mtd: nand: pxa3xx_nand: add support for partial chunks

This commit is needed to properly support the 8-bits ECC configuration
with 4KB pages.

When pages larger than 2 KB are used on platforms using the PXA3xx
NAND controller, the reading/programming operations need to be split
in chunks of 2 KBs or less because the controller FIFO is limited to
about 2 KB (i.e a bit more than 2 KB to accommodate OOB data). Due to
this requirement, the data layout on NAND is a bit strange, with ECC
interleaved with data, at the end of each chunk.

When a 4-bits ECC configuration is used with 4 KB pages, the physical
data layout on the NAND looks like this:

| 2048 data | 32 spare | 30 ECC | 2048 data | 32 spare | 30 ECC |

So the data chunks have an equal size, 2080 bytes for each chunk,
which the driver supports properly.

When a 8-bits ECC configuration is used with 4KB pages, the physical
data layout on the NAND looks like this:

| 1024 data | 30 ECC | 1024 data | 30 ECC | 1024 data | 30 ECC | 1024 data | 30 ECC | 64 spare | 30 ECC |

So, the spare area is stored in its own chunk, which has a different
size than the other chunks. Since OOB is not used by UBIFS, the initial
implementation of the driver has chosen to not support reading this
additional "spare" chunk of data.

Unfortunately, Marvell has chosen to store the BBT signature in the
OOB area. Therefore, if the driver doesn't read this spare area, Linux
has no way of finding the BBT. It thinks there is no BBT, and rewrites
one, which U-Boot does not recognize, causing compatibility problems
between the bootloader and the kernel in terms of NAND usage.

To fix this, this commit implements the support for reading a partial
last chunk. This support is currently only useful for the case of 8
bits ECC with 4 KB pages, but it will be useful in the future to
enable other configurations such as 12 bits and 16 bits ECC with 4 KB
pages, or 8 bits ECC with 8 KB pages, etc. All those configurations
have a "last" chunk that doesn't have the same size as the other
chunks.

In order to implement reading of the last chunk, this commit:

 - Adds a number of new fields to the pxa3xx_nand_info to describe how
   many full chunks and how many chunks we have, the size of full
   chunks and partial chunks, both in terms of data area and spare
   area.

 - Fills in the step_chunk_size and step_spare_size variables to
   describe how much data and spare should be read/written for the
   current read/program step.

 - Reworks the state machine to accommodate doing the additional read
   or program step when a last partial chunk is used.

This commit has been tested on a Marvell Armada 398 DB board, with a
4KB page NAND, tested in both 4 bits ECC and 8 bits ECC
configurations. Robert Jarzmik has tested on some PXA platforms.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Tested-by: Robert Jarzmik <robert.jarzmik@free.fr>
Acked-by: Ezequiel Garcia <ezequiel@vanguardiasur.com.ar>
Signed-off-by: Brian Norris <computersforpeace@gmail.com>

drivers/mtd/nand/pxa3xx_nand.c

@@ -234,15 +234,44 @@ struct pxa3xx_nand_info {
 	int			use_spare;	/* use spare ? */
 	int			need_wait;
 
-	unsigned int		data_size;	/* data to be read from FIFO */
-	unsigned int		chunk_size;	/* split commands chunk size */
-	unsigned int		oob_size;
+	/* Amount of real data per full chunk */
+	unsigned int		chunk_size;
+
+	/* Amount of spare data per full chunk */
 	unsigned int		spare_size;
+
+	/* Number of full chunks (i.e chunk_size + spare_size) */
+	unsigned int            nfullchunks;
+
+	/*
+	 * Total number of chunks. If equal to nfullchunks, then there
+	 * are only full chunks. Otherwise, there is one last chunk of
+	 * size (last_chunk_size + last_spare_size)
+	 */
+	unsigned int            ntotalchunks;
+
+	/* Amount of real data in the last chunk */
+	unsigned int		last_chunk_size;
+
+	/* Amount of spare data in the last chunk */
+	unsigned int		last_spare_size;
+
 	unsigned int		ecc_size;
 	unsigned int		ecc_err_cnt;
 	unsigned int		max_bitflips;
 	int 			retcode;
 
+	/*
+	 * Variables only valid during command
+	 * execution. step_chunk_size and step_spare_size is the
+	 * amount of real data and spare data in the current
+	 * chunk. cur_chunk is the current chunk being
+	 * read/programmed.
+	 */
+	unsigned int		step_chunk_size;
+	unsigned int		step_spare_size;
+	unsigned int            cur_chunk;
+
 	/* cached register value */
 	uint32_t		reg_ndcr;
 	uint32_t		ndtr0cs0;
@@ -538,25 +567,6 @@ static int pxa3xx_nand_init(struct pxa3xx_nand_host *host)
 	return 0;
 }
 
