Message-ID: <20090602203629.GM27332@atomide.com>
Date:	Tue, 2 Jun 2009 13:36:30 -0700
From:	Tony Lindgren <tony@...mide.com>
To:	vimal singh <vimalsingh@...com>
Cc:	linux-mtd@...ts.infradead.org, dwmw2@...radead.org,
	dedekind@...radead.org, david-b@...bell.net,
	linux-kernel@...r.kernel.org, linux-omap@...r.kernel.org
Subject: Re: [PATCH] [MTD] [NAND] Add prefetch and dma support for omap2/3
	NAND driver

* vimal singh <vimalsingh@...com> [090602 05:40]:
> This patch adds prefetch support to access nand flash in both mpu and dma mode.
> This patch also adds 8-bit nand support (omap_read/write_buf8).
> Prefetch can be used for both 8- and 16-bit devices.

This should be reviewed on the linux-omap@...r.kernel.org list for sure.
One other comment below.
 
> Signed-off-by: Vimal Singh <vimalsingh@...com>
> ---
> I prepared this patch on top of "OMAP2 / OMAP3 NAND driver" patch:
> http://lists.infradead.org/pipermail/linux-mtd/2009-May/025562.html
> 
> ---
>  arch/arm/mach-omap2/gpmc.c             |  102 ++++++++++
>  arch/arm/plat-omap/include/mach/gpmc.h |    4
>  drivers/mtd/nand/Kconfig               |   17 +
>  drivers/mtd/nand/omap2.c               |  308 ++++++++++++++++++++++++++++++++-
>  4 files changed, 422 insertions(+), 9 deletions(-)
> 
> Index: mtd-2.6/arch/arm/mach-omap2/gpmc.c
> ===================================================================
> --- mtd-2.6.orig/arch/arm/mach-omap2/gpmc.c
> +++ mtd-2.6/arch/arm/mach-omap2/gpmc.c
> @@ -54,6 +54,12 @@
>  #define GPMC_CHUNK_SHIFT	24		/* 16 MB */
>  #define GPMC_SECTION_SHIFT	28		/* 128 MB */
> 
> +#ifdef CONFIG_MTD_NAND_OMAP_PREFETCH
> +#define CS_NUM_SHIFT		24
> +#define ENABLE_PREFETCH		7
> +#define DMA_MPU_MODE		2
> +#endif
> +
>  static struct resource	gpmc_mem_root;
>  static struct resource	gpmc_cs_mem[GPMC_CS_NUM];
>  static DEFINE_SPINLOCK(gpmc_mem_lock);
> @@ -383,6 +389,99 @@ void gpmc_cs_free(int cs)
>  }
>  EXPORT_SYMBOL(gpmc_cs_free);
> 
> +#ifdef CONFIG_MTD_NAND_OMAP_PREFETCH
> +/**
> + * gpmc_prefetch_init - configures default configuration for prefetch engine
> + */
> +static void gpmc_prefetch_init(void)
> +{
> +	/* Setting the default threshold to 64 */
> +	gpmc_write_reg(GPMC_PREFETCH_CONTROL, 0x0);
> +	gpmc_write_reg(GPMC_PREFETCH_CONFIG1, 0x40  << 8);
> +	gpmc_write_reg(GPMC_PREFETCH_CONFIG2, 0x0);
> +}

Why would you want to have NAND specific init code int gpmc.c?

The purpose if gpmc.c is to provide access to configuring the
General Purpose Memory Controller (GPMC). You should just provide
functions in gpmc.c for the platform init code to use, and then
the drivers can stay platform independent.

