mtd: rawnand: arasan: Support the hardware BCH ECC engine

Add support for the hardware ECC BCH engine.

Please mind that this engine has an important limitation:
BCH implementation does not inform the user when an uncorrectable ECC
error occurs. To workaround this, we avoid using the hardware engine
in the read path and do the computation with the software BCH
implementation, which is faster than mixing hardware (for correction)
and software (for verification).
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Reviewed-by: Boris Brezillon <boris.brezillon@collabora.com>
Link: https://lore.kernel.org/linux-mtd/20200519074549.23673-9-miquel.raynal@bootlin.com

drivers/mtd/nand/raw/Kconfig

@@ -456,6 +456,7 @@ config MTD_NAND_CADENCE
 config MTD_NAND_ARASAN
 	tristate "Support for Arasan NAND flash controller"
 	depends on HAS_IOMEM && HAS_DMA
+	select BCH
 	help
 	  Enables the driver for the Arasan NAND flash controller on
 	  Zynq Ultrascale+ MPSoC.

drivers/mtd/nand/raw/arasan-nand-controller.c

@@ -10,6 +10,7 @@
  *   Naga Sureshkumar Relli <nagasure@xilinx.com>
  */
 
+#include <linux/bch.h>
 #include <linux/bitfield.h>
 #include <linux/clk.h>
 #include <linux/delay.h>
@@ -144,6 +145,11 @@ struct anfc_op {
  * @strength:		Register value of the ECC strength
  * @raddr_cycles:	Row address cycle information
  * @caddr_cycles:	Column address cycle information
+ * @ecc_bits:		Exact number of ECC bits per syndrome
+ * @ecc_total:		Total number of ECC bytes
+ * @errloc:		Array of errors located with soft BCH
+ * @hw_ecc:		Buffer to store syndromes computed by hardware
+ * @bch:		BCH structure
  */
 struct anand {
 	struct list_head node;
@@ -157,6 +163,11 @@ struct anand {
 	u32 strength;
 	u16 raddr_cycles;
 	u16 caddr_cycles;
+	unsigned int ecc_bits;
+	unsigned int ecc_total;
+	unsigned int *errloc;
+	u8 *hw_ecc;
+	struct bch_control *bch;
 };
 
 /**
@@ -261,6 +272,194 @@ static int anfc_pkt_len_config(unsigned int len, unsigned int *steps,
 	return 0;
 }
 
