[PATCH] ppc: L2 cache prefetch fixes on 745x

We run into problems if we blindly enable L2 prefetching without
checking that the L2 cache is actually enabled. Additionaly, if we
disable the L2 cache we need to ensure that we disable L2 prefetching.

Signed-off-by: Kumar Gala <[e-mail]>
Signed-off-by: Benjamin Herrenschmidt <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

arch/ppc/kernel/cpu_setup_6xx.S

···
 	sync
 	isync
 
-	/* Enable L2 HW prefetch
+	/* Enable L2 HW prefetch, if L2 is enabled
 	 */
+	mfspr	r3,SPRN_L2CR
+	andis.	r3,r3,L2CR_L2E@h
+	beqlr
 	mfspr	r3,SPRN_MSSCR0
 	ori	r3,r3,3
 	sync

arch/ppc/kernel/l2cr.S

···
 	       The bit moved on the 7450.....
 	  ****/
 
+BEGIN_FTR_SECTION
+	/* Disable L2 prefetch on some 745x and try to ensure
+	 * L2 prefetch engines are idle. As explained by errata
+	 * text, we can't be sure they are, we just hope very hard
+	 * that well be enough (sic !). At least I noticed Apple
+	 * doesn't even bother doing the dcbf's here...
+	 */
+	mfspr	r4,SPRN_MSSCR0
+	rlwinm	r4,r4,0,0,29
+	sync
+	mtspr	SPRN_MSSCR0,r4
+	sync
+	isync
+	lis	r4,KERNELBASE@h
+	dcbf	0,r4
+	dcbf	0,r4
+	dcbf	0,r4
+	dcbf	0,r4
+END_FTR_SECTION_IFSET(CPU_FTR_SPEC7450)
+
 	/* TODO: use HW flush assist when available */
 
 	lis	r4,0x0002
···
 	oris	r3,r3,0x8000
 	mtspr	SPRN_L2CR,r3
 	sync
-
+	
+	/* Enable L2 HW prefetch on 744x/745x */
+BEGIN_FTR_SECTION
+	mfspr	r3,SPRN_MSSCR0
+	ori	r3,r3,3
+	sync
+	mtspr	SPRN_MSSCR0,r3
+	sync
+	isync
+END_FTR_SECTION_IFSET(CPU_FTR_SPEC7450)
 4:
 
 	/* Restore HID0[DPM] to whatever it was before */