s390/mem_detect: replace tprot loop with binary search

In a situation when other memory detection methods are not available
(no SCLP and no z/VM diag260), continuous online memory is assumed.
Replacing tprot loop with faster binary search, as only online memory
end has to be found.

Reviewed-by: Heiko Carstens <[e-mail]>
Reviewed-by: Martin Schwidefsky <[e-mail]>
Signed-off-by: Vasily Gorbik <[e-mail]>
Signed-off-by: Martin Schwidefsky <[e-mail]>

arch/s390/boot/mem_detect.c

···
 #include <asm/sclp.h>
 #include <asm/sections.h>
 #include <asm/mem_detect.h>
+#include <asm/sparsemem.h>
 #include "compressed/decompressor.h"
 #include "boot.h"
-
-#define CHUNK_READ_WRITE 0
-#define CHUNK_READ_ONLY  1
 
 unsigned long __bootdata(max_physmem_end);
 struct mem_detect_info __bootdata(mem_detect);
···
 	return rc;
 }
 
-static void scan_memory(unsigned long rzm)
+static void search_mem_end(void)
 {
-	unsigned long addr, size;
-	int type;
+	unsigned long range = 1 << (MAX_PHYSMEM_BITS - 20); /* in 1MB blocks */
+	unsigned long offset = 0;
+	unsigned long pivot;
 
-	if (!rzm)
-		rzm = 1UL << 20;
+	while (range > 1) {
+		range >>= 1;
+		pivot = offset + range;
+		if (!tprot(pivot << 20))
+			offset = pivot;
+	}
 
-	addr = 0;
-	do {
-		size = 0;
-		/* assume lowcore is writable */
-		type = addr ? tprot(addr) : CHUNK_READ_WRITE;
-		do {
-			size += rzm;
-			if (max_physmem_end && addr + size >= max_physmem_end)
-				break;
-		} while (type == tprot(addr + size));
-		if (type == CHUNK_READ_WRITE || type == CHUNK_READ_ONLY) {
-			if (max_physmem_end && (addr + size > max_physmem_end))
-				size = max_physmem_end - addr;
-			add_mem_detect_block(addr, addr + size);
-		}
-		addr += size;
-	} while (addr < max_physmem_end);
+	add_mem_detect_block(0, (offset + 1) << 20);
 }
 
 void detect_memory(void)
 {
-	unsigned long rzm;
-
-	sclp_early_get_meminfo(&max_physmem_end, &rzm);
+	sclp_early_get_memsize(&max_physmem_end);
 
 	if (!sclp_early_read_storage_info()) {
 		mem_detect.info_source = MEM_DETECT_SCLP_STOR_INFO;
···
 		return;
 	}
 
-	scan_memory(rzm);
-	mem_detect.info_source = MEM_DETECT_TPROT_LOOP;
+	search_mem_end();
+	mem_detect.info_source = MEM_DETECT_BIN_SEARCH;
 	max_physmem_end = get_mem_detect_end();
 }

arch/s390/include/asm/mem_detect.h

···
 	MEM_DETECT_SCLP_STOR_INFO,
 	MEM_DETECT_DIAG260,
 	MEM_DETECT_SCLP_READ_INFO,
-	MEM_DETECT_TPROT_LOOP
+	MEM_DETECT_BIN_SEARCH
 };
 
 struct mem_detect_block {

arch/s390/include/asm/sclp.h

···
 void sclp_early_printk_force(const char *s);
 void __sclp_early_printk(const char *s, unsigned int len, unsigned int force);
 
-int sclp_early_get_meminfo(unsigned long *mem, unsigned long *rzm);
+int sclp_early_get_memsize(unsigned long *mem);
 int _sclp_get_core_info(struct sclp_core_info *info);
 int sclp_core_configure(u8 core);
 int sclp_core_deconfigure(u8 core);

drivers/s390/char/sclp_early_core.c

···
 	return 0;
 }
 
-int __init sclp_early_get_meminfo(unsigned long *mem, unsigned long *rzm)
+int __init sclp_early_get_memsize(unsigned long *mem)
 {
 	unsigned long rnmax;
 	unsigned long rnsize;
···
 	rnsize = sccb->rnsize ? sccb->rnsize : sccb->rnsize2;
 	rnsize <<= 20;
 	*mem = rnsize * rnmax;
-	*rzm = rnsize;
 	return 0;
 }