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SubjectRe: [PATCH 07/14 v3] bq27x00: Cache battery registers
On 02/14/2011 10:58 PM, Grazvydas Ignotas wrote:
> On Mon, Feb 14, 2011 at 5:01 AM, Lars-Peter Clausen <lars@metafoo.de> wrote:
>> This patch adds a register cache to the bq27x00 battery driver.
>> Usually multiple, if not all, power_supply properties are queried at once,
>> for example when an uevent is generated. Since some registers are used by
>> multiple properties caching the registers should reduce the number of
>> reads.
>>
>> The cache is valid for 5 seconds this roughly matches the internal update
>> interval of the current register for the bq27000/bq27200.
>>
>> Fast changing properties(*_NOW) which can be obtained by reading a single
>> register are not cached.
>>
>> It will also be used in the follow up patch to check if the battery status
>> has been changed since the last update to emit power_supply_changed events.
>>
>> Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
>> ---
>> drivers/power/bq27x00_battery.c | 271 +++++++++++++++++++++-----------------
>> 1 files changed, 150 insertions(+), 121 deletions(-)
>>
>> diff --git a/drivers/power/bq27x00_battery.c b/drivers/power/bq27x00_battery.c
>> index 44bc76b..dbe3fcb 100644
>> --- a/drivers/power/bq27x00_battery.c
>> +++ b/drivers/power/bq27x00_battery.c
>
> <snip>
>
>> -static int bq27x00_battery_current(struct bq27x00_device_info *di)
>> +static int bq27x00_battery_current(struct bq27x00_device_info *di,
>> + union power_supply_propval *val)
>> {
>> - int ret;
>> - int curr = 0;
>> - int flags = 0;
>> + int curr;
>>
>> - ret = bq27x00_read(di, BQ27x00_REG_AI, &curr, false);
>> - if (ret) {
>> - dev_err(di->dev, "error reading current\n");
>> - return 0;
>> - }
>> + if (di->chip == BQ27500)
>> + curr = bq27x00_read(di, BQ27x00_REG_AI, false);
>> + else
>> + curr = di->cache.current_now;
>> +
>> + if (curr < 0)
>> + return curr;
>
> This is wrong, as read function returns negative values for bq27500
> when discharging. That's why read function used to pass value through
> argument before your series (return value was for error code).

I don't think so. The register is 16bit wide and it is read as a unsigned. So
in the non error case bq27x00_read will always return >= 0.
The value is later reinterpreted as a signed 16bit.(See the other lines you
quoted underneath).

Did you experience any actual problem with current being wrong?

>
> Sorry for not noticing this earlier, I only found this now during testing.
>
>>
>> if (di->chip == BQ27500) {
>> /* bq27500 returns signed value */
>> - curr = (int)((s16)curr) * 1000;
>> + val->intval = (int)((s16)curr) * 1000;

- Lars


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