mmc: mmc_test: make performance test area size about 4MiB

The test area size was set to the preferred erase size but for comparison
purposes it is better if it is the same size for different devices.  Make
it a multiple of preferred erase size that is greater than or equal to 4MiB.
Signed-off-by: Adrian Hunter <adrian.hunter@nokia.com>
Signed-off-by: Chris Ball <cjb@laptop.org>

drivers/mmc/card/mmc_test.c

@@ -1426,28 +1426,29 @@ static int mmc_test_area_cleanup(struct mmc_test_card *test)
 }
 
 /*
- * Initialize an area for testing large transfers.  The size of the area is the
- * preferred erase size which is a good size for optimal transfer speed.  Note
- * that is typically 4MiB for modern cards.  The test area is set to the middle
- * of the card because cards may have different charateristics at the front
- * (for FAT file system optimization).  Optionally, the area is erased (if the
- * card supports it) which may improve write performance.  Optionally, the area
- * is filled with data for subsequent read tests.
+ * Initialize an area for testing large transfers.  The test area is set to the
+ * middle of the card because cards may have different charateristics at the
+ * front (for FAT file system optimization).  Optionally, the area is erased
+ * (if the card supports it) which may improve write performance.  Optionally,
+ * the area is filled with data for subsequent read tests.
  */
 static int mmc_test_area_init(struct mmc_test_card *test, int erase, int fill)
 {
 	struct mmc_test_area *t = &test->area;
-	unsigned long min_sz = 64 * 1024;
+	unsigned long min_sz = 64 * 1024, sz;
 	int ret;
 
 	ret = mmc_test_set_blksize(test, 512);
 	if (ret)
 		return ret;
 
-	if (test->card->pref_erase > TEST_AREA_MAX_SIZE >> 9)
-		t->max_sz = TEST_AREA_MAX_SIZE;
-	else
-		t->max_sz = (unsigned long)test->card->pref_erase << 9;
+	/* Make the test area size about 4MiB */
+	sz = (unsigned long)test->card->pref_erase << 9;
+	t->max_sz = sz;
+	while (t->max_sz < 4 * 1024 * 1024)
+		t->max_sz += sz;
+	while (t->max_sz > TEST_AREA_MAX_SIZE && t->max_sz > sz)
+		t->max_sz -= sz;
 
 	t->max_segs = test->card->host->max_segs;
 	t->max_seg_sz = test->card->host->max_seg_size;