s390/checksum: provide and use cksm() inline assembly

Convert those callers of csum_partial() to use the cksm instruction,
which are either very early or in critical paths, like panic/dump, so
they don't have to rely on a working kernel infrastructure, which will
be introduced with a subsequent patch.

Signed-off-by: Heiko Carstens <[e-mail]>

arch/s390/include/asm/checksum.h

···
 #include <linux/instrumented.h>
 #include <linux/in6.h>
 
+static inline __wsum cksm(const void *buff, int len, __wsum sum)
+{
+	union register_pair rp = {
+		.even = (unsigned long)buff,
+		.odd = (unsigned long)len,
+	};
+
+	instrument_read(buff, len);
+	asm volatile("\n"
+		"0:	cksm	%[sum],%[rp]\n"
+		"	jo	0b\n"
+		: [sum] "+&d" (sum), [rp] "+&d" (rp.pair) : : "cc", "memory");
+	return sum;
+}
+
 /*
  * Computes the checksum of a memory block at buff, length len,
  * and adds in "sum" (32-bit).
···
  */
 static inline __wsum csum_partial(const void *buff, int len, __wsum sum)
 {
-	union register_pair rp = {
-		.even = (unsigned long) buff,
-		.odd = (unsigned long) len,
-	};
-
-	instrument_read(buff, len);
-	asm volatile(
-		"0:	cksm	%[sum],%[rp]\n"
-		"	jo	0b\n"
-		: [sum] "+&d" (sum), [rp] "+&d" (rp.pair) : : "cc", "memory");
-	return sum;
+	return cksm(buff, len, sum);
 }
 
 /*

arch/s390/kernel/ipl.c

···
 	    reipl_type == IPL_TYPE_UNKNOWN)
 		os_info_flags |= OS_INFO_FLAG_REIPL_CLEAR;
 	os_info_entry_add(OS_INFO_FLAGS_ENTRY, &os_info_flags, sizeof(os_info_flags));
-	csum = (__force unsigned int)
-	       csum_partial(reipl_block_actual, reipl_block_actual->hdr.len, 0);
+	csum = (__force unsigned int)cksm(reipl_block_actual, reipl_block_actual->hdr.len, 0);
 	abs_lc = get_abs_lowcore();
 	abs_lc->ipib = __pa(reipl_block_actual);
 	abs_lc->ipib_checksum = csum;

arch/s390/kernel/os_info.c

···
 u32 os_info_csum(struct os_info *os_info)
 {
 	int size = sizeof(*os_info) - offsetof(struct os_info, version_major);
-	return (__force u32)csum_partial(&os_info->version_major, size, 0);
+	return (__force u32)cksm(&os_info->version_major, size, 0);
 }
 
 /*
···
 {
 	os_info.entry[nr].addr = __pa(ptr);
 	os_info.entry[nr].size = size;
-	os_info.entry[nr].csum = (__force u32)csum_partial(ptr, size, 0);
+	os_info.entry[nr].csum = (__force u32)cksm(ptr, size, 0);
 	os_info.csum = os_info_csum(&os_info);
 }
 
···
 		msg = "copy failed";
 		goto fail_free;
 	}
-	csum = (__force u32)csum_partial(buf_align, size, 0);
+	csum = (__force u32)cksm(buf_align, size, 0);
 	if (csum != os_info_old->entry[nr].csum) {
 		msg = "checksum failed";
 		goto fail_free;