[PATCH v3 14/15] mtd: rawnand: sunxi: reduce user-data length register accesses

[James Hilliard]

DMA reads and writes clear every user-data length register and then
read-modify-write one field at a time. Multiple ECC steps share each
register, so this repeats MMIO accesses to the same words.

Build each register value in memory and write it once, including zero
lengths for unused slots. Reprogram every word for every DMA operation
instead of caching hardware state, so controller resets and switches
between chips need no special cache invalidation.

Share the length encoding with a PIO-specific setter. PIO always uses
hardware slot zero, and its page callbacks clear all length registers
before the chunk loop. Write the slot-zero value directly instead of
reading and modifying the same register for every chunk. Keep the
per-operation clearing so other slots remain zero after DMA fallback.

Signed-off-by: James Hilliard <james.hilliard1 at gmail.com>
---
 drivers/mtd/nand/raw/sunxi_nand.c | 73 +++++++++++++++++++++++++--------------
 1 file changed, 47 insertions(+), 26 deletions(-)

diff --git a/drivers/mtd/nand/raw/sunxi_nand.c b/drivers/mtd/nand/raw/sunxi_nand.c
index 9dc742ee4344..1c1fcea69108 100644
--- a/drivers/mtd/nand/raw/sunxi_nand.c
+++ b/drivers/mtd/nand/raw/sunxi_nand.c
@@ -996,35 +996,59 @@ static void sunxi_nfc_reset_user_data_len(struct sunxi_nfc *nfc)
 		writel(0, nfc->regs + NFC_REG_USER_DATA_LEN(nfc, i));
 }
 
-static void sunxi_nfc_set_user_data_len(struct sunxi_nfc *nfc,
-					int len, int hw_step)
+static int sunxi_nfc_user_data_len_code(struct sunxi_nfc *nfc, int len)
 {
-	bool found = false;
-	u32 val;
 	int i;
 
+	for (i = 0; i < nfc->caps->nuser_data_tab; i++) {
+		if (len == nfc->caps->user_data_len_tab[i])
+			return i;
+	}
+
+	dev_warn(nfc->dev, "Unsupported length for user data reg: %d\n", len);
+	return -EINVAL;
+}
+
+static void sunxi_nfc_set_user_data_len_pio(struct sunxi_nfc *nfc, int len)
+{
+	int code;
+
 	/* not all SoCs have this register */
 	if (!nfc->caps->reg_user_data_len)
 		return;
 
-	for (i = 0; i < nfc->caps->nuser_data_tab; i++) {
-		if (len == nfc->caps->user_data_len_tab[i]) {
-			found = true;
-			break;
-		}
-	}
-
-	if (!found) {
-		dev_warn(nfc->dev,
-			 "Unsupported length for user data reg: %d\n", len);
+	code = sunxi_nfc_user_data_len_code(nfc, len);
+	if (code < 0)
 		return;
-	}
 
-	val = readl(nfc->regs + NFC_REG_USER_DATA_LEN(nfc, hw_step));
+	/* PIO uses slot zero; the page callback clears all other slots. */
+	writel(FIELD_PREP(NFC_USER_DATA_LEN_MSK(0), code),
+	       nfc->regs + NFC_REG_USER_DATA_LEN(nfc, 0));
+}
+
+static void sunxi_nfc_set_user_data_len_dma(struct nand_chip *nand, int nchunks)
+{
+	struct sunxi_nand_chip *sunxi_nand = to_sunxi_nand(nand);
+	struct sunxi_nfc *nfc = to_sunxi_nfc(nand->controller);
+	int first, step, len, code;
+	u32 val;
+
+	if (!nfc->caps->reg_user_data_len)
+		return;
 