-/*
- * Set the data and OOB size, depending on the selected
- * spare and ECC configuration.
- * Only applicable to READ0, READOOB and PAGEPROG commands.
- */
-static void pxa3xx_set_datasize(struct pxa3xx_nand_info *info,
-				struct mtd_info *mtd)
-{
-	int oob_enable = info->reg_ndcr & NDCR_SPARE_EN;
-
-	info->data_size = mtd->writesize;
-	if (!oob_enable)
-		return;
-
-	info->oob_size = info->spare_size;
-	if (!info->use_ecc)
-		info->oob_size += info->ecc_size;
-}
-
 /**
  * NOTE: it is a must to set ND_RUN firstly, then write
  * command buffer, otherwise, it does not work.
@@ -672,28 +682,28 @@ static void drain_fifo(struct pxa3xx_nand_info *info, void *data, int len)
 
 static void handle_data_pio(struct pxa3xx_nand_info *info)
 {
-	unsigned int do_bytes = min(info->data_size, info->chunk_size);
-
 	switch (info->state) {
 	case STATE_PIO_WRITING:
-		writesl(info->mmio_base + NDDB,
-			info->data_buff + info->data_buff_pos,
-			DIV_ROUND_UP(do_bytes, 4));
+		if (info->step_chunk_size)
+			writesl(info->mmio_base + NDDB,
+				info->data_buff + info->data_buff_pos,
+				DIV_ROUND_UP(info->step_chunk_size, 4));
 
-		if (info->oob_size > 0)
+		if (info->step_spare_size)
 			writesl(info->mmio_base + NDDB,
 				info->oob_buff + info->oob_buff_pos,
-				DIV_ROUND_UP(info->oob_size, 4));
+				DIV_ROUND_UP(info->step_spare_size, 4));
 		break;
 	case STATE_PIO_READING:
-		drain_fifo(info,
-			   info->data_buff + info->data_buff_pos,
-			   DIV_ROUND_UP(do_bytes, 4));
+		if (info->step_chunk_size)
+			drain_fifo(info,
+				   info->data_buff + info->data_buff_pos,
+				   DIV_ROUND_UP(info->step_chunk_size, 4));
 
-		if (info->oob_size > 0)
+		if (info->step_spare_size)
 			drain_fifo(info,
 				   info->oob_buff + info->oob_buff_pos,
-				   DIV_ROUND_UP(info->oob_size, 4));
+				   DIV_ROUND_UP(info->step_spare_size, 4));
 		break;
 	default:
 		dev_err(&info->pdev->dev, "%s: invalid state %d\n", __func__,
@@ -702,9 +712,8 @@ static void handle_data_pio(struct pxa3xx_nand_info *info)
 	}
 
 	/* Update buffer pointers for multi-page read/write */
-	info->data_buff_pos += do_bytes;
-	info->oob_buff_pos += info->oob_size;
-	info->data_size -= do_bytes;
+	info->data_buff_pos += info->step_chunk_size;
+	info->oob_buff_pos += info->step_spare_size;
 }
 
 static void pxa3xx_nand_data_dma_irq(void *data)
@@ -745,8 +754,9 @@ static void start_data_dma(struct pxa3xx_nand_info *info)
 				info->state);
 		BUG();
 	}
-	info->sg.length = info->data_size +
-		(info->oob_size ? info->spare_size + info->ecc_size : 0);
+	info->sg.length = info->chunk_size;
+	if (info->use_spare)
+		info->sg.length += info->spare_size + info->ecc_size;
 	dma_map_sg(info->dma_chan->device->dev, &info->sg, 1, info->dma_dir);
 
 	tx = dmaengine_prep_slave_sg(info->dma_chan, &info->sg, 1, direction,
@@ -907,9 +917,11 @@ static void prepare_start_command(struct pxa3xx_nand_info *info, int command)
 	/* reset data and oob column point to handle data */
 	info->buf_start		= 0;
 	info->buf_count		= 0;
-	info->oob_size		= 0;
 	info->data_buff_pos	= 0;
 	info->oob_buff_pos	= 0;
+	info->step_chunk_size   = 0;
+	info->step_spare_size   = 0;
+	info->cur_chunk         = 0;
 	info->use_ecc		= 0;
 	info->use_spare		= 1;
 	info->retcode		= ERR_NONE;
@@ -921,8 +933,6 @@ static void prepare_start_command(struct pxa3xx_nand_info *info, int command)
 	case NAND_CMD_READ0:
 	case NAND_CMD_PAGEPROG:
 		info->use_ecc = 1;
-	case NAND_CMD_READOOB:
-		pxa3xx_set_datasize(info, mtd);
 		break;
 	case NAND_CMD_PARAM:
 		info->use_spare = 0;
@@ -981,6 +991,14 @@ static int prepare_set_command(struct pxa3xx_nand_info *info, int command,
 		if (command == NAND_CMD_READOOB)
 			info->buf_start += mtd->writesize;
 