Regards,

Tony


> +/**
> + * gpmc_prefetch_start - configures and starts prefetch transfer
> + * @cs: nand cs (chip select) number
> + * @dma_mode: dma mode enable (1) or disable (0)
> + * @u32_count: number of bytes to be transferred
> + * @is_write: prefetch read(0) or write post(1) mode
> + */
> +void gpmc_prefetch_start(int cs, int dma_mode,
> +				unsigned int u32_count, int is_write)
> +{
> +	uint32_t prefetch_config1;
> +	if (is_write) {
> +		/* Set the amount of bytes to be prefetched */
> +		gpmc_write_reg(GPMC_PREFETCH_CONFIG2, u32_count);
> +
> +		/* Set dma/mpu mode, the post write and enable the engine
> +		 * Set which cs is using the post write
> +		 */
> +		prefetch_config1 = gpmc_read_reg(GPMC_PREFETCH_CONFIG1);
> +		prefetch_config1 |= ((cs << CS_NUM_SHIFT) |
> +					(dma_mode << DMA_MPU_MODE) |
> +					(1 << ENABLE_PREFETCH) | 0x1);
> +		gpmc_write_reg(GPMC_PREFETCH_CONFIG1, prefetch_config1);
> +	} else {
> +		/* Set the amount of bytes to be prefetched */
> +		gpmc_write_reg(GPMC_PREFETCH_CONFIG2, u32_count);
> +
> +		/* Set dma/mpu mode, the prefech read and enable the engine
> +		 * Set which cs is using the prefetch
> +		 */
> +		prefetch_config1 = gpmc_read_reg(GPMC_PREFETCH_CONFIG1);
> +		prefetch_config1 |= (((cs << CS_NUM_SHIFT) |
> +					(dma_mode << DMA_MPU_MODE) |
> +					(1 << ENABLE_PREFETCH)) & ~0x1);
> +		gpmc_write_reg(GPMC_PREFETCH_CONFIG1, prefetch_config1);
> +	}
> +	/*  Start the prefetch engine */
> +	gpmc_write_reg(GPMC_PREFETCH_CONTROL, 0x1);
> +}
> +EXPORT_SYMBOL(gpmc_prefetch_start);
> +
> +/**
> + * gpmc_prefetch_stop - disables and stops the prefetch engine
> + */
> +void gpmc_prefetch_stop(void)
> +{
> +	uint32_t prefetch_config1;
> +	/* stop the PFPW engine */
> +	gpmc_write_reg(GPMC_PREFETCH_CONTROL, 0x0);
> +
> +	/* Disable the PFPW engine */
> +	prefetch_config1 = gpmc_read_reg(GPMC_PREFETCH_CONFIG1);
> +	prefetch_config1 &= ~((0x07 << CS_NUM_SHIFT) |
> +				(1 << ENABLE_PREFETCH) |
> +					(1 << DMA_MPU_MODE) | 0x1);
> +	gpmc_write_reg(GPMC_PREFETCH_CONFIG1, prefetch_config1);
> +}
> +EXPORT_SYMBOL(gpmc_prefetch_stop);
> +
> +/**
> + * gpmc_prefetch_status - reads prefetch status of engine
> + */
> +int  gpmc_prefetch_status(void)
> +{
> +	return gpmc_read_reg(GPMC_PREFETCH_STATUS);
> +}
> +EXPORT_SYMBOL(gpmc_prefetch_status);
> +#else
> +int  gpmc_prefetch_status(void)
> +{
> +	return 0;
> +}
> +void gpmc_prefetch_stop(void)
> +{
> +}
> +void gpmc_prefetch_start(int cs, int dma_mode,
> +				unsigned int u32_count, int is_write)
> +{
> +}
> +#endif
> +
>  static void __init gpmc_mem_init(void)
>  {
>  	int cs;
> @@ -447,5 +546,8 @@ void __init gpmc_init(void)
>  	l |= (0x02 << 3) | (1 << 0);
>  	gpmc_write_reg(GPMC_SYSCONFIG, l);
> 
> +#ifdef CONFIG_MTD_NAND_OMAP_PREFETCH
> +	gpmc_prefetch_init();
> +#endif
>  	gpmc_mem_init();
>  }
> Index: mtd-2.6/arch/arm/plat-omap/include/mach/gpmc.h
> ===================================================================
> --- mtd-2.6.orig/arch/arm/plat-omap/include/mach/gpmc.h
> +++ mtd-2.6/arch/arm/plat-omap/include/mach/gpmc.h
> @@ -103,6 +103,10 @@ extern int gpmc_cs_request(int cs, unsig
>  extern void gpmc_cs_free(int cs);
>  extern int gpmc_cs_set_reserved(int cs, int reserved);
>  extern int gpmc_cs_reserved(int cs);
> +extern void gpmc_prefetch_start(int cs, int dma_mode,
> +					unsigned int u32_count, int is_write);
> +extern void gpmc_prefetch_stop(void);
> +extern int  gpmc_prefetch_status(void);
>  extern void __init gpmc_init(void);
> 
>  #endif
> Index: mtd-2.6/drivers/mtd/nand/Kconfig
> ===================================================================
> --- mtd-2.6.orig/drivers/mtd/nand/Kconfig
> +++ mtd-2.6/drivers/mtd/nand/Kconfig
> @@ -80,6 +80,23 @@ config MTD_NAND_OMAP2
>  	help
>            Support for NAND flash on Texas Instruments OMAP2 and OMAP3 platforms.
