfs.c
+++ b/arch/powerpc/kernel/sysfs.c
@@ -182,6 +182,7 @@ SYSFS_PMCSETUP(pmc7, SPRN_PMC7);
 SYSFS_PMCSETUP(pmc8, SPRN_PMC8);
 SYSFS_PMCSETUP(purr, SPRN_PURR);
 SYSFS_PMCSETUP(spurr, SPRN_SPURR);
+SYSFS_PMCSETUP(dscr, SPRN_DSCR);
 
 static SYSDEV_ATTR(mmcr0, 0600, show_mmcr0, store_mmcr0);
 static SYSDEV_ATTR(mmcr1, 0600, show_mmcr1, store_mmcr1);
@@ -196,6 +197,7 @@ static SYSDEV_ATTR(pmc7, 0600, show_pmc7, store_pmc7);
 static SYSDEV_ATTR(pmc8, 0600, show_pmc8, store_pmc8);
 static SYSDEV_ATTR(purr, 0600, show_purr, NULL);
 static SYSDEV_ATTR(spurr, 0600, show_spurr, NULL);
+static SYSDEV_ATTR(dscr, 0600, show_dscr, store_dscr);
 
 static void register_cpu_online(unsigned int cpu)
 {
@@ -236,6 +238,8 @@ static void register_cpu_online(unsigned int cpu)
 		sysdev_create_file(s, &attr_purr);
 	if (cpu_has_feature(CPU_FTR_SPURR))
 		sysdev_create_file(s, &attr_spurr);
+	if (cpu_has_feature(CPU_FTR_DSCR))
+		sysdev_create_file(s, &attr_dscr);
 }
 
 #ifdef CONFIG_HOTPLUG_CPU
@@ -280,6 +284,8 @@ static void unregister_cpu_online(unsigned int cpu)
 		sysdev_remove_file(s, &attr_purr);
 	if (cpu_has_feature(CPU_FTR_SPURR))
 		sysdev_remove_file(s, &attr_spurr);
+	if (cpu_has_feature(CPU_FTR_DSCR))
+		sysdev_remove_file(s, &attr_dscr);
 }
 #endif /* CONFIG_HOTPLUG_CPU */
 
diff --git a/include/asm-powerpc/cputable.h b/include/asm-powerpc/cputable.h
index ba105f6..d34313c 100644
--- a/include/asm-powerpc/cputable.h
+++ b/include/asm-powerpc/cputable.h
@@ -151,6 +151,7 @@ extern void do_feature_fixups(unsigned long value, void *fixup_start,
 #define CPU_FTR_PURR			LONG_ASM_CONST(0x0000400000000000)
 #define CPU_FTR_CELL_TB_BUG		LONG_ASM_CONST(0x0000800000000000)
 #define CPU_FTR_SPURR			LONG_ASM_CONST(0x0001000000000000)
+#define CPU_FTR_DSCR			LONG_ASM_CONST(0x0002000000000000)
 
 #ifndef __ASSEMBLY__
 
@@ -334,7 +335,7 @@ extern void do_feature_fixups(unsigned long value, void *fixup_start,
 	    CPU_FTR_HPTE_TABLE | CPU_FTR_PPCAS_ARCH_V2 | \
 	    CPU_FTR_MMCRA | CPU_FTR_SMT | \
 	    CPU_FTR_COHERENT_ICACHE | CPU_FTR_LOCKLESS_TLBIE | \
-	    CPU_FTR_PURR | CPU_FTR_REAL_LE | CPU_FTR_SPURR)
+	    CPU_FTR_PURR | CPU_FTR_REAL_LE | CPU_FTR_SPURR | CPU_FTR_DSCR)
 #define CPU_FTRS_CELL	(CPU_FTR_SPLIT_ID_CACHE | CPU_FTR_USE_TB | \
 	    CPU_FTR_HPTE_TABLE | CPU_FTR_PPCAS_ARCH_V2 | \
 	    CPU_FTR_ALTIVEC_COMP | CPU_FTR_MMCRA | CPU_FTR_SMT | \
diff --git a/include/asm-powerpc/reg.h b/include/asm-powerpc/reg.h
index bf86471..da93319 100644
--- a/include/asm-powerpc/reg.h
+++ b/include/asm-powerpc/reg.h
@@ -143,6 +143,7 @@
 
 /* Special Purpose Registers (SPRNs)*/
 #define SPRN_CTR	0x009	/* Count Register */
+#define SPRN_DSCR	0x011	/* Data Stream Control Register */
 #define SPRN_CTRLF	0x088
 #define SPRN_CTRLT	0x098
 #define   CTRL_CT	0xc0000000	/* current thread */