+		if (info->cur_chunk < info->nfullchunks) {
+			info->step_chunk_size = info->chunk_size;
+			info->step_spare_size = info->spare_size;
+		} else {
+			info->step_chunk_size = info->last_chunk_size;
+			info->step_spare_size = info->last_spare_size;
+		}
+
 		/*
 		 * Multiple page read needs an 'extended command type' field,
 		 * which is either naked-read or last-read according to the
@@ -992,8 +1010,8 @@ static int prepare_set_command(struct pxa3xx_nand_info *info, int command,
 			info->ndcb0 |= NDCB0_DBC | (NAND_CMD_READSTART << 8)
 					| NDCB0_LEN_OVRD
 					| NDCB0_EXT_CMD_TYPE(ext_cmd_type);
-			info->ndcb3 = info->chunk_size +
-				      info->oob_size;
+			info->ndcb3 = info->step_chunk_size +
+				info->step_spare_size;
 		}
 
 		set_command_address(info, mtd->writesize, column, page_addr);
@@ -1013,8 +1031,6 @@ static int prepare_set_command(struct pxa3xx_nand_info *info, int command,
 				| NDCB0_EXT_CMD_TYPE(ext_cmd_type)
 				| addr_cycle
 				| command;
-			/* No data transfer in this case */
-			info->data_size = 0;
 			exec_cmd = 1;
 		}
 		break;
@@ -1026,6 +1042,14 @@ static int prepare_set_command(struct pxa3xx_nand_info *info, int command,
 			break;
 		}
 
+		if (info->cur_chunk < info->nfullchunks) {
+			info->step_chunk_size = info->chunk_size;
+			info->step_spare_size = info->spare_size;
+		} else {
+			info->step_chunk_size = info->last_chunk_size;
+			info->step_spare_size = info->last_spare_size;
+		}
+
 		/* Second command setting for large pages */
 		if (mtd->writesize > PAGE_CHUNK_SIZE) {
 			/*
@@ -1036,14 +1060,14 @@ static int prepare_set_command(struct pxa3xx_nand_info *info, int command,
 			info->ndcb0 |= NDCB0_CMD_TYPE(0x1)
 					| NDCB0_LEN_OVRD
 					| NDCB0_EXT_CMD_TYPE(ext_cmd_type);
-			info->ndcb3 = info->chunk_size +
-				      info->oob_size;
+			info->ndcb3 = info->step_chunk_size +
+				      info->step_spare_size;
 
 			/*
 			 * This is the command dispatch that completes a chunked
 			 * page program operation.
 			 */
-			if (info->data_size == 0) {
+			if (info->cur_chunk == info->ntotalchunks) {
 				info->ndcb0 = NDCB0_CMD_TYPE(0x1)
 					| NDCB0_EXT_CMD_TYPE(ext_cmd_type)
 					| command;
@@ -1070,7 +1094,7 @@ static int prepare_set_command(struct pxa3xx_nand_info *info, int command,
 				| command;
 		info->ndcb1 = (column & 0xFF);
 		info->ndcb3 = INIT_BUFFER_SIZE;
-		info->data_size = INIT_BUFFER_SIZE;
+		info->step_chunk_size = INIT_BUFFER_SIZE;
 		break;
 
 	case NAND_CMD_READID:
@@ -1080,7 +1104,7 @@ static int prepare_set_command(struct pxa3xx_nand_info *info, int command,
 				| command;
 		info->ndcb1 = (column & 0xFF);
 
-		info->data_size = 8;
+		info->step_chunk_size = 8;
 		break;
 	case NAND_CMD_STATUS:
 		info->buf_count = 1;
@@ -1088,7 +1112,7 @@ static int prepare_set_command(struct pxa3xx_nand_info *info, int command,
 				| NDCB0_ADDR_CYC(1)
 				| command;
 
