[U-Boot] [PATCH] orion5x: optimize window size computation

[Prafulla Wadaskar]

> -----Original Message-----
> From: u-boot-bounces at lists.denx.de 
> [mailto:u-boot-bounces at lists.denx.de] On Behalf Of Albert Aribaud
> Sent: Tuesday, October 05, 2010 3:52 AM
> To: u-boot at lists.denx.de
> Subject: [U-Boot] [PATCH] orion5x: optimize window size computation
> 
> 
> Signed-off-by: Chris Moore <moore at free.fr>
> ---
> 
> This is a simple optimization of the orion5x window size
> computation. This code was contributed by Chris Moore so
> I put his Signed-off-by rather than mine.

This is wrong, you should be singed-off since you are posting and Chris can be contributor
Or let him post the patch.

> 
> See <http://www.mail-archive.com/u-boot@lists.denx.de/msg37075.html>
> 
>  arch/arm/cpu/arm926ejs/orion5x/cpu.c |   30 
> ++++++++++++++++++++----------
>  1 files changed, 20 insertions(+), 10 deletions(-)
> 
> diff --git a/arch/arm/cpu/arm926ejs/orion5x/cpu.c 
> b/arch/arm/cpu/arm926ejs/orion5x/cpu.c
> index c36d7bf..5c443fe 100644
> --- a/arch/arm/cpu/arm926ejs/orion5x/cpu.c
> +++ b/arch/arm/cpu/arm926ejs/orion5x/cpu.c
> @@ -48,24 +48,34 @@ void reset_cpu(unsigned long ignored)
>  }
>  
>  /*
> - * Window Size
> + * Compute Window Size field value from size expressed in bytes
>   * Used with the Base register to set the address window 
> size and location.
>   * Must be programmed from LSB to MSB as sequence of ones followed by
>   * sequence of zeros. The number of ones specifies the size 
> of the window in
>   * 64 KByte granularity (e.g., a value of 0x00FF specifies 
> 256 = 16 MByte).
> - * NOTE: A value of 0x0 specifies 64-KByte size.
> + * NOTES:
> + * 1) A sizeval equal to 0x0 specifies 4 TB.
> + * 2) A return value of 0x0 specifies 64 KB.
>   */
>  unsigned int orion5x_winctrl_calcsize(unsigned int sizeval)
>  {
> -	int i;
> -	unsigned int j = 0;
> -	u32 val = sizeval >> 1;
> +	/*
> +	 * Calculate the number of 64 KiB blocks needed minus 
> one (rounding up).
> +	 * For sizeval > 0 this is equivalent to:
> +	 * sizeval = (u32) ceil((double) sizeval / 65536.0) - 1
> +	 */
> +	sizeval = (sizeval - 1) >> 16;
>  
> -	for (i = 0; val >= 0x10000; i++) {
> -		j |= (1 << i);
> -		val = val >> 1;
> -	}
> -	return 0x0000ffff & j;
> +	/*
> +	 * Propagate 'one' bits to the right by 'oring' them.
> +	 * We need only treat bits 15-0.
> +	 */
> +	sizeval |= sizeval >> 1;  /* 'Or' bit 15 onto bit 14 */
> +	sizeval |= sizeval >> 2;  /* 'Or' bits 15-14 onto bits 13-12 */
> +	sizeval |= sizeval >> 4;  /* 'Or' bits 15-12 onto bits 11-8 */
> +	sizeval |= sizeval >> 8;  /* 'Or' bits 15-8 onto bits 7-0*/
> +
> +	return sizeval;

BTW: How much this saves on size?

Regards..
Prafulla ..