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Message-ID: <4D34A37E.1060300@bluewatersys.com>
Date: Tue, 18 Jan 2011 09:15:58 +1300
From: Ryan Mallon <ryan@...ewatersys.com>
To: Hong Xu <hong.xu@...el.com>
CC: linux-mtd@...ts.infradead.org,
linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
jamie@...ieiles.com, jacmet@...site.dk, nicolas.ferre@...el.com
Subject: Re: [PATCH] MTD: atmel_nand: Add DMA support to access Nandflash
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@...el.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);
>
--
Bluewater Systems Ltd - ARM Technology Solution Centre
Ryan Mallon 5 Amuri Park, 404 Barbadoes St
ryan@...ewatersys.com PO Box 13 889, Christchurch 8013
http://www.bluewatersys.com New Zealand
Phone: +64 3 3779127 Freecall: Australia 1800 148 751
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