+/*
+ * When using the embedded hardware ECC engine, the controller is in charge of
+ * feeding the engine with, first, the ECC residue present in the data array.
+ * A typical read operation is:
+ * 1/ Assert the read operation by sending the relevant command/address cycles
+ *    but targeting the column of the first ECC bytes in the OOB area instead of
+ *    the main data directly.
+ * 2/ After having read the relevant number of ECC bytes, the controller uses
+ *    the RNDOUT/RNDSTART commands which are set into the "ECC Spare Command
+ *    Register" to move the pointer back at the beginning of the main data.
+ * 3/ It will read the content of the main area for a given size (pktsize) and
+ *    will feed the ECC engine with this buffer again.
+ * 4/ The ECC engine derives the ECC bytes for the given data and compare them
+ *    with the ones already received. It eventually trigger status flags and
+ *    then set the "Buffer Read Ready" flag.
+ * 5/ The corrected data is then available for reading from the data port
+ *    register.
+ *
+ * The hardware BCH ECC engine is known to be inconstent in BCH mode and never
+ * reports uncorrectable errors. Because of this bug, we have to use the
+ * software BCH implementation in the read path.
+ */
+static int anfc_read_page_hw_ecc(struct nand_chip *chip, u8 *buf,
+				 int oob_required, int page)
+{
+	struct arasan_nfc *nfc = to_anfc(chip->controller);
+	struct mtd_info *mtd = nand_to_mtd(chip);
+	struct anand *anand = to_anand(chip);
+	unsigned int len = mtd->writesize + (oob_required ? mtd->oobsize : 0);
+	unsigned int max_bitflips = 0;
+	dma_addr_t dma_addr;
+	int step, ret;
+	struct anfc_op nfc_op = {
+		.pkt_reg =
+			PKT_SIZE(chip->ecc.size) |
+			PKT_STEPS(chip->ecc.steps),
+		.addr1_reg =
+			(page & 0xFF) << (8 * (anand->caddr_cycles)) |
+			(((page >> 8) & 0xFF) << (8 * (1 + anand->caddr_cycles))),
+		.addr2_reg =
+			((page >> 16) & 0xFF) |
+			ADDR2_STRENGTH(anand->strength) |
+			ADDR2_CS(anand->cs),
+		.cmd_reg =
+			CMD_1(NAND_CMD_READ0) |
+			CMD_2(NAND_CMD_READSTART) |
+			CMD_PAGE_SIZE(anand->page_sz) |
+			CMD_DMA_ENABLE |
+			CMD_NADDRS(anand->caddr_cycles +
+				   anand->raddr_cycles),
+		.prog_reg = PROG_PGRD,
+	};
+
+	dma_addr = dma_map_single(nfc->dev, (void *)buf, len, DMA_FROM_DEVICE);
+	if (dma_mapping_error(nfc->dev, dma_addr)) {
+		dev_err(nfc->dev, "Buffer mapping error");
+		return -EIO;
+	}
+
+	writel_relaxed(lower_32_bits(dma_addr), nfc->base + DMA_ADDR0_REG);
+	writel_relaxed(upper_32_bits(dma_addr), nfc->base + DMA_ADDR1_REG);
+
+	anfc_trigger_op(nfc, &nfc_op);
+
+	ret = anfc_wait_for_event(nfc, XFER_COMPLETE);
+	dma_unmap_single(nfc->dev, dma_addr, len, DMA_FROM_DEVICE);
+	if (ret) {
+		dev_err(nfc->dev, "Error reading page %d\n", page);
+		return ret;
+	}
+
+	/* Store the raw OOB bytes as well */
+	ret = nand_change_read_column_op(chip, mtd->writesize, chip->oob_poi,
+					 mtd->oobsize, 0);
+	if (ret)
+		return ret;
+
+	/*
+	 * For each step, compute by softare the BCH syndrome over the raw data.
+	 * Compare the theoretical amount of errors and compare with the
+	 * hardware engine feedback.
+	 */
+	for (step = 0; step < chip->ecc.steps; step++) {
+		u8 *raw_buf = &buf[step * chip->ecc.size];
