powerpc/nohash: Convert set_context() to C

ppc8xx already has set_context() in C.

Other ones have it in assembly. The only thing it does is to
write the context id into SPRN_PID.

Do it in C.
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/a5d0759064f3831c6b88af49ef5d3b05ba1c4dad.1622712515.git.christophe.leroy@csgroup.eu

arch/powerpc/include/asm/mmu_context.h

@@ -57,7 +57,6 @@ static inline bool mm_iommu_is_devmem(struct mm_struct *mm, unsigned long hpa,
 static inline void mm_iommu_init(struct mm_struct *mm) { }
 #endif
 extern void switch_slb(struct task_struct *tsk, struct mm_struct *mm);
-extern void set_context(unsigned long id, pgd_t *pgd);
 
 #ifdef CONFIG_PPC_BOOK3S_64
 extern void radix__switch_mmu_context(struct mm_struct *prev,

arch/powerpc/kernel/head_40x.S

@@ -702,13 +702,6 @@ _GLOBAL(abort)
         oris    r13,r13,DBCR0_RST_SYSTEM@h
         mtspr   SPRN_DBCR0,r13
 
-_GLOBAL(set_context)
-	sync
-	mtspr	SPRN_PID,r3
-	isync				/* Need an isync to flush shadow */
-					/* TLBs after changing PID */
-	blr
-
 /* We put a few things here that have to be page-aligned. This stuff
  * goes at the beginning of the data segment, which is page-aligned.
  */

arch/powerpc/kernel/head_44x.S

@@ -788,11 +788,6 @@ _GLOBAL(__fixup_440A_mcheck)
 	sync
 	blr
 
-_GLOBAL(set_context)
-	mtspr	SPRN_PID,r3
-	isync			/* Force context change */
-	blr
-
 /*
  * Init CPU state. This is called at boot time or for secondary CPUs
  * to setup initial TLB entries, setup IVORs, etc...

arch/powerpc/kernel/head_fsl_booke.S

@@ -985,11 +985,6 @@ _GLOBAL(abort)
 	mtspr	SPRN_DBCR0,r13
 	isync
 
-_GLOBAL(set_context)
-	mtspr	SPRN_PID,r3
-	isync			/* Force context change */
-	blr
-
 #ifdef CONFIG_SMP
 /* When we get here, r24 needs to hold the CPU # */
 	.globl __secondary_start

arch/powerpc/mm/nohash/8xx.c

@@ -212,31 +212,6 @@ void __init setup_initial_memory_limit(phys_addr_t first_memblock_base,
 	memblock_set_current_limit(min_t(u64, first_memblock_size, SZ_32M));
 }
 
-/*
- * 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));
-
-	/* Register M_TWB 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_TWB, __pa(pgd) - offset);
-
-	/* Update context */
-	mtspr(SPRN_M_CASID, id - 1);
-	/* sync */
-	mb();
-}
-
 #ifdef CONFIG_PPC_KUEP
 void __init setup_kuep(bool disabled)
 {

arch/powerpc/mm/nohash/mmu_context.c

@@ -264,6 +264,33 @@ static void context_check_map(void)
 static void context_check_map(void) { }
 #endif
 
+static void set_context(unsigned long id, pgd_t *pgd)
+{
+	if (IS_ENABLED(CONFIG_PPC_8xx)) {
+		s16 offset = (s16)(__pa(swapper_pg_dir));
+
+		/*
+		 * Register M_TWB 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_TWB, __pa(pgd) - offset);
+
+		/* Update context */
+		mtspr(SPRN_M_CASID, id - 1);
+
+		/* sync */
+		mb();
+	} else {
+		if (IS_ENABLED(CONFIG_40x))
+			mb();	/* sync */
+
+		mtspr(SPRN_PID, id);
+		isync();
+	}
+}
+
 void switch_mmu_context(struct mm_struct *prev, struct mm_struct *next,
 			struct task_struct *tsk)
 {

arch/powerpc/mm/nohash/tlb_low.S

@@ -360,11 +360,6 @@ _GLOBAL(_tlbivax_bcast)
 	sync
 	wrtee	r10
 	blr
-
-_GLOBAL(set_context)
-	mtspr	SPRN_PID,r3
-	isync			/* Force context change */
-	blr
 #else
 #error Unsupported processor type !
 #endif