[U-Boot] [PATCH 1/4] Optimized nand_read_buf for kirkwood

[Scott Wood <scottwood@freescale.com>]

On 11/26/2012 04:33:08 AM, Phil Sutter wrote:
> The basic idea is taken from the linux-kernel, but further optimized.
> 
> First align the buffer to 8 bytes, then use ldrd/strd to read and  
> store
> in 8 byte quantities, then do the final bytes.
> 
> Tested using: 'date ; nand read.raw 0xE00000 0x0 0x10000 ; date'.
> Without this patch, NAND read of 132MB took 49s (~2.69MB/s). With this
> patch in place, reading the same amount of data was done in 27s
> (~4.89MB/s). So read performance is increased by ~80%!
> 
> Signed-off-by: Nico Erfurth <ne@erfurth.eu>
> Tested-by: Phil Sutter <phil.sutter@viprinet.com>
> Cc: Prafulla Wadaskar <prafulla@marvell.com>
> ---
>  drivers/mtd/nand/kirkwood_nand.c |   29 +++++++++++++++++++++++++++++
>  1 files changed, 29 insertions(+), 0 deletions(-)
> 
> diff --git a/drivers/mtd/nand/kirkwood_nand.c  
> b/drivers/mtd/nand/kirkwood_nand.c
> index bdab5aa..e04a59f 100644
> --- a/drivers/mtd/nand/kirkwood_nand.c
> +++ b/drivers/mtd/nand/kirkwood_nand.c
> @@ -38,6 +38,34 @@ struct kwnandf_registers {
>  static struct kwnandf_registers *nf_reg =
>  	(struct kwnandf_registers *)KW_NANDF_BASE;
> 
> +
> +/* The basic idea is stolen from the linux kernel, but the inner  
> loop is optimized a bit more */
> +static void kw_nand_read_buf(struct mtd_info *mtd, uint8_t *buf, int  
> len)
> +{
> +	struct nand_chip *chip = mtd->priv;
> +
> +	while (len && (unsigned long)buf & 7)
> +	{

Brace goes on the previous line.

> +		*buf++ = readb(chip->IO_ADDR_R);
> +		len--;
> +	};
> +
> +	asm volatile (
> +		".LFlashLoop:\n"
> +		"  subs\t%0, #8\n"
> +		"  ldrpld\tr2, [%2]\n" // Read 2 words
> +		"  strpld\tr2, [%1], #8\n" // Read 2 words
> +		"  bpl\t.LFlashLoop\n" // This results in one  
> additional loop if len%8 <> 0
> +		"  addne\t%0, #8\n"
> +		: "+&r" (len), "+&r" (buf)
> +		: "r" (chip->IO_ADDR_R)
> +		: "r2", "r3", "memory", "cc"
> +	);

Use a real tab (or a space) rather than \t (which only helps  
readability in the asm output, rather than the C source that people  
actually look at).

Should probably use a numeric label to avoid any possibility of  
conflict.

Would this make more sense as a more generic optimized memcpy_fromio()  
or similar?

-Scott