linux-kernel - Re: [PATCH 3/3] power/ds2760_battery: use factor of 20 for rated

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Message-ID: <20100511171924.GA19428@oksana.dev.rtsoft.ru>
Date:	Tue, 11 May 2010 21:19:24 +0400
From:	Anton Vorontsov <cbouatmailru@...il.com>
To:	Daniel Mack <daniel@...aq.de>
Cc:	linux-kernel@...r.kernel.org, Matt Reimer <mreimer@...p.net>,
	Evgeniy Polyakov <zbr@...emap.net>, Tejun Heo <tj@...nel.org>,
	David Woodhouse <dwmw2@...radead.org>,
	Len Brown <len.brown@...el.com>,
	Mark Brown <broonie@...nsource.wolfsonmicro.com>
Subject: Re: [PATCH 3/3] power/ds2760_battery: use factor of 20 for
 rated_capacity

On Tue, May 11, 2010 at 06:38:46PM +0200, Daniel Mack wrote:
> In the ds2760 driver, the currently used factor of 10 to store the rated
> battery capacity internally is not sufficient for batteries > 2.55 Ah,
> as the 8-bit register will overflow for bigger values.
> 
> Change the factor to 20 to broaden that range. Note that due to
> RATED_CAPACITY_FACTOR, the external interface won't change, neither for
> the writeable sysfs entires nor for the kernel rated_capacity module
> parameter.
> 
> Signed-off-by: Daniel Mack <daniel@...aq.de>
> Cc: Anton Vorontsov <avorontsov@...mvista.com>
> Cc: Matt Reimer <mreimer@...p.net>
> Cc: Evgeniy Polyakov <zbr@...emap.net>
> Cc: Tejun Heo <tj@...nel.org>
> Cc: David Woodhouse <dwmw2@...radead.org>
> Cc: Len Brown <len.brown@...el.com>
> Cc: Mark Brown <broonie@...nsource.wolfsonmicro.com>
> ---

Hi Daniel,

Sorry, it took quite a bit to get to your patches.

They look good (as usual), but I have a few concerns.

>  drivers/power/ds2760_battery.c |    2 +-
>  1 files changed, 1 insertions(+), 1 deletions(-)
> 
> diff --git a/drivers/power/ds2760_battery.c b/drivers/power/ds2760_battery.c
> index b82bf92..7b3043f 100644
> --- a/drivers/power/ds2760_battery.c
> +++ b/drivers/power/ds2760_battery.c
> @@ -78,7 +78,7 @@ MODULE_PARM_DESC(current_accum, "current accumulator value");
>  
>  /* Some batteries have their rated capacity stored a N * 10 mAh, while
>   * others use an index into this table. */
> -#define RATED_CAPACITY_FACTOR 10
> +#define RATED_CAPACITY_FACTOR 20

I'm a bit worried about this one.

Shouldn't this confuse batteries that already store rated
capacity with factor of ten? If so, please introduce a module
option.

Also, you don't update comments and module params description,
e.g.

  MODULE_PARM_DESC(rated_capacity, "rated battery capacity, 10*mAh or index");
  ....
  /* set rated capacity from module param (given in 10 * mAh) */

Is that intentionally?

Thanks!

-- 
Anton Vorontsov
email: cbouatmailru@...il.com
irc://irc.freenode.net/bd2
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