[U-Boot] [PATCH v2] Davinci: davinci_nand.c performance enhancments

[Nick Thompson <nick.thompson@ge.com>]

Introduces various optimisations that approximately triple the
read data rate from NAND when run on da830evm.

Most of these optimisations depend on the endianess of the machine
and most of them are very similar to optimisations already present
in the Linux Kernel.

Signed-off-by: Nick Thompson <nick.thompson@ge.com>
---
Changes:
	Cleaned up based on Scott Wood's comments:
	read/write_buf slightly faster and catches more cases.
	Removed unnecessary and/or badly named variables.

 drivers/mtd/nand/davinci_nand.c |  200 ++++++++++++++++++++++++++++-----------
 1 files changed, 146 insertions(+), 54 deletions(-)

diff --git a/drivers/mtd/nand/davinci_nand.c b/drivers/mtd/nand/davinci_nand.c
index 90e038e..bfc2acf 100644
--- a/drivers/mtd/nand/davinci_nand.c
+++ b/drivers/mtd/nand/davinci_nand.c
@@ -59,14 +59,111 @@
 
 static emif_registers *const emif_regs = (void *) DAVINCI_ASYNC_EMIF_CNTRL_BASE;
 
+/*
+ * Exploit the little endianness of the ARM to do multi-byte transfers
+ * per device read. This can perform over twice as quickly as individual
+ * byte transfers when buffer alignment is conducive.
+ *
+ * NOTE: This only works if the NAND is not connected to the 2 LSBs of
+ * the address bus. On Davinci EVM platforms this has always been true.
+ */
+static void nand_davinci_read_buf(struct mtd_info *mtd, uint8_t *buf, int len)
+{
+	struct nand_chip *chip = mtd->priv;
+	const u32 *nand = chip->IO_ADDR_R;
+
+	/* Make sure that buf is 32 bit aligned */
+	if (((int)buf & 0x3) != 0) {
+		if (((int)buf & 0x1) != 0) {
+			if (len) {
+				*buf = readb(nand);
+				buf += 1;
+				len--;
+			}
+		}
+
+		if (((int)buf & 0x3) != 0) {
+			if (len >= 2) {
+				*(u16 *)buf = readw(nand);
+				buf += 2;
+				len -= 2;
+			}
+		}
+	}
+
+	/* copy aligned data */
+	while (len >= 4) {
+		*(u32 *)buf = readl(nand);
+		buf += 4;
+		len -= 4;
+	}
+
+	/* mop up any remaining bytes */
+	if (len) {
+		if (len >= 2) {
+			*(u16 *)buf = readw(nand);
+			buf += 2;
+			len -= 2;
+		}
+
+		if (len)
+			*buf = readb(nand);
+	}
+}
+
+static void nand_davinci_write_buf(struct mtd_info *mtd, const uint8_t *buf,
+				   int len)
+{
+	struct nand_chip *chip = mtd->priv;
+	const u32 *nand = chip->IO_ADDR_W;
+
+	/* Make sure that buf is 32 bit aligned */
+	if (((int)buf & 0x3) != 0) {
+		if (((int)buf & 0x1) != 0) {
+			if (len) {
+				writeb(*buf, nand);
+				buf += 1;
+				len--;
+			}
+		}
+
+		if (((int)buf & 0x3) != 0) {
+			if (len >= 2) {
+				writew(*(u16 *)buf, nand);
+				buf += 2;
+				len -= 2;
+			}
+		}
+	}
+
+	/* copy aligned data */
+	while (len >= 4) {
+		writel(*(u32 *)buf, nand);
+		buf += 4;
+		len -= 4;
+	}
+
+	/* mop up any remaining bytes */
+	if (len) {
+		if (len >= 2) {
+			writew(*(u16 *)buf, nand);
+			buf += 2;
+			len -= 2;
+		}
+
+		if (len)
+			writeb(*buf, nand);
+	}
+}
+
 static void nand_davinci_hwcontrol(struct mtd_info *mtd, int cmd, unsigned int ctrl)
 {
 	struct		nand_chip *this = mtd->priv;
 	u_int32_t	IO_ADDR_W = (u_int32_t)this->IO_ADDR_W;
 
-	IO_ADDR_W &= ~(MASK_ALE|MASK_CLE);
-
 	if (ctrl & NAND_CTRL_CHANGE) {
+		IO_ADDR_W &= ~(MASK_ALE|MASK_CLE);
+
 		if ( ctrl & NAND_CLE )
 			IO_ADDR_W |= MASK_CLE;
 		if ( ctrl & NAND_ALE )
@@ -75,7 +172,7 @@ static void nand_davinci_hwcontrol(struct mtd_info *mtd, int cmd, unsigned int c
 	}
 
 	if (cmd != NAND_CMD_NONE)
-		writeb(cmd, this->IO_ADDR_W);
+		writeb(cmd, IO_ADDR_W);
 }
 
