sh: Setup early PMB mappings.

More and more boards are going to start shipping that boot with the MMU
in 32BIT mode by default. Previously we relied on the bootloader to
setup PMB mappings for use by the kernel but we also need to cater for
boards whose bootloaders don't set them up.

If CONFIG_PMB_LEGACY is not enabled we have full control over our PMB
mappings and can compress our address space. Usually, the distance
between the the cached and uncached mappings of RAM is always 512MB,
however we can compress the distance to be the amount of RAM on the
board.

pmb_init() now becomes much simpler. It no longer has to calculate any
mappings, it just has to synchronise the software PMB table with the
hardware.

Tested on SDK7786 and SH7785LCR.

Signed-off-by: Matt Fleming <matt@console-pimps.org>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>

arch/sh/kernel/head_32.S

@@ -3,6 +3,7 @@
  *  arch/sh/kernel/head.S
  *
  *  Copyright (C) 1999, 2000  Niibe Yutaka & Kaz Kojima
+ *  Copyright (C) 2010  Matt Fleming
  *
  * This file is subject to the terms and conditions of the GNU General Public
  * License.  See the file "COPYING" in the main directory of this archive
@@ -84,6 +85,236 @@ ENTRY(_stext)
 	ldc	r0, r7_bank	! ... and initial thread_info
 #endif
 
