[PATCH] xen/arm/efi: merge neighboring banks

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

When booting from U-Boot bootefi, there can be a high number of
neighboring RAM banks. See for example:

(XEN) RAM: 0000000000000000 - 0000000000bfffff
(XEN) RAM: 0000000000c00000 - 0000000000c00fff
(XEN) RAM: 0000000000c01000 - 0000000000dfffff
(XEN) RAM: 0000000000e00000 - 000000000279dfff
(XEN) RAM: 000000000279e000 - 00000000029fffff
(XEN) RAM: 0000000002a00000 - 0000000008379fff
(XEN) RAM: 000000000837a000 - 00000000083fffff
(XEN) RAM: 0000000008400000 - 0000000008518fff
(XEN) RAM: 0000000008519000 - 00000000085fffff
(XEN) RAM: 0000000008600000 - 0000000008613fff
(XEN) RAM: 0000000008614000 - 00000000097fffff
(XEN) RAM: 0000000009800000 - 00000000098a7fff
(XEN) RAM: 00000000098a8000 - 0000000009dfffff
(XEN) RAM: 0000000009e00000 - 0000000009ea7fff
(XEN) RAM: 0000000009ea8000 - 000000001fffffff
(XEN) RAM: 0000000020000000 - 000000002007ffff
(XEN) RAM: 0000000020080000 - 0000000077b17fff
(XEN) RAM: 0000000077b19000 - 0000000077b2bfff
(XEN) RAM: 0000000077b2c000 - 0000000077c8dfff
(XEN) RAM: 0000000077c8e000 - 0000000077c91fff
(XEN) RAM: 0000000077ca7000 - 0000000077caafff
(XEN) RAM: 0000000077cac000 - 0000000077caefff
(XEN) RAM: 0000000077cd0000 - 0000000077cd2fff
(XEN) RAM: 0000000077cd4000 - 0000000077cd7fff
(XEN) RAM: 0000000077cd8000 - 000000007bd07fff
(XEN) RAM: 000000007bd09000 - 000000007fd5ffff
(XEN) RAM: 000000007fd70000 - 000000007fefffff
(XEN) RAM: 0000000800000000 - 000000087fffffff

It is undesirable to keep them separate, as this approach consumes more
resources.

Additionally, Xen does not currently support boot modules that span
multiple banks: at least one of the regions get freed twice. The first
time from setup_mm->populate_boot_allocator, then again from
discard_initial_modules->fw_unreserved_regions. With a high number of
banks, it can be difficult to arrange the boot modules in a way that
avoids spanning across multiple banks.

This small patch merges neighboring regions, to make dealing with them
more efficient, and to make it easier to load boot modules. The patch
also takes the opportunity to check and discard duplicates.

Signed-off-by: Stefano Stabellini <stefano.stabellini@xxxxxxx>

diff --git a/xen/arch/arm/efi/efi-boot.h b/xen/arch/arm/efi/efi-boot.h
index a80a5a7ab3..f6f23ed5b2 100644
--- a/xen/arch/arm/efi/efi-boot.h
+++ b/xen/arch/arm/efi/efi-boot.h
@@ -163,6 +163,20 @@ static bool __init meminfo_add_bank(struct membanks *mem,
     struct membank *bank;
     paddr_t start = desc->PhysicalStart;
     paddr_t size = desc->NumberOfPages * EFI_PAGE_SIZE;
+    int j;
+
+    for ( j = 0; j < mem->nr_banks; j++ )
+    {
+        if ( mem->bank[j].start == start && mem->bank[j].size == size )
+        {
+            return true;
+        }
+        else if ( mem->bank[j].start + mem->bank[j].size == start )
+        {
+            mem->bank[j].size += size;
+            return true;
+        }
+    }
 
     if ( mem->nr_banks >= mem->max_banks )
         return false;