mmc: queue: bring discard_granularity/alignment into line with SCSI

SCSI defines discard alignment as the offset to the first
optimal discard.  In the case of SD/MMC, that is always zero
which is the default.

SCSI defines discard granularity as a hint of a optimal
discard size.  That is much better expressed by the MMC
"preferred erase size" (pref_erase) field.

Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Signed-off-by: Chris Ball <cjb@laptop.org>

drivers/mmc/card/queue.c

@@ -135,12 +135,7 @@ int mmc_init_queue(struct mmc_queue *mq, struct mmc_card *card,
 		mq->queue->limits.max_discard_sectors = UINT_MAX;
 		if (card->erased_byte == 0)
 			mq->queue->limits.discard_zeroes_data = 1;
-		if (!mmc_can_trim(card) && is_power_of_2(card->erase_size)) {
-			mq->queue->limits.discard_granularity =
-							card->erase_size << 9;
-			mq->queue->limits.discard_alignment =
-							card->erase_size << 9;
-		}
+		mq->queue->limits.discard_granularity = card->pref_erase << 9;
 		if (mmc_can_secure_erase_trim(card))
 			queue_flag_set_unlocked(QUEUE_FLAG_SECDISCARD,
 						mq->queue);