mmc: omap: 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.
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-v2-7-d8e732aa97d1@linaro.orgSigned-off-by: Ulf Hansson <ulf.hansson@linaro.org>

drivers/mmc/host/omap.c

@@ -148,10 +148,8 @@ struct mmc_omap_host {
 	struct work_struct      send_stop_work;
 	struct mmc_data		*stop_data;
 
+	struct sg_mapping_iter	sg_miter;
 	unsigned int		sg_len;
-	int			sg_idx;
-	u16 *			buffer;
-	u32			buffer_bytes_left;
 	u32			total_bytes_left;
 
 	unsigned		features;
@@ -456,6 +454,8 @@ mmc_omap_xfer_done(struct mmc_omap_host *host, struct mmc_data *data)
 {
 	if (host->dma_in_use)
 		mmc_omap_release_dma(host, data, data->error);
+	else
+		sg_miter_stop(&host->sg_miter);
 
 	host->data = NULL;
 	host->sg_len = 0;
@@ -651,19 +651,6 @@ mmc_omap_cmd_timer(struct timer_list *t)
 	spin_unlock_irqrestore(&host->slot_lock, flags);
 }
 
-/* PIO only */
-static void
-mmc_omap_sg_to_buf(struct mmc_omap_host *host)
-{
-	struct scatterlist *sg;
-
-	sg = host->data->sg + host->sg_idx;
-	host->buffer_bytes_left = sg->length;
-	host->buffer = sg_virt(sg);
-	if (host->buffer_bytes_left > host->total_bytes_left)
-		host->buffer_bytes_left = host->total_bytes_left;
-}
-
 static void
 mmc_omap_clk_timer(struct timer_list *t)
 {
@@ -676,33 +663,37 @@ mmc_omap_clk_timer(struct timer_list *t)
 static void
 mmc_omap_xfer_data(struct mmc_omap_host *host, int write)
 {
+	struct sg_mapping_iter *sgm = &host->sg_miter;
 	int n, nwords;
+	u16 *buffer;
 
-	if (host->buffer_bytes_left == 0) {
-		host->sg_idx++;
-		BUG_ON(host->sg_idx == host->sg_len);
-		mmc_omap_sg_to_buf(host);
+	if (!sg_miter_next(sgm)) {
+		/* This should not happen */
+		dev_err(mmc_dev(host->mmc), "ran out of scatterlist prematurely\n");
+		return;
 	}
+	buffer = sgm->addr;
+
 	n = 64;
-	if (n > host->buffer_bytes_left)
-		n = host->buffer_bytes_left;
+	if (n > sgm->length)
+		n = sgm->length;
+	if (n > host->total_bytes_left)
+		n = host->total_bytes_left;
 
 	/* Round up to handle odd number of bytes to transfer */
 	nwords = DIV_ROUND_UP(n, 2);
 
-	host->buffer_bytes_left -= n;
+	sgm->consumed = n;
 	host->total_bytes_left -= n;
 	host->data->bytes_xfered += n;
 
 	if (write) {
 		__raw_writesw(host->virt_base + OMAP_MMC_REG(host, DATA),
-			      host->buffer, nwords);
+			      buffer, nwords);
 	} else {
 		__raw_readsw(host->virt_base + OMAP_MMC_REG(host, DATA),
-			     host->buffer, nwords);
+			     buffer, nwords);
 	}
-
-	host->buffer += nwords;
 }
 
 #ifdef CONFIG_MMC_DEBUG
@@ -956,6 +947,7 @@ static inline void set_data_timeout(struct mmc_omap_host *host, struct mmc_reque
 static void
 mmc_omap_prepare_data(struct mmc_omap_host *host, struct mmc_request *req)
 {
+	unsigned int miter_flags = SG_MITER_ATOMIC; /* Used from IRQ */
 	struct mmc_data *data = req->data;
 	int i, use_dma = 1, block_size;
 	struct scatterlist *sg;
@@ -990,7 +982,6 @@ mmc_omap_prepare_data(struct mmc_omap_host *host, struct mmc_request *req)
 		}
 	}
 
-	host->sg_idx = 0;
 	if (use_dma) {
 		enum dma_data_direction dma_data_dir;
 		struct dma_async_tx_descriptor *tx;
@@ -1071,7 +1062,11 @@ mmc_omap_prepare_data(struct mmc_omap_host *host, struct mmc_request *req)
 	OMAP_MMC_WRITE(host, BUF, 0x1f1f);
 	host->total_bytes_left = data->blocks * block_size;
 	host->sg_len = sg_len;
-	mmc_omap_sg_to_buf(host);
+	if (data->flags & MMC_DATA_READ)
+		miter_flags |= SG_MITER_TO_SG;
+	else
+		miter_flags |= SG_MITER_FROM_SG;
+	sg_miter_start(&host->sg_miter, data->sg, data->sg_len, miter_flags);
 	host->dma_in_use = 0;
 }