sh: Merge legacy and dynamic PMB modes.

This implements a bit of rework for the PMB code, which permits us to
kill off the legacy PMB mode completely. Rather than trusting the boot
loader to do the right thing, we do a quick verification of the PMB
contents to determine whether to have the kernel setup the initial
mappings or whether it needs to mangle them later on instead.

If we're booting from legacy mappings, the kernel will now take control
of them and make them match the kernel's initial mapping configuration.
This is accomplished by breaking the initialization phase out in to
multiple steps: synchronization, merging, and resizing. With the recent
rework, the synchronization code establishes page links for compound
mappings already, so we build on top of this for promoting mappings and
reclaiming unused slots.

At the same time, the changes introduced for the uncached helpers also
permit us to dynamically resize the uncached mapping without any
particular headaches. The smallest page size is more than sufficient for
mapping all of kernel text, and as we're careful not to jump to any far
off locations in the setup code the mapping can safely be resized
regardless of whether we are executing from it or not.

Signed-off-by: Paul Mundt <lethal@linux-sh.org>

1 files changed, 38 insertions, 4 deletions

diff --git a/arch/sh/kernel/head_32.S b/arch/sh/kernel/head_32.S
index 79ff39517f8e..fe0b743881b0 100644
--- a/arch/sh/kernel/head_32.S
+++ b/arch/sh/kernel/head_32.S
@@ -85,7 +85,7 @@ ENTRY(_stext)
         ldc     r0, r7_bank     ! ... and initial thread_info
 #endif
 
-#if defined(CONFIG_PMB) && !defined(CONFIG_PMB_LEGACY)
+#ifdef CONFIG_PMB
 /*
  * Reconfigure the initial PMB mappings setup by the hardware.
  *
@@ -139,7 +139,6 @@ ENTRY(_stext)
         mov.l   r0, @r1
 
         mov.l   .LMEMORY_SIZE, r5
-        mov     r5, r7
 
         mov     #PMB_E_SHIFT, r0
         mov     #0x1, r4
@@ -150,6 +149,40 @@ ENTRY(_stext)
         mov.l   .LFIRST_ADDR_ENTRY, r2
         mov.l   .LPMB_ADDR, r3
 
+        /*
+         * First we need to walk the PMB and figure out if there are any
+         * existing mappings that match the initial mappings VPN/PPN.
+         * If these have already been established by the bootloader, we
+         * don't bother setting up new entries here, and let the late PMB
+         * initialization take care of things instead.
+         *
+         * Note that we may need to coalesce and merge entries in order
+         * to reclaim more available PMB slots, which is much more than
+         * we want to do at this early stage.
+         */
+        mov     #0, r10
+        mov     #NR_PMB_ENTRIES, r9
+
+        mov     r1, r7          /* temporary PMB_DATA iter */
+
+.Lvalidate_existing_mappings:
+
+        mov.l   @r7, r8
+        and     r0, r8
+        cmp/eq  r0, r8          /* Check for valid __MEMORY_START mappings */
+        bt      .Lpmb_done
+
+        add     #1, r10         /* Increment the loop counter */
+        cmp/eq  r9, r10
+        bf/s    .Lvalidate_existing_mappings
+         add    r4, r7          /* Increment to the next PMB_DATA entry */
+
+        /*
+         * If we've fallen through, continue with setting up the initial
+         * mappings.
+         */
+
+        mov     r5, r7          /* cached_to_uncached */
         mov     #0, r10
 
 #ifdef CONFIG_UNCACHED_MAPPING
@@ -252,7 +285,8 @@ ENTRY(_stext)
         mov.l   6f, r0
         icbi    @r0
 
-#endif /* !CONFIG_PMB_LEGACY */
+.Lpmb_done:
+#endif /* CONFIG_PMB */
 
 #ifndef CONFIG_SH_NO_BSS_INIT
         /*
@@ -304,7 +338,7 @@ ENTRY(stack_start)
 6:      .long   sh_cpu_init
 7:      .long   init_thread_union
 
-#if defined(CONFIG_PMB) && !defined(CONFIG_PMB_LEGACY)
+#ifdef CONFIG_PMB
 .LPMB_ADDR:             .long   PMB_ADDR
 .LPMB_DATA:             .long   PMB_DATA
 .LFIRST_ADDR_ENTRY:     .long   PAGE_OFFSET | PMB_V