ARC: mm: use SCRATCH_DATA0 register for caching pgdir in ARCv2 only

MMU SCRATCH_DATA0 register is intended to cache task pgd. However in
ARC700 SMP port, it has to be repurposed for re-entrant interrupt
handling, while UP port doesn't. We currently handle these use-cases
using a fabricated #define which has usual issues of dependency nesting
and obvious ugliness.

So clean this up: for ARC700 don't use to cache pgd (even in UP) and do
the opposite for ARCv2.

And while here, switch to canonical pgd_offset().
Acked-by: Mike Rapoport <rppt@linux.ibm.com>
Signed-off-by: Vineet Gupta <vgupta@kernel.org>

arch/arc/include/asm/entry-compact.h

@@ -126,19 +126,11 @@
  * to be saved again on kernel mode stack, as part of pt_regs.
  *-------------------------------------------------------------*/
 .macro PROLOG_FREEUP_REG	reg, mem
-#ifndef ARC_USE_SCRATCH_REG
-	sr  \reg, [ARC_REG_SCRATCH_DATA0]
-#else
 	st  \reg, [\mem]
-#endif
 .endm
 
 .macro PROLOG_RESTORE_REG	reg, mem
-#ifndef ARC_USE_SCRATCH_REG
-	lr  \reg, [ARC_REG_SCRATCH_DATA0]
-#else
 	ld  \reg, [\mem]
-#endif
 .endm
 
 /*--------------------------------------------------------------

arch/arc/include/asm/mmu.h

@@ -31,10 +31,6 @@
 #define ARC_REG_SCRATCH_DATA0	0x46c
 #endif
 
-#if defined(CONFIG_ISA_ARCV2) || !defined(CONFIG_SMP)
-#define	ARC_USE_SCRATCH_REG
-#endif
-
 /* Bits in MMU PID register */
 #define __TLB_ENABLE		(1 << 31)
 #define __PROG_ENABLE		(1 << 30)

arch/arc/include/asm/mmu_context.h

@@ -146,7 +146,7 @@ static inline void switch_mm(struct mm_struct *prev, struct mm_struct *next,
 	 */
 	cpumask_set_cpu(cpu, mm_cpumask(next));
 
-#ifdef ARC_USE_SCRATCH_REG
+#ifdef CONFIG_ISA_ARCV2
 	/* PGD cached in MMU reg to avoid 3 mem lookups: task->mm->pgd */
 	write_aux_reg(ARC_REG_SCRATCH_DATA0, next->pgd);
 #endif

arch/arc/include/asm/pgtable.h

@@ -284,29 +284,6 @@ static inline void set_pte_at(struct mm_struct *mm, unsigned long addr,
 	set_pte(ptep, pteval);
 }
 
-/*
- * Macro to quickly access the PGD entry, utlising the fact that some
- * arch may cache the pointer to Page Directory of "current" task
- * in a MMU register
- *
- * Thus task->mm->pgd (3 pointer dereferences, cache misses etc simply
- * becomes read a register
- *
- * ********CAUTION*******:
- * Kernel code might be dealing with some mm_struct of NON "current"
- * Thus use this macro only when you are certain that "current" is current
- * e.g. when dealing with signal frame setup code etc
- */
-#ifdef ARC_USE_SCRATCH_REG
-#define pgd_offset_fast(mm, addr)	\
-({					\
-	pgd_t *pgd_base = (pgd_t *) read_aux_reg(ARC_REG_SCRATCH_DATA0);  \
-	pgd_base + pgd_index(addr);	\
-})
-#else
-#define pgd_offset_fast(mm, addr)	pgd_offset(mm, addr)
-#endif
-
 extern pgd_t swapper_pg_dir[] __aligned(PAGE_SIZE);
 void update_mmu_cache(struct vm_area_struct *vma, unsigned long address,
 		      pte_t *ptep);

arch/arc/mm/fault.c

@@ -33,7 +33,7 @@ noinline static int handle_kernel_vaddr_fault(unsigned long address)
 	pud_t *pud, *pud_k;
 	pmd_t *pmd, *pmd_k;
 
-	pgd = pgd_offset_fast(current->active_mm, address);
+	pgd = pgd_offset(current->active_mm, address);
 	pgd_k = pgd_offset_k(address);
 
 	if (!pgd_present(*pgd_k))

arch/arc/mm/tlb.c

@@ -719,8 +719,8 @@ void arc_mmu_init(void)
 	/* Enable the MMU */
 	write_aux_reg(ARC_REG_PID, MMU_ENABLE);
 
-	/* In smp we use this reg for interrupt 1 scratch */
-#ifdef ARC_USE_SCRATCH_REG
+	/* In arc700/smp needed for re-entrant interrupt handling */
+#ifdef CONFIG_ISA_ARCV2
 	/* swapper_pg_dir is the pgd for the kernel, used by vmalloc */
 	write_aux_reg(ARC_REG_SCRATCH_DATA0, swapper_pg_dir);
 #endif

arch/arc/mm/tlbex.S

@@ -202,7 +202,7 @@ ex_saved_reg1:
 
 	lr  r2, [efa]
 
-#ifdef ARC_USE_SCRATCH_REG
+#ifdef CONFIG_ISA_ARCV2
 	lr  r1, [ARC_REG_SCRATCH_DATA0] ; current pgd
 #else
 	GET_CURR_TASK_ON_CPU  r1