xen/arm: Move the code to map FDT in the boot tables from assembly to C

The FDT will not be accessed before start_xen (begining of C code) is
called and it will be easier to maintain as the code could be common
between AArch32 and AArch64.

A new function early_fdt_map is introduced to map the FDT in the boot
page table.

Signed-off-by: Julien Grall <julien.grall@arm.com>
Reviewed-by: Stefano Stabellini <sstabellini@kernel.org>

xen/arch/arm/arm32/head.S

@@ -389,20 +389,6 @@ paging:
         /* Use a virtual address to access the UART. */
         ldr   r11, =EARLY_UART_VIRTUAL_ADDRESS
 #endif
-        /* Map the DTB in the boot misc slot */
-        teq   r12, #0                /* Only on boot CPU */
-        bne   1f
-
-        ldr   r1, =boot_second
-        mov   r3, #0x0
-        lsr   r2, r8, #SECOND_SHIFT
-        lsl   r2, r2, #SECOND_SHIFT  /* r2: 2MB-aligned paddr of DTB */
-        orr   r2, r2, #PT_UPPER(MEM)
-        orr   r2, r2, #PT_LOWER(MEM) /* r2:r3 := 2MB RAM incl. DTB */
-        ldr   r4, =BOOT_FDT_VIRT_START
-        mov   r4, r4, lsr #(SECOND_SHIFT - 3)   /* Slot for BOOT_FDT_VIRT_START */
-        strd  r2, r3, [r1, r4]       /* Map it in the early fdt slot */
-1:
 
         /*
          * Flush the TLB in case the 1:1 mapping happens to clash with

xen/arch/arm/arm64/head.S

@@ -550,19 +550,6 @@ paging:
         ldr   x23, =EARLY_UART_VIRTUAL_ADDRESS
 #endif
 
-        /* Map the DTB in the boot misc slot */
-        cbnz  x22, 1f                /* Only on boot CPU */
-
-        ldr   x4, =boot_second       /* x4 := vaddr (boot_second) */
-        lsr   x2, x21, #SECOND_SHIFT
-        lsl   x2, x2, #SECOND_SHIFT  /* x2 := 2MB-aligned paddr of DTB */
-        mov   x3, #PT_MEM            /* x2 := 2MB RAM incl. DTB */
-        orr   x2, x2, x3
-        ldr   x1, =BOOT_FDT_VIRT_START
-        lsr   x1, x1, #(SECOND_SHIFT - 3)   /* x4 := Slot for BOOT_FDT_VIRT_START */
-        str   x2, [x4, x1]           /* Map it in the early fdt slot */
-1:
-
         /*
          * Flush the TLB in case the 1:1 mapping happens to clash with
          * the virtual addresses used by the fixmap or DTB.

xen/arch/arm/mm.c

@@ -38,6 +38,7 @@
 #include <xen/vmap.h>
 #include <xsm/xsm.h>
 #include <xen/pfn.h>
+#include <xen/sizes.h>
 
 struct domain *dom_xen, *dom_io, *dom_cow;
 
@@ -468,6 +469,18 @@ static inline lpae_t pte_of_xenaddr(vaddr_t va)
     return mfn_to_xen_entry(mfn, WRITEALLOC);
 }
 
+/* Map the FDT in the early boot page table */
+void * __init early_fdt_map(paddr_t fdt_paddr)
+{
+    /* We are using 2MB superpage for mapping the FDT */
+    paddr_t base_paddr = fdt_paddr & SECOND_MASK;
+
+    create_mappings(boot_second, BOOT_FDT_VIRT_START, paddr_to_pfn(base_paddr),
+                    SZ_2M >> PAGE_SHIFT, SZ_2M);
+
+    return (void *)BOOT_FDT_VIRT_START + (fdt_paddr % SECOND_SIZE);
+}
+
 void __init remove_early_mappings(void)
 {
     lpae_t pte = {0};

xen/arch/arm/setup.c

@@ -724,9 +724,7 @@ void __init start_xen(unsigned long boot_phys_offset,
 
     smp_clear_cpu_maps();
 
-    /* This is mapped by head.S */
-    device_tree_flattened = (void *)BOOT_FDT_VIRT_START
-        + (fdt_paddr & ((1 << SECOND_SHIFT) - 1));
+    device_tree_flattened = early_fdt_map(fdt_paddr);
     fdt_size = boot_fdt_info(device_tree_flattened, fdt_paddr);
 
     cmdline = boot_fdt_cmdline(device_tree_flattened);

xen/include/asm-arm/mm.h

@@ -160,6 +160,8 @@ extern unsigned long total_pages;
 
 /* Boot-time pagetable setup */
 extern void setup_pagetables(unsigned long boot_phys_offset, paddr_t xen_paddr);
+/* Map FDT in boot pagetable */
+extern void *early_fdt_map(paddr_t fdt_paddr);
 /* Remove early mappings */
 extern void remove_early_mappings(void);
 /* Allocate and initialise pagetables for a secondary CPU. Sets init_ttbr to the