NAND: Fix NAND ECC errors on AMD Au1550

    On AMD Au1550 the static bus controller fails to keep -CE asserted during
chip ready delay on read commands and the NAND chip being used requires this.
So, the current driver allows nand_base.c to drive -CE manually during the
entire sector read. When the PCMCIA driver is enabled however, occasionally
the ECC errors occur on NAND reads. This happens because the PCMCIA driver
polls sockets periodically and reads one of the board's control/status regs
(BCSRs) which are on the same static bus as the NAND flash, and just use
another chip select (and the NOR flash also resides on that bus), so as the
NAND driver forces NAND chip select asserted and the -RE signal is shared, a
contention occurs on the static bus when BCSR or NOR flash is read while we're
reading from NAND.
    So, we either can't keep interrupts enabled during the whole NAND sector
read (which is hardly acceptable), or have to implement some interlocking
scheme between multiple drivers (which is painful, and makes me shudder :-).
    There's a third way which has proven to work: to force -CE asserted only
while we're waiting for a NAND chip to become ready after a read command,
disabling interrupts for a maximum of 25 microseconds (according to Toshiba
TC58DVM92A1FT00 datasheet -- this chip is mentioned in the board schematics);
for Samsung NAND chip which seems to be actually used this delay is even less,
12 us.

Signed-off-by: Konstantin Baydarov <kbaidarov@ru.mvista.com>
Signed-off-by: Sergei Shtylyov <sshtylyov@ru.mvista.com>
Signed-off-by: David Woodhouse <dwmw2@infradead.org>

drivers/mtd/nand/au1550nd.c

@@ -14,6 +14,7 @@
 #include <linux/slab.h>
 #include <linux/init.h>
 #include <linux/module.h>
+#include <linux/interrupt.h>
 #include <linux/mtd/mtd.h>
 #include <linux/mtd/nand.h>
 #include <linux/mtd/partitions.h>
@@ -318,6 +319,141 @@ int au1550_device_ready(struct mtd_info *mtd)
 	return ret;
 }
 
+/**
+ * au1550_select_chip - control -CE line
+ *	Forbid driving -CE manually permitting the NAND controller to do this.
+ *	Keeping -CE asserted during the whole sector reads interferes with the
+ *	NOR flash and PCMCIA drivers as it causes contention on the static bus.
+ *	We only have to hold -CE low for the NAND read commands since the flash
+ *	chip needs it to be asserted during chip not ready time but the NAND
+ *	controller keeps it released.
+ *
+ * @mtd:	MTD device structure
+ * @chip:	chipnumber to select, -1 for deselect
+ */
+static void au1550_select_chip(struct mtd_info *mtd, int chip)
+{
+}
+
+/**
+ * au1550_command - Send command to NAND device
+ * @mtd:	MTD device structure
+ * @command:	the command to be sent
+ * @column:	the column address for this command, -1 if none
+ * @page_addr:	the page address for this command, -1 if none
+ */
+static void au1550_command(struct mtd_info *mtd, unsigned command, int column, int page_addr)
+{
+	register struct nand_chip *this = mtd->priv;
+	int ce_override = 0, i;
+	ulong flags;
+
+	/* Begin command latch cycle */
+	this->hwcontrol(mtd, NAND_CTL_SETCLE);
+	/*
+	 * Write out the command to the device.
+	 */
+	if (command == NAND_CMD_SEQIN) {
+		int readcmd;
+
+		if (column >= mtd->oobblock) {
+			/* OOB area */
+			column -= mtd->oobblock;
+			readcmd = NAND_CMD_READOOB;
+		} else if (column < 256) {
+			/* First 256 bytes --> READ0 */
+			readcmd = NAND_CMD_READ0;
+		} else {
+			column -= 256;
+			readcmd = NAND_CMD_READ1;
+		}
+		this->write_byte(mtd, readcmd);
+	}
+	this->write_byte(mtd, command);
+
+	/* Set ALE and clear CLE to start address cycle */
+	this->hwcontrol(mtd, NAND_CTL_CLRCLE);
+
+	if (column != -1 || page_addr != -1) {
+		this->hwcontrol(mtd, NAND_CTL_SETALE);
+
+		/* Serially input address */
+		if (column != -1) {
+			/* Adjust columns for 16 bit buswidth */
+			if (this->options & NAND_BUSWIDTH_16)
+				column >>= 1;
+			this->write_byte(mtd, column);
+		}
+		if (page_addr != -1) {
+			this->write_byte(mtd, (u8)(page_addr & 0xff));
+
+			if (command == NAND_CMD_READ0 ||
+			    command == NAND_CMD_READ1 ||
+			    command == NAND_CMD_READOOB) {
+				/*
+				 * NAND controller will release -CE after
+				 * the last address byte is written, so we'll
+				 * have to forcibly assert it. No interrupts
+				 * are allowed while we do this as we don't
+				 * want the NOR flash or PCMCIA drivers to
+				 * steal our precious bytes of data...
+				 */
+				ce_override = 1;
+				local_irq_save(flags);
+				this->hwcontrol(mtd, NAND_CTL_SETNCE);
+			}
+
+			this->write_byte(mtd, (u8)(page_addr >> 8));
+
+			/* One more address cycle for devices > 32MiB */
+			if (this->chipsize > (32 << 20))
+				this->write_byte(mtd, (u8)((page_addr >> 16) & 0x0f));
+		}
+		/* Latch in address */
+		this->hwcontrol(mtd, NAND_CTL_CLRALE);
+	}
+
+	/*
+	 * Program and erase have their own busy handlers.
+	 * Status and sequential in need no delay.
+	 */
+	switch (command) {
+
+	case NAND_CMD_PAGEPROG:
+	case NAND_CMD_ERASE1:
+	case NAND_CMD_ERASE2:
+	case NAND_CMD_SEQIN:
+	case NAND_CMD_STATUS:
+		return;
+
+	case NAND_CMD_RESET:
+		break;
+
+	case NAND_CMD_READ0:
+	case NAND_CMD_READ1:
+	case NAND_CMD_READOOB:
+		/* Check if we're really driving -CE low (just in case) */
+		if (unlikely(!ce_override))
+			break;
+
+		/* Apply a short delay always to ensure that we do wait tWB. */
+		ndelay(100);
+		/* Wait for a chip to become ready... */
+		for (i = this->chip_delay; !this->dev_ready(mtd) && i > 0; --i)
+			udelay(1);
+
+		/* Release -CE and re-enable interrupts. */
+		this->hwcontrol(mtd, NAND_CTL_CLRNCE);
+		local_irq_restore(flags);
+		return;
+	}
+	/* Apply this short delay always to ensure that we do wait tWB. */
+	ndelay(100);
+
+	while(!this->dev_ready(mtd));
+}
+
+
 /*
  * Main initialization routine
  */
@@ -437,6 +573,9 @@ static int __init au1xxx_nand_init(void)
 	/* Set address of hardware control function */
 	this->hwcontrol = au1550_hwcontrol;
 	this->dev_ready = au1550_device_ready;
+	this->select_chip = au1550_select_chip;
+	this->cmdfunc = au1550_command;
+
 	/* 30 us command delay time */
 	this->chip_delay = 30;
 	this->eccmode = NAND_ECC_SOFT;