MIPS: OCTEON: use the free memory below the kernel

plat_mem_setup() asks bootmem only for memory above _end. The kernel is loaded at 0x1100000, so whatever bootmem has free below _text is never added to memblock. On a CN6335 board with the Cavium bootloader that is 14MB, 0x200000-0xffffff:

before: node 0: [mem 0x0000000001100000-0x0000000001cc6fff]
after: node 0: [mem 0x0000000000200000-0x0000000000ffffff]

          node 0: [mem 0x0000000001100000-0x0000000001cc6fff]

Claim it before the main loop, in 1MB pieces since the holes there are small and unaligned. It counts towards max_memory like the rest, and a piece inside the crash kernel range, which is added on its own, is skipped as the main loop does. bootmem never hands out what the bootloader reserved (the exception vectors, its named blocks, the kernel image itself), so only free memory is claimed.

---
Tested on mips-next with cavium_octeon_defconfig (KEXEC=y, CRASH_DUMP=n) on a CN6335 board, 4GB, Cavium U-Boot 1.1.1: "Memory:" goes from 4023588K/4169492K to 4037924K/4183828K available. Built with KEXEC=n and CRASH_DUMP=y as well.

 arch/mips/cavium-octeon/setup.c | 21 +++++++++++++++++++++
 1 file changed, 21 insertions(+)

index 7497be7b9431..2b1bc8fafac5 100644
@@ -1022,6 +1022,27 @@ void __init plat_mem_setup(void)
 	 * which is handled by memblock
 	 */
 	cvmx_bootmem_lock();
+	/*
+	 * The loop below only takes memory above the kernel. Claim what
+	 * bootmem has free below it as well, 1MB at a time: the holes the
+	 * bootloader leaves there are small and not aligned to
+	 * mem_alloc_size.
+	 */
+	while (total < max_memory) {
+		memory = cvmx_bootmem_phy_alloc(0x100000, 0,
+						__pa_symbol(&_text),
+						0x100000,
+						CVMX_BOOTMEM_FLAG_NO_LOCKING);
+		if (memory < 0)
+			break;
+#ifdef CONFIG_KEXEC
+		/* The crash kernel range is already added */
+		if (memory < crashk_end && memory + 0x100000 > crashk_base)
+			continue;
+#endif
+		memblock_add(memory, 0x100000);
+		total += 0x100000;
+	}
 	while (total < max_memory) {
 		memory = cvmx_bootmem_phy_alloc(mem_alloc_size,
 						__pa_symbol(&_end), -1,

2.53.0