Change the S3C SPI driver to use poll mode instead of interrupt mode.
This reduces the gap between bytes from about 2.25us [1] to 100ns [2].

[1] http://people.openmoko.org/werner/wlan-spi/spi-int.png
[2] http://people.openmoko.org/werner/wlan-spi/spi-poll.png

Index: korig/drivers/spi/spi_s3c24xx.c
===================================================================
--- korig.orig/drivers/spi/spi_s3c24xx.c	2008-09-27 22:45:38.000000000 -0300
+++ korig/drivers/spi/spi_s3c24xx.c	2008-09-27 22:46:45.000000000 -0300
@@ -56,7 +56,7 @@
 	struct s3c2410_spi_info *pdata;
 };
 
-#define SPCON_DEFAULT (S3C2410_SPCON_MSTR | S3C2410_SPCON_SMOD_INT)
+#define SPCON_DEFAULT (S3C2410_SPCON_MSTR | S3C2410_SPCON_SMOD_POLL)
 #define SPPIN_DEFAULT (S3C2410_SPPIN_KEEP)
 
 static inline struct s3c24xx_spi *to_hw(struct spi_device *sdev)
@@ -183,6 +183,7 @@
 static int s3c24xx_spi_txrx(struct spi_device *spi, struct spi_transfer *t)
 {
 	struct s3c24xx_spi *hw = to_hw(spi);
+	int i;
 
 	dev_dbg(&spi->dev, "txrx: tx %p, rx %p, len %d\n",
 		t->tx_buf, t->rx_buf, t->len);
@@ -194,9 +195,19 @@
 	hw->len = t->len;
 	hw->count = 0;
 
-	/* send the first byte */
-	writeb(hw_txbyte(hw, 0), hw->regs + S3C2410_SPTDAT);
-	wait_for_completion(&hw->done);
+	for (i = 0; i != t->len; i++) {
+		u8 spsta;
+
+		writeb(hw_txbyte(hw, i), hw->regs + S3C2410_SPTDAT);
+		do spsta = readb(hw->regs + S3C2410_SPSTA);
+		while (!(spsta & S3C2410_SPSTA_READY));
+		if (hw->rx) {
+			u8 b = readb(hw->regs + S3C2410_SPRDAT);
+
+			if (i)
+				hw->rx[i-1] = b;
+		}
+	}
 
 	/*
 	 * Get the last byte. Since we don't have more data we can send in
@@ -206,9 +217,9 @@
 	 * going on in the hardware. This is the voodoo ritual that makes it
 	 * work while anything else fails.
 	 */
-	if (hw->rx && hw->count) {
+	if (hw->rx && i) {
 		udelay(1+10*1000000/spi->max_speed_hz);
-		hw->rx[hw->count-1] = readb(hw->regs + S3C2410_SPRDAT);
+		hw->rx[i-1] = readb(hw->regs + S3C2410_SPRDAT);
 	}
 
 	if (0&&t->rx_buf && t->len > 18) {
@@ -219,7 +230,7 @@
 			printk(" %02x", ((u8 *) t->rx_buf)[i]);
 		printk("\n");
 	}
-	return hw->count;
+	return t->len;
 }
 
 static irqreturn_t s3c24xx_spi_irq(int irq, void *dev)
@@ -351,6 +362,7 @@
 		goto err_no_iomap;
 	}
 
+#if 0
 	hw->irq = platform_get_irq(pdev, 0);
 	if (hw->irq < 0) {
 		dev_err(&pdev->dev, "No IRQ specified\n");
@@ -363,6 +375,7 @@
 		dev_err(&pdev->dev, "Cannot claim IRQ\n");
 		goto err_no_irq;
 	}
+#endif
 
 	hw->clk = clk_get(&pdev->dev, "spi");
 	if (IS_ERR(hw->clk)) {
@@ -416,7 +429,7 @@
 	clk_put(hw->clk);
 
  err_no_clk:
-	free_irq(hw->irq, hw);
+	//free_irq(hw->irq, hw);
 
  err_no_irq:
 	iounmap(hw->regs);
@@ -444,7 +457,7 @@
 	clk_disable(hw->clk);
 	clk_put(hw->clk);
 
-	free_irq(hw->irq, hw);
+	//free_irq(hw->irq, hw);
 	iounmap(hw->regs);
 
 	release_resource(hw->ioarea);