+#if defined(CONFIG_PMB) && !defined(CONFIG_PMB_LEGACY)
+	/*
+	 * Reconfigure the initial PMB mappings setup by the hardware.
+	 *
+	 * When we boot in 32-bit MMU mode there are 2 PMB entries already
+	 * setup for us.
+	 *
+	 * Entry       VPN	   PPN	    V	SZ	C	UB	WT
+	 * ---------------------------------------------------------------
+	 *   0	    0x80000000 0x00000000   1  512MB	1	0	1
+	 *   1	    0xA0000000 0x00000000   1  512MB	0	0	0
+	 *
+	 * But we reprogram them here because we want complete control over
+	 * our address space and the initial mappings may not map PAGE_OFFSET
+	 * to __MEMORY_START (or even map all of our RAM).
+	 *
+	 * Once we've setup cached and uncached mappings for all of RAM we
+	 * clear the rest of the PMB entries.
+	 *
+	 * This clearing also deals with the fact that PMB entries can persist
+	 * across reboots. The PMB could have been left in any state when the
+	 * reboot occurred, so to be safe we clear all entries and start with
+	 * with a clean slate.
+	 */
+
+	mov.l	.LMMUCR, r1	/* Flush the TLB */
+	mov.l	@r1, r0
+	or	#MMUCR_TI, r0
+	mov.l	r0, @r1
+
+	mov.l	.LMEMORY_SIZE, r5
+	mov	r5, r7
+
+	mov	#PMB_E_SHIFT, r0
+	mov	#0x1, r4
+	shld	r0, r4
+
+	mov.l	.LFIRST_DATA_ENTRY, r0
+	mov.l	.LPMB_DATA, r1
+	mov.l	.LFIRST_ADDR_ENTRY, r2
+	mov.l	.LPMB_ADDR, r3
+
+	mov	#0, r10
+
+	/*
+	 * r0 = PMB_DATA data field
+	 * r1 = PMB_DATA address field
+	 * r2 = PMB_ADDR data field
+	 * r3 = PMB_ADDR address field
+	 * r4 = PMB_E_SHIFT
+	 * r5 = remaining amount of RAM to map
+	 * r6 = PMB mapping size we're trying to use
+	 * r7 = cached_to_uncached
+	 * r8 = scratch register
+	 * r9 = scratch register
+	 * r10 = number of PMB entries we've setup
+	 */
+.L512:
+	mov	#(512 >> 4), r6
+	shll16	r6
+	shll8	r6
+
+	cmp/hi	r5, r6
+	bt	.L128
+
+	mov	#(PMB_SZ_512M >> 2), r9
+	shll2	r9
+
+	/*
+	 * Cached mapping
+	 */
+	mov	#PMB_C, r8
+	or	r0, r8
+	or	r9, r8
+	mov.l	r8, @r1
+	mov.l	r2, @r3
+
+	add	r4, r1		/* Increment to the next PMB_DATA entry */
+	add	r4, r3		/* Increment to the next PMB_ADDR entry */
+
+	add	#1, r10		/* Increment number of PMB entries */
+
+	/*
+	 * Uncached mapping
+	 */
+	mov	#(PMB_UB >> 8), r8
+	shll8	r8
+
+	or	r0, r8
+	or	r9, r8
+	mov.l	r8, @r1
+	mov	r2, r8
+	add	r7, r8
+	mov.l	r8, @r3
+
+	add	r4, r1		/* Increment to the next PMB_DATA entry */
+	add	r4, r3		/* Increment to the next PMB_ADDR entry */
+
+	add	#1, r10		/* Increment number of PMB entries */
+
+	sub	r6, r5
+	add	r6, r0
+	add	r6, r2
+
+	bra	.L512
+
+.L128:
+	mov	#(128 >> 4), r6
+	shll16	r6
+	shll8	r6
+
+	cmp/hi	r5, r6
+	bt	.L64
+
+	mov	#(PMB_SZ_128M >> 2), r9
+	shll2	r9
+
+	/*
+	 * Cached mapping
+	 */
+	mov	#PMB_C, r8
+	or	r0, r8
+	or	r9, r8
+	mov.l	r8, @r1
+	mov.l	r2, @r3
+
+	add	r4, r1		/* Increment to the next PMB_DATA entry */
+	add	r4, r3		/* Increment to the next PMB_ADDR entry */
+
+	add	#1, r10		/* Increment number of PMB entries */
+
+	/*
+	 * Uncached mapping
+	 */
+	mov	#(PMB_UB >> 8), r8
+	shll8	r8
+
+	or	r0, r8
+	or	r9, r8
+	mov.l	r8, @r1
+	mov	r2, r8
+	add	r7, r8
+	mov.l	r8, @r3
+
+	add	r4, r1		/* Increment to the next PMB_DATA entry */
+	add	r4, r3		/* Increment to the next PMB_ADDR entry */
+
+	add	#1, r10		/* Increment number of PMB entries */
+
+	sub	r6, r5
+	add	r6, r0
+	add	r6, r2
+
+	bra	.L128
+
+.L64:
+	mov	#(64 >> 4), r6
+	shll16	r6
+	shll8	r6
+
+	cmp/hi	r5, r6
+	bt	.Ldone
+
+	mov	#(PMB_SZ_64M >> 2), r9
+	shll2	r9
+
+	/*
+	 * Cached mapping
+	 */
+	mov	#PMB_C, r8
+	or	r0, r8
+	or	r9, r8
+	mov.l	r8, @r1
+	mov.l	r2, @r3
+
+	add	r4, r1		/* Increment to the next PMB_DATA entry */
+	add	r4, r3		/* Increment to the next PMB_ADDR entry */
+
+	add	#1, r10		/* Increment number of PMB entries */
+
+	/*
+	 * Uncached mapping
+	 */
+	mov	#(PMB_UB >> 8), r8
+	shll8	r8
+
+	or	r0, r8
+	or	r9, r8
+	mov.l	r8, @r1
+	mov	r2, r8
+	add	r7, r8
+	mov.l	r8, @r3
+
+	add	r4, r1		/* Increment to the next PMB_DATA entry */
+	add	r4, r3		/* Increment to the next PMB_ADDR entry */
+
+	add	#1, r10		/* Increment number of PMB entries */
+
+	sub	r6, r5
+	add	r6, r0
+	add	r6, r2
+
+	bra	.L64
+
+.Ldone:
+	/* Update cached_to_uncached */
+	mov.l	.Lcached_to_uncached, r0
+	mov.l	r7, @r0
+
+	/*
+	 * Clear the remaining PMB entries.
+	 *
+	 * r3 = entry to begin clearing from
+	 * r10 = number of entries we've setup so far
+	 */
+	mov	#0, r1
+	mov	#PMB_ENTRY_MAX, r0
+
+.Lagain:
+	mov.l	r1, @r3		/* Clear PMB_ADDR entry */
+	add	#1, r10		/* Increment the loop counter */
+	cmp/eq	r0, r10
+	bf/s	.Lagain
+	 add	r4, r3		/* Increment to the next PMB_ADDR entry */
+
+	mov.l	6f, r0
+	icbi	@r0
+
+#endif /* !CONFIG_PMB_LEGACY */
+
 #ifndef CONFIG_SH_NO_BSS_INIT
 	/*
 	 * Don't clear BSS if running on slow platforms such as an RTL simulation,
@@ -133,3 +364,13 @@ ENTRY(stack_start)
 5:	.long	start_kernel
 6:	.long	sh_cpu_init
 7:	.long	init_thread_union
+
+#if defined(CONFIG_PMB) && !defined(CONFIG_PMB_LEGACY)
+.LPMB_ADDR:		.long	PMB_ADDR
+.LPMB_DATA:		.long	PMB_DATA
+.LFIRST_ADDR_ENTRY:	.long	PAGE_OFFSET | PMB_V
+.LFIRST_DATA_ENTRY:	.long	__MEMORY_START | PMB_V
+.LMMUCR:		.long	MMUCR
+.Lcached_to_uncached:	.long	cached_to_uncached
+.LMEMORY_SIZE:		.long	__MEMORY_SIZE
+#endif