openrisc: tlb miss handler optimizations

By slightly reorganizing the code, the number of registers
used in the tlb miss handlers can be reduced by two,
thus removing the need to save them to memory.

Also, some dead and commented out code is removed.

No functional change.
Signed-off-by: Stefan Kristiansson <stefan.kristiansson@saunalahti.fi>
Signed-off-by: Jonas Bonn <jonas@southpole.se>
Signed-off-by: Stafford Horne <shorne@gmail.com>

arch/openrisc/kernel/head.S

@@ -971,8 +971,6 @@ ENTRY(dtlb_miss_handler)
 	EXCEPTION_STORE_GPR2
 	EXCEPTION_STORE_GPR3
 	EXCEPTION_STORE_GPR4
-	EXCEPTION_STORE_GPR5
-	EXCEPTION_STORE_GPR6
 	/*
 	 * get EA of the miss
 	 */
@@ -980,91 +978,70 @@ ENTRY(dtlb_miss_handler)
 	/*
 	 * pmd = (pmd_t *)(current_pgd + pgd_index(daddr));
 	 */
-	GET_CURRENT_PGD(r3,r5)		// r3 is current_pgd, r5 is temp
+	GET_CURRENT_PGD(r3,r4)		// r3 is current_pgd, r4 is temp
 	l.srli	r4,r2,0x18		// >> PAGE_SHIFT + (PAGE_SHIFT - 2)
 	l.slli	r4,r4,0x2		// to get address << 2
-	l.add	r5,r4,r3		// r4 is pgd_index(daddr)
+	l.add	r3,r4,r3		// r4 is pgd_index(daddr)
 	/*
 	 * if (pmd_none(*pmd))
 	 *   goto pmd_none:
 	 */
-	tophys	(r4,r5)
+	tophys	(r4,r3)
 	l.lwz	r3,0x0(r4)		// get *pmd value
 	l.sfne	r3,r0
 	l.bnf	d_pmd_none
-	 l.andi	r3,r3,~PAGE_MASK //0x1fff		// ~PAGE_MASK
-	/*
-	 * if (pmd_bad(*pmd))
-	 *   pmd_clear(pmd)
-	 *   goto pmd_bad:
-	 */
-//	l.sfeq	r3,r0			// check *pmd value
-//	l.bf	d_pmd_good
-	l.addi	r3,r0,0xffffe000	// PAGE_MASK
-//	l.j	d_pmd_bad
-//	l.sw	0x0(r4),r0		// clear pmd
+	 l.addi	r3,r0,0xffffe000	// PAGE_MASK
+
 d_pmd_good:
 	/*
 	 * pte = *pte_offset(pmd, daddr);
 	 */
 	l.lwz	r4,0x0(r4)		// get **pmd value
 	l.and	r4,r4,r3		// & PAGE_MASK
-	l.srli	r5,r2,0xd		// >> PAGE_SHIFT, r2 == EEAR
-	l.andi	r3,r5,0x7ff		// (1UL << PAGE_SHIFT - 2) - 1
+	l.srli	r2,r2,0xd		// >> PAGE_SHIFT, r2 == EEAR
+	l.andi	r3,r2,0x7ff		// (1UL << PAGE_SHIFT - 2) - 1
 	l.slli	r3,r3,0x2		// to get address << 2
 	l.add	r3,r3,r4
-	l.lwz	r2,0x0(r3)		// this is pte at last
+	l.lwz	r3,0x0(r3)		// this is pte at last
 	/*
 	 * if (!pte_present(pte))
 	 */
-	l.andi	r4,r2,0x1
+	l.andi	r4,r3,0x1
 	l.sfne	r4,r0			// is pte present
 	l.bnf	d_pte_not_present
-	l.addi	r3,r0,0xffffe3fa	// PAGE_MASK | DTLB_UP_CONVERT_MASK
+	l.addi	r4,r0,0xffffe3fa	// PAGE_MASK | DTLB_UP_CONVERT_MASK
 	/*
 	 * fill DTLB TR register
 	 */
-	l.and	r4,r2,r3		// apply the mask
+	l.and	r4,r3,r4		// apply the mask
 	// Determine number of DMMU sets
-	l.mfspr r6, r0, SPR_DMMUCFGR
-	l.andi	r6, r6, SPR_DMMUCFGR_NTS
-	l.srli	r6, r6, SPR_DMMUCFGR_NTS_OFF
+	l.mfspr r2, r0, SPR_DMMUCFGR
+	l.andi	r2, r2, SPR_DMMUCFGR_NTS
+	l.srli	r2, r2, SPR_DMMUCFGR_NTS_OFF
 	l.ori	r3, r0, 0x1
-	l.sll	r3, r3, r6 	// r3 = number DMMU sets DMMUCFGR
-	l.addi	r6, r3, -1  	// r6 = nsets mask
-	l.and	r5, r5, r6	// calc offset:	 & (NUM_TLB_ENTRIES-1)
+	l.sll	r3, r3, r2 	// r3 = number DMMU sets DMMUCFGR
+	l.addi	r2, r3, -1  	// r2 = nsets mask
+	l.mfspr	r3, r0, SPR_EEAR_BASE
+	l.srli	r3, r3, 0xd	// >> PAGE_SHIFT
+	l.and	r2, r3, r2	// calc offset:	 & (NUM_TLB_ENTRIES-1)
 	                                                   //NUM_TLB_ENTRIES
-	l.mtspr	r5,r4,SPR_DTLBTR_BASE(0)
+	l.mtspr	r2,r4,SPR_DTLBTR_BASE(0)
 	/*
 	 * fill DTLB MR register
 	 */
-	l.mfspr	r2,r0,SPR_EEAR_BASE
-	l.addi	r3,r0,0xffffe000	// PAGE_MASK
-	l.and	r4,r2,r3		// apply PAGE_MASK to EA (__PHX__ do we really need this?)
-	l.ori	r4,r4,0x1		// set hardware valid bit: DTBL_MR entry
-	l.mtspr	r5,r4,SPR_DTLBMR_BASE(0)
+	l.slli	r3, r3, 0xd		/* << PAGE_SHIFT => EA & PAGE_MASK */
+	l.ori	r4,r3,0x1		// set hardware valid bit: DTBL_MR entry
+	l.mtspr	r2,r4,SPR_DTLBMR_BASE(0)
 
