mmc_write.c: Make mmc_berase do 32bit safe 64bit math

We want to see if the requested start or total block count are
unaligned.  We discard the whole numbers and only care about the
remainder.  Update the code to use div_u64_rem here and add a comment.

Cc: Hans de Goede <hdegoede@redhat.com>
Cc: Pantelis Antoniou <pantelis.antoniou@konsulko.com>
Cc: Bernhard Nortmann <bernhard.nortmann@web.de>
Reported-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Tom Rini <trini@konsulko.com>
Tested-by: Bernhard Nortmann <bernhard.nortmann@web.de>
Reviewed-by: Hans de Goede <hdegoede@redhat.com>

drivers/mmc/mmc_write.c

@@ -10,6 +10,8 @@
 #include <config.h>
 #include <common.h>
 #include <part.h>
+#include <div64.h>
+#include <linux/math64.h>
 #include "mmc_private.h"
 
 static ulong mmc_erase_t(struct mmc *mmc, ulong start, lbaint_t blkcnt)
@@ -66,6 +68,7 @@ err_out:
 unsigned long mmc_berase(int dev_num, lbaint_t start, lbaint_t blkcnt)
 {
 	int err = 0;
+	u32 start_rem, blkcnt_rem;
 	struct mmc *mmc = find_mmc_device(dev_num);
 	lbaint_t blk = 0, blk_r = 0;
 	int timeout = 1000;
@@ -73,7 +76,14 @@ unsigned long mmc_berase(int dev_num, lbaint_t start, lbaint_t blkcnt)
 	if (!mmc)
 		return -1;
 
-	if ((start % mmc->erase_grp_size) || (blkcnt % mmc->erase_grp_size))
+	/*
+	 * We want to see if the requested start or total block count are
+	 * unaligned.  We discard the whole numbers and only care about the
+	 * remainder.
+	 */
+	err = div_u64_rem(start, mmc->erase_grp_size, &start_rem);
+	err = div_u64_rem(blkcnt, mmc->erase_grp_size, &blkcnt_rem);
+	if (start_rem || blkcnt_rem)
 		printf("\n\nCaution! Your devices Erase group is 0x%x\n"
 		       "The erase range would be change to "
 		       "0x" LBAF "~0x" LBAF "\n\n",