Re: /sys/class/power_supply/bq27200-0/capacity changed meaning between 4.1 and 4.4?

From: Andrew F. Davis
Date: Mon Jan 11 2016 - 09:47:58 EST

On 01/10/2016 02:06 AM, Pavel Machek wrote:

Did /sys/class/power_supply/bq27200-0/capacity change meaning between
4.1 and 4.4?

It used to report battery capacity remaining in percent.

Not sure what it reports now, but ain't in percent....

The patch does not compile, but I should be sleeping, not trying to
understand crazy code. Whoever wrote it, please fix it. Maybe you can
just do

...and more crazy code :-(.

cache.flags = bq27xxx_read(di, BQ27XXX_REG_FLAGS, has_singe_flag);
if ((cache.flags & 0xff) == 0xff)
cache.flags = -1; /* read error */
/* WTF? bq27xxx returns -ERRNO
on error, we mask some bits off it, and then make it -1... */

This is probably left over from when the driver was 1wire only, which seems
to fail by just reading back all ones. Not sure why the -1 though?

...and one crazy optimalization...

if (memcmp(&di->cache, &cache, sizeof(cache)) != 0)
di->cache = cache;

Hmmm, I think the lines above it:

if (di->cache.capacity != cache.capacity)

were at one point rolled into this as so:

if (memcmp(&di->cache, &cache, sizeof(cache)) != 0) {
di->cache = cache;

Otherwise that isn't an optimization, it probably takes more
time comparing than just doing the copy every time...

...are we playing obfuscated C code contest, yet?

val->intval = di->cache.flags < 0 ? 0 : 1; decidegree C?
if (ret == 0)
pval->intval -= 2731; /* convert decidegree k to c */

as read takes enum, make it enum like this?
static inline int bq27xxx_read(struct bq27xxx_device_info *di, enum bq27xxx_reg_index reg_index,
bool single)