 	EXCEPTION_LOAD_GPR2
 	EXCEPTION_LOAD_GPR3
 	EXCEPTION_LOAD_GPR4
-	EXCEPTION_LOAD_GPR5
-	EXCEPTION_LOAD_GPR6
-	l.rfe
-d_pmd_bad:
-	l.nop	1
-	EXCEPTION_LOAD_GPR2
-	EXCEPTION_LOAD_GPR3
-	EXCEPTION_LOAD_GPR4
-	EXCEPTION_LOAD_GPR5
-	EXCEPTION_LOAD_GPR6
 	l.rfe
 d_pmd_none:
 d_pte_not_present:
 	EXCEPTION_LOAD_GPR2
 	EXCEPTION_LOAD_GPR3
 	EXCEPTION_LOAD_GPR4
-	EXCEPTION_LOAD_GPR5
-	EXCEPTION_LOAD_GPR6
 	EXCEPTION_HANDLE(_dtlb_miss_page_fault_handler)
 
 /* ==============================================[ ITLB miss handler ]=== */
@@ -1072,8 +1049,6 @@ ENTRY(itlb_miss_handler)
 	EXCEPTION_STORE_GPR2
 	EXCEPTION_STORE_GPR3
 	EXCEPTION_STORE_GPR4
-	EXCEPTION_STORE_GPR5
-	EXCEPTION_STORE_GPR6
 	/*
 	 * get EA of the miss
 	 */
@@ -1083,30 +1058,19 @@ ENTRY(itlb_miss_handler)
 	 * pmd = (pmd_t *)(current_pgd + pgd_index(daddr));
 	 *
 	 */
-	GET_CURRENT_PGD(r3,r5)		// r3 is current_pgd, r5 is temp
+	GET_CURRENT_PGD(r3,r4)		// r3 is current_pgd, r5 is temp
 	l.srli	r4,r2,0x18		// >> PAGE_SHIFT + (PAGE_SHIFT - 2)
 	l.slli	r4,r4,0x2		// to get address << 2
-	l.add	r5,r4,r3		// r4 is pgd_index(daddr)
+	l.add	r3,r4,r3		// r4 is pgd_index(daddr)
 	/*
 	 * if (pmd_none(*pmd))
 	 *   goto pmd_none:
 	 */
-	tophys	(r4,r5)
+	tophys	(r4,r3)
 	l.lwz	r3,0x0(r4)		// get *pmd value
 	l.sfne	r3,r0
 	l.bnf	i_pmd_none
-	l.andi	r3,r3,0x1fff		// ~PAGE_MASK
-	/*
-	 * if (pmd_bad(*pmd))
-	 *   pmd_clear(pmd)
-	 *   goto pmd_bad:
-	 */
-
-//	l.sfeq	r3,r0			// check *pmd value
-//	l.bf	i_pmd_good
-	l.addi	r3,r0,0xffffe000	// PAGE_MASK
-//	l.j	i_pmd_bad
-//	l.sw	0x0(r4),r0		// clear pmd
+	 l.addi	r3,r0,0xffffe000	// PAGE_MASK
 
