[U-Boot] [PATCH V2] orion5x: optimize window size computation

[U-Boot] [PATCH V2] orion5x: optimize window size computation

[Albert Aribaud]

Signed-off-by: Chris Moore <moore@free.fr>
Signed-off-by: Albert Aribaud <albert.aribaud@free.fr>
---
V1	Initial submission
V2	Double Signed-off-by as requested

 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 260f88b..a49d926 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;
-
-	for (i = 0; val >= 0x10000; i++) {
-		j |= (1 << i);
-		val = val >> 1;
-	}
-	return 0x0000ffff & j;
+	/*
+	 * 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;
+
+	/*
+	 * 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;
 }
 
 /*
-- 
1.7.0.4

[U-Boot] [PATCH V2] orion5x: optimize window size computation

[Chris Moore]

  Hi,

Sorry Albert I missed this one last time :(

Le 06/10/2010 16:46, Albert Aribaud a ?crit :
> + * 1) A sizeval equal to 0x0 specifies 4 TB

s/TB/GB/ or maybe even s/TB/GiB/

Question: are MB, GB, ... or MiB, GiB, ... preferred in U-Boot?

I generally try to use the "i" versions where appropriate.
In fact I used a KiB below:

> +	 * Calculate the number of 64 KiB blocks needed minus one (rounding up).

IMHO whatever the choice, it would be preferable to be consistent 
throughout.

Cheers,
Chris

[U-Boot] [PATCH V2] orion5x: optimize window size computation

[Albert ARIBAUD]

Le 06/10/2010 20:01, Chris Moore a ?crit :
> Hi,
>
> Sorry Albert I missed this one last time :(
>
> Le 06/10/2010 16:46, Albert Aribaud a ?crit :
>> + * 1) A sizeval equal to 0x0 specifies 4 TB
>
> s/TB/GB/ or maybe even s/TB/GiB/
>
> Question: are MB, GB, ... or MiB, GiB, ... preferred in U-Boot?

/me slaps himself.

One day, I'll get this one right the first time around, you'll see.

> I generally try to use the "i" versions where appropriate.
> In fact I used a KiB below:
>
>> + * Calculate the number of 64 KiB blocks needed minus one (rounding up).
>
> IMHO whatever the choice, it would be preferable to be consistent
> throughout.

Indeed, and as always, I prefer the les ambiguous choice: 4 TiB it is.

> Cheers,
> Chris

Amicalement,
-- 
Albert.

[U-Boot] [PATCH V2] orion5x: optimize window size computation

[Albert ARIBAUD]

Le 06/10/2010 20:35, Albert ARIBAUD a ?crit :

> Indeed, and as always, I prefer the les ambiguous choice: 4 TiB it is.

Argh!!! 4 *GiB* it is.

Amicalement,
-- 
Albert.

[U-Boot] [PATCH V2] orion5x: optimize window size computation

[Wolfgang Denk]

Dear Chris Moore,

In message <4CACB95F.1000001@free.fr> you wrote:
> 
> Question: are MB, GB, ... or MiB, GiB, ... preferred in U-Boot?

We try to use standard units, i. e. MiB, GiB

> I generally try to use the "i" versions where appropriate.
> In fact I used a KiB below:

ACK.


Best regards,

Wolfgang Denk

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