 #ifdef CONFIG_SYS_NAND_HW_ECC
@@ -247,59 +344,55 @@ static int nand_davinci_4bit_calculate_ecc(struct mtd_info *mtd,
 					   const uint8_t *dat,
 					   uint8_t *ecc_code)
 {
-	unsigned int hw_4ecc[4] = { 0, 0, 0, 0 };
-	unsigned int const1 = 0, const2 = 0;
-	unsigned char count1 = 0;
+	unsigned int hw_4ecc[4];
+	unsigned int i;
 
 	nand_davinci_4bit_readecc(mtd, hw_4ecc);
 
 	/*Convert 10 bit ecc value to 8 bit */
-	for (count1 = 0; count1 < 2; count1++) {
-		const2 = count1 * 5;
-		const1 = count1 * 2;
+	for (i = 0; i < 2; i++) {
+		unsigned int hw_ecc_low = hw_4ecc[i * 2];
+		unsigned int hw_ecc_hi = hw_4ecc[(i * 2) + 1];
 
 		/* Take first 8 bits from val1 (count1=0) or val5 (count1=1) */
-		ecc_code[const2] = hw_4ecc[const1] & 0xFF;
+		*ecc_code++ = hw_ecc_low & 0xFF;
 
 		/*
 		 * Take 2 bits as LSB bits from val1 (count1=0) or val5
 		 * (count1=1) and 6 bits from val2 (count1=0) or
 		 * val5 (count1=1)
 		 */
-		ecc_code[const2 + 1] =
-		    ((hw_4ecc[const1] >> 8) & 0x3) | ((hw_4ecc[const1] >> 14) &
-						      0xFC);
+		*ecc_code++ =
+		    ((hw_ecc_low >> 8) & 0x3) | ((hw_ecc_low >> 14) & 0xFC);
 
 		/*
 		 * Take 4 bits from val2 (count1=0) or val5 (count1=1) and
 		 * 4 bits from val3 (count1=0) or val6 (count1=1)
 		 */
-		ecc_code[const2 + 2] =
-		    ((hw_4ecc[const1] >> 22) & 0xF) |
-		    ((hw_4ecc[const1 + 1] << 4) & 0xF0);
+		*ecc_code++ =
+		    ((hw_ecc_low >> 22) & 0xF) | ((hw_ecc_hi << 4) & 0xF0);
 
 		/*
 		 * Take 6 bits from val3(count1=0) or val6 (count1=1) and
 		 * 2 bits from val4 (count1=0) or  val7 (count1=1)
 		 */
-		ecc_code[const2 + 3] =
-		    ((hw_4ecc[const1 + 1] >> 4) & 0x3F) |
-		    ((hw_4ecc[const1 + 1] >> 10) & 0xC0);
+		*ecc_code++ =
+		    ((hw_ecc_hi >> 4) & 0x3F) | ((hw_ecc_hi >> 10) & 0xC0);
 
 		/* Take 8 bits from val4 (count1=0) or val7 (count1=1) */
-		ecc_code[const2 + 4] = (hw_4ecc[const1 + 1] >> 18) & 0xFF;
+		*ecc_code++ = (hw_ecc_hi >> 18) & 0xFF;
 	}
+
 	return 0;
 }
 
-
 static int nand_davinci_4bit_correct_data(struct mtd_info *mtd, uint8_t *dat,
 					  uint8_t *read_ecc, uint8_t *calc_ecc)
 {
-	unsigned short ecc_10bit[8] = { 0, 0, 0, 0, 0, 0, 0, 0 };
 	int i;
-	unsigned int hw_4ecc[4] = { 0, 0, 0, 0 }, iserror = 0;
-	unsigned short *pspare = NULL, *pspare1 = NULL;
+	unsigned int hw_4ecc[4];
+	unsigned int iserror;
+	unsigned short *ecc16;
 	unsigned int numerrors, erroraddress, errorvalue;
 	u32 val;
 
@@ -316,44 +409,41 @@ static int nand_davinci_4bit_correct_data(struct mtd_info *mtd, uint8_t *dat,
 		return 0;
 
 	/* Convert 8 bit in to 10 bit */
-	pspare = (unsigned short *)&read_ecc[2];
-	pspare1 = (unsigned short *)&read_ecc[0];
+	ecc16 = (unsigned short *)&read_ecc[0];
 
-	/* Take 10 bits from 0th and 1st bytes */
-	ecc_10bit[0] = (*pspare1) & 0x3FF;
+	/*
+	 * Write the parity values in the NAND Flash 4-bit ECC Load register.
+	 * Write each parity value one at a time starting from 4bit_ecc_val8
+	 * to 4bit_ecc_val1.
+	 */
 