 i_pmd_good:
 	/*
@@ -1115,35 +1079,36 @@ i_pmd_good:
 	 */
 	l.lwz	r4,0x0(r4)		// get **pmd value
 	l.and	r4,r4,r3		// & PAGE_MASK
-	l.srli	r5,r2,0xd		// >> PAGE_SHIFT, r2 == EEAR
-	l.andi	r3,r5,0x7ff		// (1UL << PAGE_SHIFT - 2) - 1
+	l.srli	r2,r2,0xd		// >> PAGE_SHIFT, r2 == EEAR
+	l.andi	r3,r2,0x7ff		// (1UL << PAGE_SHIFT - 2) - 1
 	l.slli	r3,r3,0x2		// to get address << 2
 	l.add	r3,r3,r4
-	l.lwz	r2,0x0(r3)		// this is pte at last
+	l.lwz	r3,0x0(r3)		// this is pte at last
 	/*
 	 * if (!pte_present(pte))
 	 *
 	 */
-	l.andi	r4,r2,0x1
+	l.andi	r4,r3,0x1
 	l.sfne	r4,r0			// is pte present
 	l.bnf	i_pte_not_present
-	l.addi	r3,r0,0xffffe03a	// PAGE_MASK | ITLB_UP_CONVERT_MASK
+	 l.addi	r4,r0,0xffffe03a	// PAGE_MASK | ITLB_UP_CONVERT_MASK
 	/*
 	 * fill ITLB TR register
 	 */
-	l.and	r4,r2,r3		// apply the mask
-	l.andi	r3,r2,0x7c0		// _PAGE_EXEC | _PAGE_SRE | _PAGE_SWE |  _PAGE_URE | _PAGE_UWE
-//	l.andi	r3,r2,0x400		// _PAGE_EXEC
+	l.and	r4,r3,r4		// apply the mask
+	l.andi	r3,r3,0x7c0		// _PAGE_EXEC | _PAGE_SRE | _PAGE_SWE |  _PAGE_URE | _PAGE_UWE
 	l.sfeq	r3,r0
 	l.bf	itlb_tr_fill //_workaround
 	// Determine number of IMMU sets
-	l.mfspr r6, r0, SPR_IMMUCFGR
-	l.andi	r6, r6, SPR_IMMUCFGR_NTS
-	l.srli	r6, r6, SPR_IMMUCFGR_NTS_OFF
+	l.mfspr r2, r0, SPR_IMMUCFGR
+	l.andi	r2, r2, SPR_IMMUCFGR_NTS
+	l.srli	r2, r2, SPR_IMMUCFGR_NTS_OFF
 	l.ori	r3, r0, 0x1
-	l.sll	r3, r3, r6 	// r3 = number IMMU sets IMMUCFGR
-	l.addi	r6, r3, -1  	// r6 = nsets mask
-	l.and	r5, r5, r6	// calc offset:	 & (NUM_TLB_ENTRIES-1)
+	l.sll	r3, r3, r2 	// r3 = number IMMU sets IMMUCFGR
+	l.addi	r2, r3, -1  	// r2 = nsets mask
+	l.mfspr	r3, r0, SPR_EEAR_BASE
+	l.srli	r3, r3, 0xd	// >> PAGE_SHIFT
+	l.and	r2, r3, r2	// calc offset:	 & (NUM_TLB_ENTRIES-1)
 
 /*
  * __PHX__ :: fixme
@@ -1155,38 +1120,24 @@ i_pmd_good:
 itlb_tr_fill_workaround:
 	l.ori	r4,r4,0xc0		// | (SPR_ITLBTR_UXE | ITLBTR_SXE)
 itlb_tr_fill:
-	l.mtspr	r5,r4,SPR_ITLBTR_BASE(0)
+	l.mtspr	r2,r4,SPR_ITLBTR_BASE(0)
 	/*
 	 * fill DTLB MR register
 	 */
-	l.mfspr	r2,r0,SPR_EEAR_BASE
-	l.addi	r3,r0,0xffffe000	// PAGE_MASK
-	l.and	r4,r2,r3		// apply PAGE_MASK to EA (__PHX__ do we really need this?)
-	l.ori	r4,r4,0x1		// set hardware valid bit: DTBL_MR entry
-	l.mtspr	r5,r4,SPR_ITLBMR_BASE(0)
+	l.slli	r3, r3, 0xd		/* << PAGE_SHIFT => EA & PAGE_MASK */
+	l.ori	r4,r3,0x1		// set hardware valid bit: ITBL_MR entry
+	l.mtspr	r2,r4,SPR_ITLBMR_BASE(0)
 
 	EXCEPTION_LOAD_GPR2
 	EXCEPTION_LOAD_GPR3
 	EXCEPTION_LOAD_GPR4
-	EXCEPTION_LOAD_GPR5
-	EXCEPTION_LOAD_GPR6
 	l.rfe
 
-i_pmd_bad:
-	l.nop	1
-	EXCEPTION_LOAD_GPR2
-	EXCEPTION_LOAD_GPR3
-	EXCEPTION_LOAD_GPR4
-	EXCEPTION_LOAD_GPR5
-	EXCEPTION_LOAD_GPR6
-	l.rfe
 i_pmd_none:
 i_pte_not_present:
 	EXCEPTION_LOAD_GPR2
 	EXCEPTION_LOAD_GPR3
 	EXCEPTION_LOAD_GPR4
-	EXCEPTION_LOAD_GPR5
-	EXCEPTION_LOAD_GPR6
 	EXCEPTION_HANDLE(_itlb_miss_page_fault_handler)
 
 /* ==============================================[ boot tlb handlers ]=== */