> 
> +config MTD_NAND_OMAP_PREFETCH
> +	bool "GPMC prefetch support for NAND Flash device"
> +	depends on MTD_NAND && MTD_NAND_OMAP2
> +	default y
> +	help
> +	 The NAND device can be accessed for Read/Write using GPMC PREFETCH engine
> +	 to improve the performance.
> +
> +config MTD_NAND_OMAP_PREFETCH_DMA
> +	depends on MTD_NAND_OMAP_PREFETCH
> +	bool "DMA mode"
> +	default n
> +	help
> +	 The GPMC PREFETCH engine can be configured eigther in MPU interrupt mode
> +	 or in DMA interrupt mode.
> +	 Say y for DMA mode or MPU mode will be used
> +
>  config MTD_NAND_TS7250
>  	tristate "NAND Flash device on TS-7250 board"
>  	depends on MACH_TS72XX
> Index: mtd-2.6/drivers/mtd/nand/omap2.c
> ===================================================================
> --- mtd-2.6.orig/drivers/mtd/nand/omap2.c
> +++ mtd-2.6/drivers/mtd/nand/omap2.c
> @@ -16,8 +16,7 @@
>  #include <linux/mtd/partitions.h>
>  #include <linux/io.h>
> 
> -#include <asm/dma.h>
> -
> +#include <mach/dma.h>
>  #include <mach/gpmc.h>
>  #include <mach/nand.h>
> 
> @@ -110,6 +109,27 @@
>  static const char *part_probes[] = { "cmdlinepart", NULL };
>  #endif
> 
> +#ifdef CONFIG_MTD_NAND_OMAP_PREFETCH
> +static int use_prefetch = 1;
> +
> +/* "modprobe ... use_prefetch=0" etc */
> +module_param(use_prefetch, bool, 0);
> +MODULE_PARM_DESC(use_prefetch, "enable/disable use of PREFETCH");
> +
> +#ifdef CONFIG_MTD_NAND_OMAP_PREFETCH_DMA
> +static int use_dma = 1;
> +
> +/* "modprobe ... use_dma=0" etc */
> +module_param(use_dma, bool, 0);
> +MODULE_PARM_DESC(use_dma, "enable/disable use of DMA");
> +#else
> +const int use_dma;
> +#endif
> +#else
> +const int use_prefetch;
> +const int use_dma;
> +#endif
> +
>  struct omap_nand_info {
>  	struct nand_hw_control		controller;
>  	struct omap_nand_platform_data	*pdata;
> @@ -122,6 +142,9 @@ struct omap_nand_info {
>  	unsigned long			phys_base;
>  	void __iomem			*gpmc_cs_baseaddr;
>  	void __iomem			*gpmc_baseaddr;
> +	void __iomem			*nand_pref_fifo_add;
> +	struct completion		comp;
> +	int				dma_ch;
>  };
> 
>  /**
> @@ -187,6 +210,40 @@ static void omap_hwcontrol(struct mtd_in
>  }
> 
>  /**
> + * omap_read_buf8 - read data from NAND controller into buffer
> + * @mtd: MTD device structure
> + * @buf: buffer to store date
> + * @len: number of bytes to read
> + */
> +static void omap_read_buf8(struct mtd_info *mtd, u_char *buf, int len)
> +{
> +	struct nand_chip *nand = mtd->priv;
> +	u_char *p = (u_char *)buf;
> +
> +	while (len--)
> +		*p++ = __raw_readb(nand->IO_ADDR_R);
> +}
> +
> +/**
> + * omap_write_buf8 - write buffer to NAND controller
> + * @mtd: MTD device structure
> + * @buf: data buffer
> + * @len: number of bytes to write
> + */
> +static void omap_write_buf8(struct mtd_info *mtd, const u_char *buf, int len)
> +{
> +	struct omap_nand_info *info = container_of(mtd,
> +						struct omap_nand_info, mtd);
> +	u_char *p = (u_char *)buf;
> +
> +	while (len--) {
> +		writeb(*p++, info->nand.IO_ADDR_W);
> +		while (GPMC_BUF_EMPTY == (readl(info->gpmc_baseaddr +
> +						GPMC_STATUS) & GPMC_BUF_FULL));
> +	}
> +}
> +
> +/**
>   * omap_read_buf16 - read data from NAND controller into buffer
