mmc: mxcmmc: Use sg_miter for PIO

Use the scatterlist memory iterator instead of just
dereferencing virtual memory using sg_virt().
This make highmem references work properly.

Since this driver is using a worker, no atomic trickery
is needed.
Suggested-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/linux-mmc/20240122073423.GA25859@lst.de/Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Link: https://lore.kernel.org/r/20240127-mmc-proper-kmap-v2-6-d8e732aa97d1@linaro.orgSigned-off-by: Ulf Hansson <ulf.hansson@linaro.org>

drivers/mmc/host/mxcmmc.c

@@ -266,11 +266,18 @@ static inline void buffer_swap32(u32 *buf, int len)
 
 static void mxcmci_swap_buffers(struct mmc_data *data)
 {
-	struct scatterlist *sg;
-	int i;
+	struct sg_mapping_iter sgm;
+	u32 *buf;
+
+	sg_miter_start(&sgm, data->sg, data->sg_len,
+		       SG_MITER_TO_SG | SG_MITER_FROM_SG);
+
+	while (sg_miter_next(&sgm)) {
+		buf = sgm.addr;
+		buffer_swap32(buf, sgm.length);
+	}
 
-	for_each_sg(data->sg, sg, data->sg_len, i)
-		buffer_swap32(sg_virt(sg), sg->length);
+	sg_miter_stop(&sgm);
 }
 #else
 static inline void mxcmci_swap_buffers(struct mmc_data *data) {}
@@ -526,10 +533,9 @@ static int mxcmci_poll_status(struct mxcmci_host *host, u32 mask)
 	} while (1);
 }
 
-static int mxcmci_pull(struct mxcmci_host *host, void *_buf, int bytes)
+static int mxcmci_pull(struct mxcmci_host *host, u32 *buf, int bytes)
 {
 	unsigned int stat;
-	u32 *buf = _buf;
 
 	while (bytes > 3) {
 		stat = mxcmci_poll_status(host,
@@ -555,10 +561,9 @@ static int mxcmci_pull(struct mxcmci_host *host, void *_buf, int bytes)
 	return 0;
 }
 
-static int mxcmci_push(struct mxcmci_host *host, void *_buf, int bytes)
+static int mxcmci_push(struct mxcmci_host *host, u32 *buf, int bytes)
 {
 	unsigned int stat;
-	u32 *buf = _buf;
 
 	while (bytes > 3) {
 		stat = mxcmci_poll_status(host, STATUS_BUF_WRITE_RDY);
@@ -586,31 +591,39 @@ static int mxcmci_push(struct mxcmci_host *host, void *_buf, int bytes)
 static int mxcmci_transfer_data(struct mxcmci_host *host)
 {
 	struct mmc_data *data = host->req->data;
-	struct scatterlist *sg;
-	int stat, i;
+	struct sg_mapping_iter sgm;
+	int stat;
+	u32 *buf;
 
 	host->data = data;
 	host->datasize = 0;
+	sg_miter_start(&sgm, data->sg, data->sg_len,
+		       (data->flags & MMC_DATA_READ) ? SG_MITER_TO_SG : SG_MITER_FROM_SG);
 
 	if (data->flags & MMC_DATA_READ) {
-		for_each_sg(data->sg, sg, data->sg_len, i) {
-			stat = mxcmci_pull(host, sg_virt(sg), sg->length);
+		while (sg_miter_next(&sgm)) {
+			buf = sgm.addr;
+			stat = mxcmci_pull(host, buf, sgm.length);
 			if (stat)
-				return stat;
-			host->datasize += sg->length;
+				goto transfer_error;
+			host->datasize += sgm.length;
 		}
 	} else {
-		for_each_sg(data->sg, sg, data->sg_len, i) {
-			stat = mxcmci_push(host, sg_virt(sg), sg->length);
+		while (sg_miter_next(&sgm)) {
+			buf = sgm.addr;
+			stat = mxcmci_push(host, buf, sgm.length);
 			if (stat)
-				return stat;
-			host->datasize += sg->length;
+				goto transfer_error;
+			host->datasize += sgm.length;
 		}
 		stat = mxcmci_poll_status(host, STATUS_WRITE_OP_DONE);
 		if (stat)
-			return stat;
+			goto transfer_error;
 	}
-	return 0;
+
+transfer_error:
+	sg_miter_stop(&sgm);
+	return stat;
 }
 
 static void mxcmci_datawork(struct work_struct *work)