Re: [PATCH] MTD: atmel_nand: Add DMA support to access Nandflash

[Ryan Mallon <ryan@bluewatersys.com>]

On 01/17/2011 08:20 PM, Hong Xu wrote:
> Some SAM9 chips have the ability to perform DMA between CPU and SMC controller.
> This patch adds DMA support for SAM9RL, SAM9G45, SSAM9G46,AM9M10, SAM9M11.

Hi Hong,

A few comments below.

~Ryan

> Signed-off-by: Hong Xu <hong.xu@atmel.com>
> ---
>  drivers/mtd/nand/atmel_nand.c |  160 ++++++++++++++++++++++++++++++++++++++++-
>  1 files changed, 158 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/mtd/nand/atmel_nand.c b/drivers/mtd/nand/atmel_nand.c
> index ccce0f0..ba59913 100644
> --- a/drivers/mtd/nand/atmel_nand.c
> +++ b/drivers/mtd/nand/atmel_nand.c
> @@ -48,6 +48,9 @@
>  #define no_ecc		0
>  #endif
>  
> +static int use_dma = 1;
> +module_param(use_dma, int, 0);
> +
>  static int on_flash_bbt = 0;
>  module_param(on_flash_bbt, int, 0);
>  
> @@ -89,11 +92,21 @@ struct atmel_nand_host {
>  	struct nand_chip	nand_chip;
>  	struct mtd_info		mtd;
>  	void __iomem		*io_base;
> +	dma_addr_t		io_phys;
>  	struct atmel_nand_data	*board;
>  	struct device		*dev;
>  	void __iomem		*ecc;
> +
> +	int dma_ready;

The name dma_ready implies that it is used as a flag to indicate when
the dma engine is ready to do a transfer, but you are using it to
indicate that the host supports dma. Would be more clear to call it
'use_dma'.

> +	struct completion comp;
> +	struct dma_chan *dma_chan;
>  };
>  
> +static int cpu_has_dma(void)
> +{
> +	return cpu_is_at91sam9rl() || cpu_is_at91sam9g45();
> +}
> +
>  /*
>   * Enable NAND.
>   */
> @@ -150,7 +163,7 @@ static int atmel_nand_device_ready(struct mtd_info *mtd)
>  /*
>   * Minimal-overhead PIO for data access.
>   */
> -static void atmel_read_buf(struct mtd_info *mtd, u8 *buf, int len)
> +static void atmel_read_buf8(struct mtd_info *mtd, u8 *buf, int len)
>  {
>  	struct nand_chip	*nand_chip = mtd->priv;
>  
> @@ -164,7 +177,7 @@ static void atmel_read_buf16(struct mtd_info *mtd, u8 *buf, int len)
>  	__raw_readsw(nand_chip->IO_ADDR_R, buf, len / 2);
>  }
>  
> -static void atmel_write_buf(struct mtd_info *mtd, const u8 *buf, int len)
> +static void atmel_write_buf8(struct mtd_info *mtd, const u8 *buf, int len)
>  {
>  	struct nand_chip	*nand_chip = mtd->priv;
>  
> @@ -178,6 +191,123 @@ static void atmel_write_buf16(struct mtd_info *mtd, const u8 *buf, int len)
>  	__raw_writesw(nand_chip->IO_ADDR_W, buf, len / 2);
>  }
>  
> +static void dma_complete_func(void *completion)
> +{
> +	complete(completion);
> +}

You can make the function below a bit more concise:

> +static int atmel_nand_dma_op(struct mtd_info *mtd, void *buf, int len,
> +			       int is_read)
> +{
> +	struct dma_device *dma_dev;
> +	enum dma_ctrl_flags flags;
> +	dma_addr_t dma_src_addr, dma_dst_addr, phys_addr;
> +	struct dma_async_tx_descriptor *tx = NULL;
> +	dma_cookie_t cookie;
> +	struct nand_chip *chip = mtd->priv;
> +	struct atmel_nand_host *host = chip->priv;
> +	void *p = buf;

	int dir = is_read ? DMA_FROM_DEVICE : DMA_TO_DEVICE;

> +
> +	if (buf >= high_memory) {
> +		struct page *pg;
> +
> +		if (((size_t)buf & PAGE_MASK) !=
> +		    ((size_t)(buf + len - 1) & PAGE_MASK))

Print a warning here? The other failures all have warning messages.

> +			goto err_dma;
> +
> +		pg = vmalloc_to_page(buf);
> +		if (pg == 0)
> +			goto err_dma;
> +		p = page_address(pg) + ((size_t)buf & ~PAGE_MASK);
> +	}
> +
> +	dma_dev = host->dma_chan->device;
> +
> +	flags = DMA_CTRL_ACK | DMA_COMPL_SKIP_DEST_UNMAP | DMA_PREP_INTERRUPT |
> +			DMA_COMPL_SKIP_SRC_UNMAP;
> +
> +	if (is_read)
> +		phys_addr = dma_map_single(dma_dev->dev, p, len,
> +					   DMA_FROM_DEVICE);
> +	else
> +		phys_addr = dma_map_single(dma_dev->dev, p, len,
> +					   DMA_TO_DEVICE);

	phys_addr = dma_map_single(dma_dev->dev, p, len, dir);

> +	if (dma_mapping_error(dma_dev->dev, phys_addr)) {
> +		dev_err(host->dev, "Failed to dma_map_single\n");
> +		goto err_dma;
> +	}
> +
> +	if (is_read) {
> +		dma_src_addr = host->io_phys;
> +		dma_dst_addr = phys_addr;
> +	} else {
> +		dma_src_addr = phys_addr;
> +		dma_dst_addr = host->io_phys;
> +	}

