[PATCH] NAND: Fix NAND ECC errors on AMD Au1550

[Sergei Shtylylov <sshtylyov@ru.mvista.com>]

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Hello.

          (This is a follow-up to the older thread:
http://lists.infradead.org/pipermail/linux-mtd/2005-October/013983.html)

          Reintroducing the problem: the static bus controller fails to keep
-CE asserted during chip ready delay on read commands (the NAND chip being
used requires this). So, the current driver allows nand_base.c to drive -CE
manually (during the whole sector read). When the PCMCIA driver is enabled
however, occasionally the ECC errors occur on NAND reads. This happens because
PCMCIA driver polls sockets periodically and reads one of the board's
control/status regs (BCSRs) which are accessible via the same static bus
as the NAND flash using the different chip select (and the NOR flash is
accessible the same way), so as the NAND driver forces NAND chip select
asserted and the -RE signal is shared, there's a contention 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 proved to work: to force -CE asserted only
while we're waiting for NAND chip to become ready after a read command,
disabling interrupts for a maximum of 25 microsecs (according to Toshiba
TC58DVM92A1FT00 flash chip datasheet). So, here's the initial patch which
I'm hoping to have made looking more decently...

WBR, Sergei



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Signed-off-by: Konstantin Baydarov <kbaidarov@ru.mvista.com>
Signed-off-by: Sergei Shtylyov <sshtylyov@ru.mvista.com>

Index: drivers/mtd/nand/au1550nd.c
===================================================================
RCS file: /home/cvs/mtd/drivers/mtd/nand/au1550nd.c,v
retrieving revision 1.12
diff -a -u -p -r1.12 au1550nd.c
--- drivers/mtd/nand/au1550nd.c	23 Sep 2005 01:44:55 -0000	1.12
+++ drivers/mtd/nand/au1550nd.c	29 Oct 2005 20:04:23 -0000
@@ -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>
@@ -313,6 +314,141 @@ int au1550_device_ready(struct mtd_info 
 	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 @@ 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;