>   * @mtd: MTD device structure
>   * @buf: buffer to store date
> @@ -222,6 +279,205 @@ static void omap_write_buf16(struct mtd_
>  			;
>  	}
>  }
> +
> +#ifdef CONFIG_MTD_NAND_OMAP_PREFETCH_DMA
> +/**
> + * omap_nand_dma_cb: callback on the completion of dma transfer
> + * @lch: logical channel
> + * @ch_satuts: channel status
> + * @data: pointer to completion data structure
> + */
> +static void omap_nand_dma_cb(int lch, u16 ch_status, void *data)
> +{
> +	complete((struct completion *) data);
> +}
> +
> +/**
> + * omap_nand_dma_transfer: configer and start dma transfer
> + * @mtd: MTD device structure
> + * @addr: virtual address in RAM of source/destination
> + * @len: number of data bytes to be transferred
> + * @is_write: flag for read/write operation
> + */
> +static inline int omap_nand_dma_transfer(struct mtd_info *mtd, void *addr,
> +					unsigned int len, int is_write)
> +{
> +	struct omap_nand_info *info = container_of(mtd,
> +					struct omap_nand_info, mtd);
> +	uint32_t prefetch_status = 0;
> +	enum dma_data_direction dir = is_write ? DMA_TO_DEVICE :
> +							DMA_FROM_DEVICE;
> +	dma_addr_t dma_addr;
> +
> +	/* The fifo depth is 64 bytes. We have a sync at each frame and frame
> +	 * length is 64 bytes.
> +	 */
> +	int buf_len = len/64;
> +
> +	if (addr >= high_memory) {
> +		struct page *p1;
> +
> +		if (((size_t)addr & PAGE_MASK) !=
> +			((size_t)(addr + len - 1) & PAGE_MASK))
> +			goto out_copy;
> +		p1 = vmalloc_to_page(addr);
> +		if (!p1)
> +			goto out_copy;
> +		addr = page_address(p1) + ((size_t)addr & ~PAGE_MASK);
> +	}
> +
> +	dma_addr = dma_map_single(&info->pdev->dev, addr, len, dir);
> +	if (dma_mapping_error(&info->pdev->dev, dma_addr)) {
> +		dev_err(&info->pdev->dev,
> +			"Couldn't DMA map a %d byte buffer\n", len);
> +		goto out_copy;
> +	}
> +
> +	if (is_write) {
> +	    omap_set_dma_dest_params(info->dma_ch, 0, OMAP_DMA_AMODE_CONSTANT,
> +						info->phys_base, 0, 0);
> +	    omap_set_dma_dest_burst_mode(info->dma_ch, OMAP_DMA_DATA_BURST_16);
> +	    omap_set_dma_src_params(info->dma_ch, 0, OMAP_DMA_AMODE_POST_INC,
> +							dma_addr, 0, 0);
> +	    omap_set_dma_src_burst_mode(info->dma_ch, OMAP_DMA_DATA_BURST_16);
> +	    omap_set_dma_transfer_params(info->dma_ch, OMAP_DMA_DATA_TYPE_S32,
> +					0x10, buf_len, OMAP_DMA_SYNC_FRAME,
> +					OMAP24XX_DMA_GPMC, OMAP_DMA_DST_SYNC);
> +	} else {
> +	    omap_set_dma_src_params(info->dma_ch, 0, OMAP_DMA_AMODE_CONSTANT,
> +						info->phys_base, 0, 0);
> +	    omap_set_dma_src_burst_mode(info->dma_ch, OMAP_DMA_DATA_BURST_16);
> +	    omap_set_dma_dest_params(info->dma_ch, 0, OMAP_DMA_AMODE_POST_INC,
> +							dma_addr, 0, 0);
> +	    omap_set_dma_dest_burst_mode(info->dma_ch, OMAP_DMA_DATA_BURST_16);
> +	    omap_set_dma_transfer_params(info->dma_ch, OMAP_DMA_DATA_TYPE_S32,
> +					0x10, buf_len, OMAP_DMA_SYNC_FRAME,
> +					OMAP24XX_DMA_GPMC, OMAP_DMA_SRC_SYNC);
> +	}
> +	/*  configure and start prefetch transfer */
> +	gpmc_prefetch_start(info->gpmc_cs, 0x1, len, is_write);
> +	init_completion(&info->comp);
> +
> +	omap_start_dma(info->dma_ch);
> +
> +	/* setup and start DMA using dma_addr */
