mmc: dw_mmc: handle data blocks > than 4kB if IDMAC is used

As per DW MobileStorage databook "each descriptor can transfer up to 4kB
of data in chained mode", moreover buffer size that is put in "des1" is
limited to 13 bits, i.e. for example on attempt to
IDMAC_SET_BUFFER1_SIZE(desc, 8192) size value that's effectively written
will be 0.

On the platform with 8kB PAGE_SIZE I see dw_mmc gets data blocks in
SG-list of 8kB size and that leads to unpredictable behavior of the
SD/MMC controller.

In particular on write to FAT partition of SD-card the controller will
stuck in the middle of DMA transaction.

Solution to the problem is simple - we need to pass large (> 4kB) data
buffers to the controller via multiple descriptors. And that's what
that change does.

What's interesting I did try original driver on same platform but
configured with 4kB PAGE_SIZE and may confirm that data blocks passed
in SG-list to dw_mmc never exeed 4kB limit - that explains why nobody
ever faced a problem I did.

Signed-off-by: Alexey Brodkin <[email protected]>
Cc: [email protected]

Author: abrodkin

drivers/mmc/host/dw_mmc.c

@@ -80,6 +80,9 @@ struct idmac_desc {
 
 	u32		des3;	/* buffer 2 physical address */
 };
+
+/* Each descriptor can transfer up to 4KB of data in chained mode */
+#define DW_MCI_DESC_DATA_LENGTH	0x1000
 #endif /* CONFIG_MMC_DW_IDMAC */
 
 static bool dw_mci_reset(struct dw_mci *host);
@@ -414,30 +417,49 @@ static void dw_mci_translate_sglist(struct dw_mci *host, struct mmc_data *data,
 				    unsigned int sg_len)
 {
 	int i;
-	struct idmac_desc *desc = host->sg_cpu;
+	unsigned int desc_len;
+	struct idmac_desc *desc_first, *desc_last, *desc;
+
+	desc_first = desc_last = desc = host->sg_cpu;
 
-	for (i = 0; i < sg_len; i++, desc++) {
+	for (i = 0; i < sg_len; i++) {
 		unsigned int length = sg_dma_len(&data->sg[i]);
 		u32 mem_addr = sg_dma_address(&data->sg[i]);
 
-		/* Set the OWN bit and disable interrupts for this descriptor */
-		desc->des0 = IDMAC_DES0_OWN | IDMAC_DES0_DIC | IDMAC_DES0_CH;
+		for ( ; length ; desc++) {
+			/* Make sure we're not putting too much of data */
+			desc_len = (length <= DW_MCI_DESC_DATA_LENGTH) ?
+				   length : DW_MCI_DESC_DATA_LENGTH;
+
+			length -= desc_len;
 
-		/* Buffer length */
-		IDMAC_SET_BUFFER1_SIZE(desc, length);
+			/*
+			 * Set the OWN bit and disable interrupts
+			 * for this descriptor
+			 */
+			desc->des0 = IDMAC_DES0_OWN | IDMAC_DES0_DIC |
+				     IDMAC_DES0_CH;
 
-		/* Physical address to DMA to/from */
-		desc->des2 = mem_addr;
+			/* Buffer length */
+			IDMAC_SET_BUFFER1_SIZE(desc, desc_len);
+
+			/* Physical address to DMA to/from */
+			desc->des2 = mem_addr;
+
+			/* Update physical address for the next descriptor */
+			mem_addr += desc_len;
+
+			/* Save pointer to the last descriptor */
+			desc_last = desc;
+		}
 	}
 
 	/* Set first descriptor */
-	desc = host->sg_cpu;
-	desc->des0 |= IDMAC_DES0_FD;
+	desc_first->des0 |= IDMAC_DES0_FD;
 
 	/* Set last descriptor */
-	desc = host->sg_cpu + (i - 1) * sizeof(struct idmac_desc);
-	desc->des0 &= ~(IDMAC_DES0_CH | IDMAC_DES0_DIC);
-	desc->des0 |= IDMAC_DES0_LD;
+	desc_last->des0 &= ~(IDMAC_DES0_CH | IDMAC_DES0_DIC);
+	desc_last->des0 |= IDMAC_DES0_LD;
 
 	wmb();
 }
@@ -2274,7 +2296,7 @@ static int dw_mci_init_slot(struct dw_mci *host, unsigned int id)
 		mmc->max_segs = host->ring_size;
 		mmc->max_blk_size = 65536;
 		mmc->max_blk_count = host->ring_size;
-		mmc->max_seg_size = 0x1000;
+		mmc->max_seg_size = DW_MCI_DESC_DATA_LENGTH;
 		mmc->max_req_size = mmc->max_seg_size * mmc->max_blk_count;
 #else
 		mmc->max_segs = 64;