+		unsigned int bit, byte;
+		int bf, i;
+
+		/* Extract the syndrome, it is not necessarily aligned */
+		memset(anand->hw_ecc, 0, chip->ecc.bytes);
+		nand_extract_bits(anand->hw_ecc, 0,
+				  &chip->oob_poi[mtd->oobsize - anand->ecc_total],
+				  anand->ecc_bits * step, anand->ecc_bits);
+
+		bf = bch_decode(anand->bch, raw_buf, chip->ecc.size,
+				anand->hw_ecc, NULL, NULL, anand->errloc);
+		if (!bf) {
+			continue;
+		} else if (bf > 0) {
+			for (i = 0; i < bf; i++) {
+				/* Only correct the data, not the syndrome */
+				if (anand->errloc[i] < (chip->ecc.size * 8)) {
+					bit = BIT(anand->errloc[i] & 7);
+					byte = anand->errloc[i] >> 3;
+					raw_buf[byte] ^= bit;
+				}
+			}
+
+			mtd->ecc_stats.corrected += bf;
+			max_bitflips = max_t(unsigned int, max_bitflips, bf);
+
+			continue;
+		}
+
+		bf = nand_check_erased_ecc_chunk(raw_buf, chip->ecc.size,
+						 NULL, 0, NULL, 0,
+						 chip->ecc.strength);
+		if (bf > 0) {
+			mtd->ecc_stats.corrected += bf;
+			max_bitflips = max_t(unsigned int, max_bitflips, bf);
+			memset(raw_buf, 0xFF, chip->ecc.size);
+		} else if (bf < 0) {
+			mtd->ecc_stats.failed++;
+		}
+	}
+
+	return 0;
+}
+
+static int anfc_write_page_hw_ecc(struct nand_chip *chip, const u8 *buf,
+				  int oob_required, int page)
+{
+	struct anand *anand = to_anand(chip);
+	struct arasan_nfc *nfc = to_anfc(chip->controller);
+	struct mtd_info *mtd = nand_to_mtd(chip);
+	unsigned int len = mtd->writesize + (oob_required ? mtd->oobsize : 0);
+	dma_addr_t dma_addr;
+	int ret;
+	struct anfc_op nfc_op = {
+		.pkt_reg =
+			PKT_SIZE(chip->ecc.size) |
+			PKT_STEPS(chip->ecc.steps),
+		.addr1_reg =
+			(page & 0xFF) << (8 * (anand->caddr_cycles)) |
+			(((page >> 8) & 0xFF) << (8 * (1 + anand->caddr_cycles))),
+		.addr2_reg =
+			((page >> 16) & 0xFF) |
+			ADDR2_STRENGTH(anand->strength) |
+			ADDR2_CS(anand->cs),
+		.cmd_reg =
+			CMD_1(NAND_CMD_SEQIN) |
+			CMD_2(NAND_CMD_PAGEPROG) |
+			CMD_PAGE_SIZE(anand->page_sz) |
+			CMD_DMA_ENABLE |
+			CMD_NADDRS(anand->caddr_cycles +
+				   anand->raddr_cycles) |
+			CMD_ECC_ENABLE,
+		.prog_reg = PROG_PGPROG,
+	};
+
+	writel_relaxed(anand->ecc_conf, nfc->base + ECC_CONF_REG);
+	writel_relaxed(ECC_SP_CMD1(NAND_CMD_RNDIN) |
+		       ECC_SP_ADDRS(anand->caddr_cycles),
+		       nfc->base + ECC_SP_REG);
+
+	dma_addr = dma_map_single(nfc->dev, (void *)buf, len, DMA_TO_DEVICE);
+	if (dma_mapping_error(nfc->dev, dma_addr)) {
+		dev_err(nfc->dev, "Buffer mapping error");
+		return -EIO;
+	}
+
+	writel_relaxed(lower_32_bits(dma_addr), nfc->base + DMA_ADDR0_REG);
+	writel_relaxed(upper_32_bits(dma_addr), nfc->base + DMA_ADDR1_REG);
+
+	anfc_trigger_op(nfc, &nfc_op);
+	ret = anfc_wait_for_event(nfc, XFER_COMPLETE);
+	dma_unmap_single(nfc->dev, dma_addr, len, DMA_TO_DEVICE);
+	if (ret) {
+		dev_err(nfc->dev, "Error writing page %d\n", page);
+		return ret;
+	}
+
+	/* Spare data is not protected */
+	if (oob_required)
+		ret = nand_write_oob_std(chip, page);
+
+	return ret;
+}
+
 /* NAND framework ->exec_op() hooks and related helpers */
 static int anfc_parse_instructions(struct nand_chip *chip,
 				   const struct nand_subop *subop,
@@ -681,6 +880,138 @@ static int anfc_setup_data_interface(struct nand_chip *chip, int target,
 	return 0;
 }
 
