Re: [PM-WIP-OPP] [PATCH] cleaner ceil function for uv to vsel conversion

[Nishanth Menon <menon.nishanth@gmail.com>]

Romit Dasgupta said the following on 01/12/2010 02:58 AM:
> Kevin Hilman wrote:
>   
>> Romit Dasgupta <romit@ti.com> writes:
>>
>>     
>>> Cleaner ceil function.
>>>       
>> Needs better subject and better changelog.
>>
>> Subject should probably be something like: OMAP: 
>>
>>   [PATCH] OPP: TWL/TPS: optimize uv to vsel function
>>
>> And changelog should describe the motiviation for the patch or a
>> description of the problem you're trying to solve.
>>     
> The description of the problem is "Cleaner ceil function for uv to vsel
> conversion".
>
> I think this patch is simple enough for people on this list to understand the
> optimization. I am sorry I cant be more descriptive.
>
>   
here is a try:
-----

 From patchwork Thu Dec 31 13:29:05 2009
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Subject: [pm-wip-opp] [PATCH] opp: twl/tps: optimize uv to vsel function
Date: Thu, 31 Dec 2009 13:29:05 -0000
From: Dasgupta, Romit <romit@ti.com>
X-Patchwork-Id: 70374


For integer values x and y; int div x / y causes truncation. Current
omap_twl_uv_to_vsel function implements an equivalent of ceil which
is based on an if condition to check truncation and round up.
We can do this in a more optimal manner without the if condition.
The round up is handled by adding the round off factor prior to
truncation as:
(x + (y - 1)) / y

---
Currently putting signed-off in --- section. If Romit is ok, please 
re-send as needed.
Signed-off-by: Dasgupta, Romit <romit@ti.com>

diff --git a/arch/arm/plat-omap/opp_twl_tps.c 
b/arch/arm/plat-omap/opp_twl_tps.c
index e0db39b..43dee2d 100644
--- a/arch/arm/plat-omap/opp_twl_tps.c
+++ b/arch/arm/plat-omap/opp_twl_tps.c
@@ -36,14 +36,7 @@ unsigned long omap_twl_vsel_to_uv(const u8 vsel)
  */
 u8 omap_twl_uv_to_vsel(unsigned long uv)
 {
-    u8 vsel;
+    /* Takes care of precision loss due to integer division */
+    return (((uv + 99) / 100 - 6000) + 124) / 125;
 
-    vsel = ((uv / 100) - 6000) / 125;
-
-    /* round off to higher voltage */
-    /* XXX Surely not the best way to handle this. */
-    if (uv > omap_twl_vsel_to_uv(vsel))
-        vsel++;
-
-    return vsel;
 }