> +
> +	tx = dma_dev->device_prep_dma_memcpy(host->dma_chan, dma_dst_addr,
> +					     dma_src_addr, len, flags);
> +	if (!tx) {
> +		dev_err(host->dev, "Failed to prepare DMA memcpy\n");
> +		goto err;
> +	}
> +
> +	init_completion(&host->comp);
> +	tx->callback = dma_complete_func;
> +	tx->callback_param = &host->comp;
> +
> +	cookie = tx->tx_submit(tx);
> +	if (dma_submit_error(cookie)) {
> +		dev_err(host->dev, "Failed to do DMA tx_submit\n");
> +		goto err;
> +	}
> +
> +	dma_async_issue_pending(host->dma_chan);
> +
> +	wait_for_completion(&host->comp);

	dma_unmap_single(dma_dev->dev, phys_addr, len, dir);

> +	return 0;
> +
> +err:
> +	if (is_read)
> +		dma_unmap_single(dma_dev->dev, phys_addr, len, DMA_FROM_DEVICE);
> +	else
> +		dma_unmap_single(dma_dev->dev, phys_addr, len, DMA_TO_DEVICE);

	dma_unmap_single(dma_dev->dev, phys_addr, len, dir);

> +err_dma:
> +	/* Fall back to CPU I/O */
> +	return -1;

Return a proper error code.

> +}
> +
> +static void atmel_read_buf(struct mtd_info *mtd, u8 *buf, int len)
> +{
> +	struct nand_chip *chip = mtd->priv;
> +	struct atmel_nand_host *host = chip->priv;
> +
> +	if (host->dma_ready && len >= mtd->oobsize)
> +		if (atmel_nand_dma_op(mtd, buf, len, 1) == 0)
> +			return;
> +
> +	if (host->board->bus_width_16)
> +		atmel_read_buf16(mtd, buf, len);
> +	else
> +		atmel_read_buf8(mtd, buf, len);
> +}
> +
> +static void atmel_write_buf(struct mtd_info *mtd, const u8 *buf, int len)
> +{
> +	struct nand_chip *chip = mtd->priv;
> +	struct atmel_nand_host *host = chip->priv;
> +
> +	if (host->dma_ready && len >= mtd->oobsize)
> +		if (atmel_nand_dma_op(mtd, (void *)buf, len, 0) == 0)
> +			return;
> +
> +	if (host->board->bus_width_16)
> +		atmel_write_buf16(mtd, buf, len);
> +	else
> +		atmel_write_buf8(mtd, buf, len);
> +}

In atmel_nand_probe you have the following:

    if (host->board->bus_width_16) {    /* 16-bit bus width */
        nand_chip->options |= NAND_BUSWIDTH_16;
        nand_chip->read_buf = atmel_read_buf16;
        nand_chip->write_buf = atmel_write_buf16;
    } else {
        nand_chip->read_buf = atmel_read_buf;
        nand_chip->write_buf = atmel_write_buf;
    }

So DMA is not supported when the bus width is 16? Possibly you just want
to use atmel_[read|write]_buf in all cases?

> +
>  /*
>   * Calculate HW ECC
>   *
> @@ -398,6 +528,8 @@ static int __init atmel_nand_probe(struct platform_device *pdev)
>  		return -ENOMEM;
>  	}
>  
> +	host->io_phys = (dma_addr_t)mem->start;
> +

host->io_phys can be replaced by a stack variable in atmel_nand_probe,
or just (dma_addr_t)mem->start, since it is only used in this function.

>  	host->io_base = ioremap(mem->start, mem->end - mem->start + 1);
>  	if (host->io_base == NULL) {
>  		printk(KERN_ERR "atmel_nand: ioremap failed\n");
> @@ -516,6 +648,24 @@ static int __init atmel_nand_probe(struct platform_device *pdev)
>  		}
>  	}
>  
> +	if (cpu_has_dma() && use_dma) {
> +		dma_cap_mask_t mask;
> +
> +		dma_cap_zero(mask);
> +		dma_cap_set(DMA_MEMCPY, mask);
> +		host->dma_chan = dma_request_channel(mask, 0, NULL);
> +

Nitpick: don't have blank lines between a function call and its error check.

> +		if (!host->dma_chan) {
> +			dev_err(host->dev, "Failed to request DMA channel\n");
> +			host->dma_ready = 0;
> +		} else
> +			host->dma_ready = 1;

Nitpick: the else should have braces since the if statement does.

> +	}
> +	if (host->dma_ready)
> +		dev_info(host->dev, "Using DMA for NAND access.\n");
> +	else
> +		dev_info(host->dev, "No DMA support for NAND access.\n");
> +
>  	/* second phase scan */
>  	if (nand_scan_tail(mtd)) {
>  		res = -ENXIO;
> @@ -555,6 +705,8 @@ err_scan_ident:
>  err_no_card:
>  	atmel_nand_disable(host);
>  	platform_set_drvdata(pdev, NULL);
> +	if (host->dma_chan)
> +		dma_release_channel(host->dma_chan);
>  	if (host->ecc)
>  		iounmap(host->ecc);
>  err_ecc_ioremap:
> @@ -578,6 +730,10 @@ static int __exit atmel_nand_remove(struct platform_device *pdev)
>  
>  	if (host->ecc)
>  		iounmap(host->ecc);
> +
> +	if (host->dma_chan)
> +		dma_release_channel(host->dma_chan);
> +
>  	iounmap(host->io_base);
>  	kfree(host);
>  


-- 
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