mmc: mmc_spi: Enable stable writes

While using the mmc_spi driver occasionally errors like this popped up:

mmcblk0: error -84 transferring data end_request: I/O error, dev mmcblk0, sector 581756

I looked on the Internet for occurrences of the same problem and came
across a helpful post [1]. It includes source code to reproduce the bug.
There is also an analysis about the cause. During transmission data in the
supplied buffer is being modified. Thus the previously calculated checksum
is not correct anymore.

After some digging I found out that device drivers are supposed to report
they need stable writes. To fix this I set the appropriate flag at queue
initialization if CRC checksumming is enabled for that SPI host.

[1]
https://groups.google.com/forum/#!msg/sim1/gLlzWeXGFr8/KevXinUXfc8J

Signed-off-by: Andreas Koop <[email protected]>
[shihpo: Rebase on top of v5.3-rc1]
Signed-off-by: ShihPo Hung <[email protected]>
Cc: Paul Walmsley <[email protected]>
CC: [email protected]
Signed-off-by: Ulf Hansson <[email protected]>

Author: Andreas Koop

drivers/mmc/core/queue.c

@@ -10,6 +10,7 @@
 #include <linux/kthread.h>
 #include <linux/scatterlist.h>
 #include <linux/dma-mapping.h>
+#include <linux/backing-dev.h>
 
 #include <linux/mmc/card.h>
 #include <linux/mmc/host.h>
@@ -427,6 +428,10 @@ int mmc_init_queue(struct mmc_queue *mq, struct mmc_card *card)
 		goto free_tag_set;
 	}
 
+	if (mmc_host_is_spi(host) && host->use_spi_crc)
+		mq->queue->backing_dev_info->capabilities |=
+			BDI_CAP_STABLE_WRITES;
+
 	mq->queue->queuedata = mq;
 	blk_queue_rq_timeout(mq->queue, 60 * HZ);