powerpc/8xx: rewrite set_context() in C

There is no real need to have set_context() in assembly.
Now that we have mtspr() handling CPU6 ERRATA directly, we
can rewrite set_context() in C language for easier maintenance.

Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
Signed-off-by: Scott Wood <oss@buserror.net>

arch/powerpc/kernel/head_8xx.S

@@ -882,50 +882,6 @@ initial_mmu:
 	blr
 
 
-/*
- * Set up to use a given MMU context.
- * r3 is context number, r4 is PGD pointer.
- *
- * We place the physical address of the new task page directory loaded
- * into the MMU base register, and set the ASID compare register with
- * the new "context."
- */
-_GLOBAL(set_context)
-
-#ifdef CONFIG_BDI_SWITCH
-	/* Context switch the PTE pointer for the Abatron BDI2000.
-	 * The PGDIR is passed as second argument.
-	 */
-	lis	r5, KERNELBASE@h
-	lwz	r5, 0xf0(r5)
-	stw	r4, 0x4(r5)
-#endif
-
-	/* Register M_TW will contain base address of level 1 table minus the
-	 * lower part of the kernel PGDIR base address, so that all accesses to
-	 * level 1 table are done relative to lower part of kernel PGDIR base
-	 * address.
-	 */
-	li	r5, (swapper_pg_dir-PAGE_OFFSET)@l
-	sub	r4, r4, r5
-	tophys	(r4, r4)
-#ifdef CONFIG_8xx_CPU6
-	lis	r6, cpu6_errata_word@h
-	ori	r6, r6, cpu6_errata_word@l
-	li	r7, 0x3f80
-	stw	r7, 12(r6)
-	lwz	r7, 12(r6)
-#endif
-	mtspr	SPRN_M_TW, r4		/* Update pointeur to level 1 table */
-#ifdef CONFIG_8xx_CPU6
-	li	r7, 0x3380
-	stw	r7, 12(r6)
-	lwz	r7, 12(r6)
-#endif
-	mtspr	SPRN_M_CASID, r3	/* Update context */
-	SYNC
-	blr
-
 /*
  * We put a few things here that have to be page-aligned.
  * This stuff goes at the beginning of the data segment,

arch/powerpc/mm/8xx_mmu.c

@@ -98,3 +98,37 @@ void setup_initial_memory_limit(phys_addr_t first_memblock_base,
 	memblock_set_current_limit(min_t(u64, first_memblock_size, 0x00800000));
 #endif
 }
+
+/*
+ * Set up to use a given MMU context.
+ * id is context number, pgd is PGD pointer.
+ *
+ * We place the physical address of the new task page directory loaded
+ * into the MMU base register, and set the ASID compare register with
+ * the new "context."
+ */
+void set_context(unsigned long id, pgd_t *pgd)
+{
+	s16 offset = (s16)(__pa(swapper_pg_dir));
+
+#ifdef CONFIG_BDI_SWITCH
+	pgd_t	**ptr = *(pgd_t ***)(KERNELBASE + 0xf0);
+
+	/* Context switch the PTE pointer for the Abatron BDI2000.
+	 * The PGDIR is passed as second argument.
+	 */
+	*(ptr + 1) = pgd;
+#endif
+
+	/* Register M_TW will contain base address of level 1 table minus the
+	 * lower part of the kernel PGDIR base address, so that all accesses to
+	 * level 1 table are done relative to lower part of kernel PGDIR base
+	 * address.
+	 */
+	mtspr(SPRN_M_TW, __pa(pgd) - offset);
+
+	/* Update context */
+	mtspr(SPRN_M_CASID, id);
+	/* sync */
+	mb();
+}