-		info->data_size = 8;
+		info->step_chunk_size = 8;
 		break;
 
 	case NAND_CMD_ERASE1:
@@ -1229,6 +1253,7 @@ static void nand_cmdfunc_extended(struct mtd_info *mtd,
 	init_completion(&info->dev_ready);
 	do {
 		info->state = STATE_PREPARED;
+
 		exec_cmd = prepare_set_command(info, command, ext_cmd_type,
 					       column, page_addr);
 		if (!exec_cmd) {
@@ -1248,22 +1273,30 @@ static void nand_cmdfunc_extended(struct mtd_info *mtd,
 			break;
 		}
 
+		/* Only a few commands need several steps */
+		if (command != NAND_CMD_PAGEPROG &&
+		    command != NAND_CMD_READ0    &&
+		    command != NAND_CMD_READOOB)
+			break;
+
+		info->cur_chunk++;
+
 		/* Check if the sequence is complete */
-		if (info->data_size == 0 && command != NAND_CMD_PAGEPROG)
+		if (info->cur_chunk == info->ntotalchunks && command != NAND_CMD_PAGEPROG)
 			break;
 
 		/*
 		 * After a splitted program command sequence has issued
 		 * the command dispatch, the command sequence is complete.
 		 */
-		if (info->data_size == 0 &&
+		if (info->cur_chunk == (info->ntotalchunks + 1) &&
 		    command == NAND_CMD_PAGEPROG &&
 		    ext_cmd_type == EXT_CMD_TYPE_DISPATCH)
 			break;
 
 		if (command == NAND_CMD_READ0 || command == NAND_CMD_READOOB) {
 			/* Last read: issue a 'last naked read' */
-			if (info->data_size == info->chunk_size)
+			if (info->cur_chunk == info->ntotalchunks - 1)
 				ext_cmd_type = EXT_CMD_TYPE_LAST_RW;
 			else
 				ext_cmd_type = EXT_CMD_TYPE_NAKED_RW;
@@ -1273,7 +1306,7 @@ static void nand_cmdfunc_extended(struct mtd_info *mtd,
 		 * the command dispatch must be issued to complete.
 		 */
 		} else if (command == NAND_CMD_PAGEPROG &&
-			   info->data_size == 0) {
+			   info->cur_chunk == info->ntotalchunks) {
 				ext_cmd_type = EXT_CMD_TYPE_DISPATCH;
 		}
 	} while (1);
@@ -1518,6 +1551,8 @@ static int pxa_ecc_init(struct pxa3xx_nand_info *info,
 			int strength, int ecc_stepsize, int page_size)
 {
 	if (strength == 1 && ecc_stepsize == 512 && page_size == 2048) {
+		info->nfullchunks = 1;
+		info->ntotalchunks = 1;
 		info->chunk_size = 2048;
 		info->spare_size = 40;
 		info->ecc_size = 24;
@@ -1526,6 +1561,8 @@ static int pxa_ecc_init(struct pxa3xx_nand_info *info,
 		ecc->strength = 1;
 
 	} else if (strength == 1 && ecc_stepsize == 512 && page_size == 512) {
+		info->nfullchunks = 1;
+		info->ntotalchunks = 1;
 		info->chunk_size = 512;
 		info->spare_size = 8;
 		info->ecc_size = 8;
@@ -1539,6 +1576,8 @@ static int pxa_ecc_init(struct pxa3xx_nand_info *info,
 	 */
 	} else if (strength == 4 && ecc_stepsize == 512 && page_size == 2048) {
 		info->ecc_bch = 1;
+		info->nfullchunks = 1;
+		info->ntotalchunks = 1;
 		info->chunk_size = 2048;
 		info->spare_size = 32;
 		info->ecc_size = 32;
@@ -1549,6 +1588,8 @@ static int pxa_ecc_init(struct pxa3xx_nand_info *info,
 
 	} else if (strength == 4 && ecc_stepsize == 512 && page_size == 4096) {
 		info->ecc_bch = 1;
+		info->nfullchunks = 2;
+		info->ntotalchunks = 2;
 		info->chunk_size = 2048;
 		info->spare_size = 32;
 		info->ecc_size = 32;
@@ -1563,8 +1604,12 @@ static int pxa_ecc_init(struct pxa3xx_nand_info *info,
 	 */
 	} else if (strength == 8 && ecc_stepsize == 512 && page_size == 4096) {
 		info->ecc_bch = 1;
+		info->nfullchunks = 4;
+		info->ntotalchunks = 5;
 		info->chunk_size = 1024;
 		info->spare_size = 0;
+		info->last_chunk_size = 0;
+		info->last_spare_size = 64;
 		info->ecc_size = 32;
 		ecc->mode = NAND_ECC_HW;
 		ecc->size = info->chunk_size;