> +	wait_for_completion(&info->comp);
> +
> +	while (0x3fff & (prefetch_status = gpmc_prefetch_status()))
> +		;
> +	/* disable and stop the PFPW engine */
> +	gpmc_prefetch_stop();
> +
> +	dma_unmap_single(&info->pdev->dev, dma_addr, len, dir);
> +	return 0;
> +
> +out_copy:
> +	if (info->nand.options & NAND_BUSWIDTH_16)
> +		is_write == 0 ? omap_read_buf16(mtd, (u_char *) addr, len)
> +			: omap_write_buf16(mtd, (u_char *) addr, len);
> +	else
> +		is_write == 0 ? omap_read_buf8(mtd, (u_char *) addr, len)
> +			: omap_write_buf8(mtd, (u_char *) addr, len);
> +	return 0;
> +}
> +#else
> +static void omap_nand_dma_cb(int lch, u16 ch_status, void *data)
> +{
> +}
> +static inline int omap_nand_dma_transfer(struct mtd_info *mtd, void *addr,
> +					unsigned int len, int is_write)
> +{
> +	return 0;
> +}
> +#endif
> +
> +/**
> + * omap_read_buf_pref - read data from NAND controller into buffer
> + * @mtd: MTD device structure
> + * @buf: buffer to store date
> + * @len: number of bytes to read
> + */
> +static void omap_read_buf_pref(struct mtd_info *mtd, u_char *buf, int len)
> +{
> +	struct omap_nand_info *info = container_of(mtd,
> +						struct omap_nand_info, mtd);
> +	uint32_t prefetch_status = 0, read_count = 0;
> +	u32 *p = (u32 *)buf;
> +
> +	if ((use_dma && len <= mtd->oobsize) || (!use_dma)) {
> +
> +		/* take care of subpage reads */
> +		for (; len % 4 != 0; ) {
> +			*buf++ = __raw_readb(info->nand.IO_ADDR_R);
> +			len--;
> +		}
> +		p = (u32 *) buf;
> +
> +		/* configure and start prefetch transfer */
> +		gpmc_prefetch_start(info->gpmc_cs, 0x0, len, 0x0);
> +
> +		do {
> +			prefetch_status = gpmc_prefetch_status();
> +			read_count = ((prefetch_status >> 24) & 0x7F) >> 2;
> +			__raw_readsl(info->nand_pref_fifo_add, p,
> +							read_count);
> +			p += read_count;
> +			len -= read_count << 2;
> +		} while (len);
> +
> +		/* disable and stop the PFPW engine */
> +		gpmc_prefetch_stop();
> +	} else if (use_dma) {
> +		if (info->dma_ch >= 0)
> +			/* start transfer in DMA mode */
> +			omap_nand_dma_transfer(mtd, p, len, 0x0);
> +	}
> +}
> +
> +/**
> + * omap_write_buf_pref - write buffer to NAND controller
> + * @mtd: MTD device structure
> + * @buf: data buffer
> + * @len: number of bytes to write
> + */
> +static void omap_write_buf_pref(struct mtd_info *mtd,
> +					const u_char *buf, int len)
> +{
> +	struct omap_nand_info *info = container_of(mtd,
> +						struct omap_nand_info, mtd);
> +	uint32_t prefetch_status = 0, write_count = 0;
> +	int i = 0;
> +	u16 *p = (u16 *) buf;
> +
> +	if ((use_dma && len <= mtd->oobsize) || (!use_dma)) {
> +
> +		/* take care of subpage writes */
> +		if (len % 2 != 0) {
> +			writeb(*buf, info->nand.IO_ADDR_R);
> +			p = (u16 *)(buf + 1);
> +			len--;
> +		}
> +
> +		/*  configure and start prefetch transfer */
> +		gpmc_prefetch_start(info->gpmc_cs, 0x0, len, 0x1);
> +
> +		prefetch_status = gpmc_prefetch_status();
> +		while (prefetch_status & 0x3FFF) {
> +			write_count = ((prefetch_status >> 24) & 0x7F) >> 1;
> +			for (i = 0; (i < write_count) && len; i++, len -= 2)
> +				__raw_writew(*p++, info->nand_pref_fifo_add);