-	val &= ~NFC_USER_DATA_LEN_MSK(hw_step);
-	val |= field_prep(NFC_USER_DATA_LEN_MSK(hw_step), i);
-	writel(val, nfc->regs + NFC_REG_USER_DATA_LEN(nfc, hw_step));
+	/* Write each packed register once, including zeroes for unused slots. */
+	for (first = 0; first < nfc->caps->max_ecc_steps;
+	     first += NFC_REG_USER_DATA_LEN_CAPACITY) {
+		val = 0;
+		for (step = first; step < nchunks &&
+		     step < first + NFC_REG_USER_DATA_LEN_CAPACITY; step++) {
+			len = sunxi_nfc_user_data_sz(sunxi_nand, step);
+			code = sunxi_nfc_user_data_len_code(nfc, len);
+			if (code >= 0)
+				val |= field_prep(NFC_USER_DATA_LEN_MSK(step), code);
+		}
+		writel(val, nfc->regs + NFC_REG_USER_DATA_LEN(nfc, first));
+	}
 }
 
 static void sunxi_nfc_hw_ecc_set_prot_oob_bytes(struct nand_chip *nand,
@@ -1213,7 +1237,7 @@ static int sunxi_nfc_hw_ecc_read_chunk(struct nand_chip *nand,
 	if (ret)
 		return ret;
 
-	sunxi_nfc_set_user_data_len(nfc, user_data_sz, hw_step);
+	sunxi_nfc_set_user_data_len_pio(nfc, user_data_sz);
 	sunxi_nfc_randomizer_config(nand, page, false);
 	sunxi_nfc_randomizer_enable(nand);
 	writel(NFC_DATA_TRANS | NFC_DATA_SWAP_METHOD | NFC_ECC_OP,
@@ -1524,9 +1548,7 @@ static int sunxi_nfc_hw_ecc_read_chunks_dma(struct nand_chip *nand, uint8_t *buf
 		return ret;
 
 	sunxi_nfc_hw_ecc_enable(nand);
-	sunxi_nfc_reset_user_data_len(nfc);
-	for (i = 0; i < nchunks; i++)
-		sunxi_nfc_set_user_data_len(nfc, sunxi_nfc_user_data_sz(sunxi_nand, i), i);
+	sunxi_nfc_set_user_data_len_dma(nand, nchunks);
 	sunxi_nfc_randomizer_config(nand, page, false);
 	sunxi_nfc_randomizer_enable(nand);
 
@@ -1682,7 +1704,7 @@ static int sunxi_nfc_hw_ecc_write_chunk(struct nand_chip *nand,
 
 	sunxi_nfc_randomizer_config(nand, page, false);
 	sunxi_nfc_randomizer_enable(nand);
-	sunxi_nfc_set_user_data_len(nfc, user_data_sz, hw_step);
+	sunxi_nfc_set_user_data_len_pio(nfc, user_data_sz);
 	sunxi_nfc_hw_ecc_set_prot_oob_bytes(nand, oob, hw_step, bbm, page,
 					    user_data_sz);
 
@@ -1977,7 +1999,7 @@ static int sunxi_nfc_hw_ecc_write_page_dma(struct nand_chip *nand,
 	if (ret)
 		goto pio_fallback;
 
-	sunxi_nfc_reset_user_data_len(nfc);
+	sunxi_nfc_set_user_data_len_dma(nand, ecc->steps);
 	for (i = 0; i < ecc->steps; i++) {
 		unsigned int user_data_sz = sunxi_nfc_user_data_sz(sunxi_nand, i);
 		int oob_off = sunxi_get_oob_offset(sunxi_nand, ecc, i);
@@ -1985,7 +2007,6 @@ static int sunxi_nfc_hw_ecc_write_page_dma(struct nand_chip *nand,
 
 		sunxi_nfc_hw_ecc_set_prot_oob_bytes(nand, oob, i, !i, page,
 						    user_data_sz);
-		sunxi_nfc_set_user_data_len(nfc, user_data_sz, i);
 	}
 
 	ret = nand_prog_page_begin_op(nand, page, 0, NULL, 0);

-- 
2.53.0