linux-kernel - Re: [PATCH 8/9] bq27x00: Add miscdevice for each battery with ioctl for reading registers

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Date:	Tue, 01 Nov 2011 13:09:40 +0100
From:	Lars-Peter Clausen <lars@...afoo.de>
To:	Pali Rohár <pali.rohar@...il.com>
CC:	linux-kernel@...r.kernel.org, Anton Vorontsov <cbou@...l.ru>,
	syed rafiuddin <rafiuddin.sayed@...il.com>,
	Rodolfo Giometti <giometti@...ux.it>,
	David Woodhouse <dwmw2@...radead.org>
Subject: Re: [PATCH 8/9] bq27x00: Add miscdevice for each battery with ioctl
 for reading registers

On 11/01/2011 01:43 AM, Pali Rohár wrote:
> * When bq27x00_battery module is loaded it take control of bq27200 i2c battery chip and then it is not possible to use i2cget program from user space (returns -EBUSY)
> * This patch adds new miscdevice for each battery which has ioctl BQ27X00_READ_REG for reading battery registers from user space
> 
> * ioctl cmd:
>   #define BQ27X00_READ_REG _IO(MISC_MAJOR, 0)
> 
> * ioctl arg:
>   struct bq27x00_reg_parms {
>     int reg; /* battery register (in) */
>     int single; /* 1 - 8bit register, 0 - 16bit register (in) */
>     int ret; /* register status, negative indicate error (out) */
>   };
> 
> Signed-off-by: Pali Rohár <pali.rohar@...il.com>

I'm not sure if this is such a good idea. Why do you need to read the registers
from userspace? Shouldn't all relevant information be available in a
standardized format through the power_supply userspace API? If you want to use
it for debugging it might be a better idea to provide a debugfs file.

- Lars
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