microblaze: Handle TLB skip size dynamically

This patch fix the problem with rootfs on JFFS2 with early printk
console turned on.

The origin version used TLB63 for temporary early printk mapping.
The code expect that kernel is not able to use all 64 TLB entries
till early printk console is remapped by ioremap. After that
temporary mapping on TLB63 is silently lost.
This expectation give the opportunity to have early console pretty
early.

Microblaze systems with JFFS2 rootfs with early printk console turned on
used more than 64 TLB entries before kernel can remap early console.
Based on that kernel does access to bad area because early printk mapping
is rewritten.

This patch introduces tlb_skip variable which dynamically stores number
of skipped TLB entries from the TLB0. skip_tlb=2 means that TLB0 and TLB1
should be skipped.

MICROBLAZE_TLB_SKIP defines how many TLB is skipped at the kernel start.
They can be used for user purpose.

TLB 63 is used for temporary LMB mapping (MICROBLAZE_LMB_TLB_ID).

Also clean TLBLO when kernel starts.

For specific kernel sizes kernel can use just one TLB. Detect this case
and use the second TLB for general purpose.

Change _tlbia function to flush TLB entries from tlb_skip to TLB_SIZE.

Export tlb_skip size through debugfs.

Signed-off-by: Michal Simek <monstr@monstr.eu>

1 files changed, 27 insertions, 15 deletions

diff --git a/arch/microblaze/kernel/head.S b/arch/microblaze/kernel/head.S
index 49dd48f9e6ec..98b17f9f904b 100644
--- a/arch/microblaze/kernel/head.S
+++ b/arch/microblaze/kernel/head.S
@@ -149,6 +149,7 @@ _copy_bram:
 _invalidate:
 	mts	rtlbx, r3
 	mts	rtlbhi, r0			/* flush: ensure V is clear   */
+	mts	rtlblo, r0
 	bgtid	r3, _invalidate		/* loop for all entries       */
 	addik	r3, r3, -1
 	/* sync */
@@ -224,8 +225,14 @@ tlb_end:
 	andi	r4,r4,0xfffffc00	/* Mask off the real page number */
 	ori	r4,r4,(TLB_WR | TLB_EX)	/* Set the write and execute bits */
 
-	/* TLB0 can be zeroes that's why we not setup it */
-	beqi	r9, jump_over
+	/*
+	 * TLB0 is always used - check if is not zero (r9 stores TLB0 value)
+	 * if is use TLB1 value and clear it (r10 stores TLB1 value)
+	 */
+	bnei	r9, tlb0_not_zero
+	add	r9, r10, r0
+	add	r10, r0, r0
+tlb0_not_zero:
 
 	/* look at the code below */
 	ori	r30, r0, 0x200
@@ -239,18 +246,21 @@ tlb_end:
 	bneid	r29, 1f
 	addik	r30, r30, 0x80
 1:
-	ori r11, r30, 0
-
 	andi	r3,r3,0xfffffc00	/* Mask off the effective page number */
 	ori	r3,r3,(TLB_VALID)
-	or	r3, r3, r11
+	or	r3, r3, r30
 
-	mts     rtlbx,r0		/* TLB slow 0 */
+	/* Load tlb_skip size value which is index to first unused TLB entry */
+	lwi	r11, r0, TOPHYS(tlb_skip)
+	mts     rtlbx,r11		/* TLB slow 0 */
 
 	mts	rtlblo,r4		/* Load the data portion of the entry */
 	mts	rtlbhi,r3		/* Load the tag portion of the entry */
 
-jump_over:
+	/* Increase tlb_skip size */
+	addik	r11, r11, 1
+	swi	r11, r0, TOPHYS(tlb_skip)
+
 	/* TLB1 can be zeroes that's why we not setup it */
 	beqi	r10, jump_over2
 
@@ -266,27 +276,30 @@ jump_over:
 	bneid	r29, 1f
 	addik	r30, r30, 0x80
 1:
-	ori r12, r30, 0
-
 	addk	r4, r4, r9	/* previous addr + TLB0 size */
 	addk	r3, r3, r9
 
 	andi	r3,r3,0xfffffc00	/* Mask off the effective page number */
 	ori	r3,r3,(TLB_VALID)
-	or	r3, r3, r12
+	or	r3, r3, r30
 
-	ori	r6,r0,1			/* TLB slot 1 */
-	mts     rtlbx,r6
+	lwi	r11, r0, TOPHYS(tlb_skip)
+	mts     rtlbx, r11		/* r11 is used from TLB0 */
 
 	mts	rtlblo,r4		/* Load the data portion of the entry */
 	mts	rtlbhi,r3		/* Load the tag portion of the entry */
 
+	/* Increase tlb_skip size */
+	addik	r11, r11, 1
+	swi	r11, r0, TOPHYS(tlb_skip)
+
 jump_over2:
 	/*
 	 * Load a TLB entry for LMB, since we need access to
 	 * the exception vectors, using a 4k real==virtual mapping.
 	 */
-	ori	r6,r0,3			/* TLB slot 3 */
+	/* Use temporary TLB_ID for LMB - clear this temporary mapping later */
+	ori	r6, r0, MICROBLAZE_LMB_TLB_ID
 	mts     rtlbx,r6
 
 	ori	r4,r0,(TLB_WR | TLB_EX)
@@ -355,8 +368,7 @@ start_here:
 
 	/* Load up the kernel context */
 kernel_load_context:
-	# Keep entry 0 and 1 valid. Entry 3 mapped to LMB can go away.
-	ori	r5,r0,3
+	ori	r5, r0, MICROBLAZE_LMB_TLB_ID
 	mts     rtlbx,r5
 	nop
 	mts	rtlbhi,r0