> +				prefetch_status = gpmc_prefetch_status();
> +		}
> +
> +		/* disable and stop the PFPW engine */
> +		gpmc_prefetch_stop();
> +	} else if (use_dma) {
> +		if (info->dma_ch >= 0)
> +			/* start transfer in DMA mode */
> +			omap_nand_dma_transfer(mtd, p, len, 0x1);
> +	}
> +}
> +
>  /**
>   * omap_verify_buf - Verify chip data against buffer
>   * @mtd: MTD device structure
> @@ -655,17 +911,25 @@ static int __devinit omap_nand_probe(str
>  		err = -ENOMEM;
>  		goto out_release_mem_region;
>  	}
> +
> +	if (use_prefetch) {
> +		/* copy the virtual address of nand base for fifo access */
> +		info->nand_pref_fifo_add = info->nand.IO_ADDR_R;
> +		if (use_dma) {
> +			err = omap_request_dma(OMAP24XX_DMA_GPMC, "NAND",
> +				omap_nand_dma_cb, &info->comp, &info->dma_ch);
> +			if (err < 0) {
> +				info->dma_ch = -1;
> +				printk(KERN_WARNING "DMA request failed."
> +					" Non-dma data transfer mode\n");
> +			}
> +		}
> +	}
>  	info->nand.controller = &info->controller;
> 
>  	info->nand.IO_ADDR_W = info->nand.IO_ADDR_R;
>  	info->nand.cmd_ctrl  = omap_hwcontrol;
> 
> -	/* REVISIT:  only supports 16-bit NAND flash */
> -
> -	info->nand.read_buf   = omap_read_buf16;
> -	info->nand.write_buf  = omap_write_buf16;
> -	info->nand.verify_buf = omap_verify_buf;
> -
>  	/*
>  	 * If RDY/BSY line is connected to OMAP then use the omap ready
>  	 * funcrtion and the generic nand_wait function which reads the status
> @@ -686,6 +950,20 @@ static int __devinit omap_nand_probe(str
>  								== 0x1000)
>  		info->nand.options  |= NAND_BUSWIDTH_16;
> 
> +	if (use_prefetch) {
> +		info->nand.read_buf   = omap_read_buf_pref;
> +		info->nand.write_buf  = omap_write_buf_pref;
> +	} else {
> +		if (info->nand.options & NAND_BUSWIDTH_16) {
> +			info->nand.read_buf   = omap_read_buf16;
> +			info->nand.write_buf  = omap_write_buf16;
> +		} else {
> +			info->nand.read_buf   = omap_read_buf8;
> +			info->nand.write_buf  = omap_write_buf8;
> +		}
> +	}
> +	info->nand.verify_buf = omap_verify_buf;
> +
>  #ifdef CONFIG_MTD_NAND_OMAP_HWECC
>  	info->nand.ecc.bytes		= 3;
>  	info->nand.ecc.size		= 512;
> @@ -741,9 +1019,12 @@ static int omap_nand_remove(struct platf
>  	struct omap_nand_info *info = mtd->priv;
> 
>  	platform_set_drvdata(pdev, NULL);
> +	if (use_dma)
> +		omap_free_dma(info->dma_ch);
> +
>  	/* Release NAND device, its internal structures and partitions */
>  	nand_release(&info->mtd);
> -	iounmap(info->nand.IO_ADDR_R);
> +	iounmap(info->nand_pref_fifo_add);
>  	kfree(&info->mtd);
>  	return 0;
>  }
> @@ -760,6 +1041,15 @@ static struct platform_driver omap_nand_
>  static int __init omap_nand_init(void)
>  {
>  	printk(KERN_INFO "%s driver initializing\n", DRIVER_NAME);
> +
> +	/* This check is required if driver is being
> +	 * loaded run time as a module
> +	 */
> +	if ((1 == use_dma) && (0 == use_prefetch)) {
> +		printk(KERN_INFO"Wrong parameters: 'use_dma' can not be 1 "
> +				"without use_prefetch'. Prefetch will not be"
> +				" used in either mode (mpu or dma)\n");
> +	}
>  	return platform_driver_register(&omap_nand_driver);
>  }
> 
> 
> 
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