+static int anfc_calc_hw_ecc_bytes(int step_size, int strength)
+{
+	unsigned int bch_gf_mag, ecc_bits;
+
+	switch (step_size) {
+	case SZ_512:
+		bch_gf_mag = 13;
+		break;
+	case SZ_1K:
+		bch_gf_mag = 14;
+		break;
+	default:
+		return -EINVAL;
+	}
+
+	ecc_bits = bch_gf_mag * strength;
+
+	return DIV_ROUND_UP(ecc_bits, 8);
+}
+
+static const int anfc_hw_ecc_512_strengths[] = {4, 8, 12};
+
+static const int anfc_hw_ecc_1024_strengths[] = {24};
+
+static const struct nand_ecc_step_info anfc_hw_ecc_step_infos[] = {
+	{
+		.stepsize = SZ_512,
+		.strengths = anfc_hw_ecc_512_strengths,
+		.nstrengths = ARRAY_SIZE(anfc_hw_ecc_512_strengths),
+	},
+	{
+		.stepsize = SZ_1K,
+		.strengths = anfc_hw_ecc_1024_strengths,
+		.nstrengths = ARRAY_SIZE(anfc_hw_ecc_1024_strengths),
+	},
+};
+
+static const struct nand_ecc_caps anfc_hw_ecc_caps = {
+	.stepinfos = anfc_hw_ecc_step_infos,
+	.nstepinfos = ARRAY_SIZE(anfc_hw_ecc_step_infos),
+	.calc_ecc_bytes = anfc_calc_hw_ecc_bytes,
+};
+
+static int anfc_init_hw_ecc_controller(struct arasan_nfc *nfc,
+				       struct nand_chip *chip)
+{
+	struct anand *anand = to_anand(chip);
+	struct mtd_info *mtd = nand_to_mtd(chip);
+	struct nand_ecc_ctrl *ecc = &chip->ecc;
+	unsigned int bch_prim_poly = 0, bch_gf_mag = 0, ecc_offset;
+	int ret;
+
+	switch (mtd->writesize) {
+	case SZ_512:
+	case SZ_2K:
+	case SZ_4K:
+	case SZ_8K:
+	case SZ_16K:
+		break;
+	default:
+		dev_err(nfc->dev, "Unsupported page size %d\n", mtd->writesize);
+		return -EINVAL;
+	}
+
+	ret = nand_ecc_choose_conf(chip, &anfc_hw_ecc_caps, mtd->oobsize);
+	if (ret)
+		return ret;
+
+	switch (ecc->strength) {
+	case 12:
+		anand->strength = 0x1;
+		break;
+	case 8:
+		anand->strength = 0x2;
+		break;
+	case 4:
+		anand->strength = 0x3;
+		break;
+	case 24:
+		anand->strength = 0x4;
+		break;
+	default:
+		dev_err(nfc->dev, "Unsupported strength %d\n", ecc->strength);
+		return -EINVAL;
+	}
+
+	switch (ecc->size) {
+	case SZ_512:
+		bch_gf_mag = 13;
+		bch_prim_poly = 0x201b;
+		break;
+	case SZ_1K:
+		bch_gf_mag = 14;
+		bch_prim_poly = 0x4443;
+		break;
+	default:
+		dev_err(nfc->dev, "Unsupported step size %d\n", ecc->strength);
+		return -EINVAL;
+	}
+
+	mtd_set_ooblayout(mtd, &nand_ooblayout_lp_ops);
+
+	ecc->steps = mtd->writesize / ecc->size;
+	ecc->algo = NAND_ECC_BCH;
+	anand->ecc_bits = bch_gf_mag * ecc->strength;
+	ecc->bytes = DIV_ROUND_UP(anand->ecc_bits, 8);
+	anand->ecc_total = DIV_ROUND_UP(anand->ecc_bits * ecc->steps, 8);
+	ecc_offset = mtd->writesize + mtd->oobsize - anand->ecc_total;
+	anand->ecc_conf = ECC_CONF_COL(ecc_offset) |
+			  ECC_CONF_LEN(anand->ecc_total) |
+			  ECC_CONF_BCH_EN;
+
+	anand->errloc = devm_kmalloc_array(nfc->dev, ecc->strength,
+					   sizeof(*anand->errloc), GFP_KERNEL);
+	if (!anand->errloc)
+		return -ENOMEM;
+
+	anand->hw_ecc = devm_kmalloc(nfc->dev, ecc->bytes, GFP_KERNEL);
+	if (!anand->hw_ecc)
+		return -ENOMEM;
+
+	/* Enforce bit swapping to fit the hardware */
+	anand->bch = bch_init(bch_gf_mag, ecc->strength, bch_prim_poly, true);
+	if (!anand->bch)
+		return -EINVAL;
+
+	ecc->read_page = anfc_read_page_hw_ecc;
+	ecc->write_page = anfc_write_page_hw_ecc;
+
+	return 0;
+}
+
 static int anfc_attach_chip(struct nand_chip *chip)
 {
 	struct anand *anand = to_anand(chip);
@@ -731,6 +1062,8 @@ static int anfc_attach_chip(struct nand_chip *chip)
 	case NAND_ECC_ON_DIE:
 		break;
 	case NAND_ECC_HW:
+		ret = anfc_init_hw_ecc_controller(nfc, chip);
+		break;
 	default:
 		dev_err(nfc->dev, "Unsupported ECC mode: %d\n",
 			chip->ecc.mode);
@@ -740,10 +1073,19 @@ static int anfc_attach_chip(struct nand_chip *chip)
 	return ret;
 }
 
+static void anfc_detach_chip(struct nand_chip *chip)
+{
+	struct anand *anand = to_anand(chip);
+
+	if (anand->bch)
+		bch_free(anand->bch);
+}
+
 static const struct nand_controller_ops anfc_ops = {
 	.exec_op = anfc_exec_op,
 	.setup_data_interface = anfc_setup_data_interface,
 	.attach_chip = anfc_attach_chip,
+	.detach_chip = anfc_detach_chip,
 };
 
 static int anfc_chip_init(struct arasan_nfc *nfc, struct device_node *np)