-	/* Take 6 bits from 1st byte and 4 bits from 2nd byte */
-	ecc_10bit[1] = (((*pspare1) >> 10) & 0x3F)
-	    | (((pspare[0]) << 6) & 0x3C0);
+	/*Take 2 bits from 8th byte and 8 bits from 9th byte */
+	writel(((ecc16[4]) >> 6) & 0x3FF, &emif_regs->NAND4BITECCLOAD);
 
-	/* Take 4 bits form 2nd bytes and 6 bits from 3rd bytes */
-	ecc_10bit[2] = ((pspare[0]) >> 4) & 0x3FF;
+	/* Take 4 bits from 7th byte and 6 bits from 8th byte */
+	writel((((ecc16[3]) >> 12) & 0xF) | ((((ecc16[4])) << 4) & 0x3F0),
+	       &emif_regs->NAND4BITECCLOAD);
 
-	/*Take 2 bits from 3rd byte and 8 bits from 4th byte */
-	ecc_10bit[3] = (((pspare[0]) >> 14) & 0x3)
-	    | ((((pspare[1])) << 2) & 0x3FC);
+	/* Take 6 bits from 6th byte and 4 bits from 7th byte */
+	writel((ecc16[3] >> 2) & 0x3FF, &emif_regs->NAND4BITECCLOAD);
 
 	/* Take 8 bits from 5th byte and 2 bits from 6th byte */
-	ecc_10bit[4] = ((pspare[1]) >> 8)
-	    | ((((pspare[2])) << 8) & 0x300);
+	writel(((ecc16[2]) >> 8) | ((((ecc16[3])) << 8) & 0x300),
+	       &emif_regs->NAND4BITECCLOAD);
 
-	/* Take 6 bits from 6th byte and 4 bits from 7th byte */
-	ecc_10bit[5] = (pspare[2] >> 2) & 0x3FF;
+	/*Take 2 bits from 3rd byte and 8 bits from 4th byte */
+	writel((((ecc16[1]) >> 14) & 0x3) | ((((ecc16[2])) << 2) & 0x3FC),
+	       &emif_regs->NAND4BITECCLOAD);
 
-	/* Take 4 bits from 7th byte and 6 bits from 8th byte */
-	ecc_10bit[6] = (((pspare[2]) >> 12) & 0xF)
-	    | ((((pspare[3])) << 4) & 0x3F0);
+	/* Take 4 bits form 2nd bytes and 6 bits from 3rd bytes */
+	writel(((ecc16[1]) >> 4) & 0x3FF, &emif_regs->NAND4BITECCLOAD);
 
-	/*Take 2 bits from 8th byte and 8 bits from 9th byte */
-	ecc_10bit[7] = ((pspare[3]) >> 6) & 0x3FF;
+	/* Take 6 bits from 1st byte and 4 bits from 2nd byte */
+	writel((((ecc16[0]) >> 10) & 0x3F) | (((ecc16[1]) << 6) & 0x3C0),
+	       &emif_regs->NAND4BITECCLOAD);
 
-	/*
-	 * Write the parity values in the NAND Flash 4-bit ECC Load register.
-	 * Write each parity value one at a time starting from 4bit_ecc_val8
-	 * to 4bit_ecc_val1.
-	 */
-	for (i = 7; i >= 0; i--)
-		emif_regs->NAND4BITECCLOAD = ecc_10bit[i];
+	/* Take 10 bits from 0th and 1st bytes */
+	writel((ecc16[0]) & 0x3FF, &emif_regs->NAND4BITECCLOAD);
 
 	/*
 	 * Perform a dummy read to the EMIF Revision Code and Status register.
@@ -370,8 +460,7 @@ static int nand_davinci_4bit_correct_data(struct mtd_info *mtd, uint8_t *dat,
 	 */
 	nand_davinci_4bit_readecc(mtd, hw_4ecc);
 
-	if (hw_4ecc[0] == ECC_STATE_NO_ERR && hw_4ecc[1] == ECC_STATE_NO_ERR &&
-	    hw_4ecc[2] == ECC_STATE_NO_ERR && hw_4ecc[3] == ECC_STATE_NO_ERR)
+	if (!(hw_4ecc[0] | hw_4ecc[1] | hw_4ecc[2] | hw_4ecc[3]))
 		return 0;
 
 	/*
@@ -518,6 +607,9 @@ void davinci_nand_init(struct nand_chip *nand)
 	/* Set address of hardware control function */
 	nand->cmd_ctrl = nand_davinci_hwcontrol;
 
+	nand->read_buf = nand_davinci_read_buf;
+	nand->write_buf = nand_davinci_write_buf;
+
 	nand->dev_ready = nand_davinci_dev_ready;
 
 	nand_flash_init();
-- 
1.6.3.3