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SubjectRe: [PATCH 0/5] hwmon: New hwmon registration API
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Hi Punit,

On 07/08/2016 02:31 AM, Punit Agrawal wrote:
> Hi Guenter,
>
> Guenter Roeck <linux@roeck-us.net> writes:
>
>> Up to now, each hwmon driver has to implement its own sysfs attributes.
>> This requires a lot of template code, and distracts from the driver's
>> core function to read and write chip registers.
>>
>> To be able to reduce driver complexity, move sensor attribute handling
>> and thermal zone registration into the hwmon core. By using the new API,
>> driver size is typically reduced by 20-50% depending on driver complexity
>> and the number of sysfs attributes supported.
>>
>> The first patch of the series introduces the API as well as support
>> for temperature sensors. Subsequent patches introduce support for
>> voltage, current, power, energy, humidity, and fan speed sensors.
>>
>> The series was tested by converting several drivers (lm75, lm90, tmp102,
>> tmp421, ltc4245) to the new API. Testing was done with with real chips
>> as well as with the hwmon driver module test code available at
>> https://github.com/groeck/module-tests.
>
> I like this series - it takes all of the attributes' handling out of the
> individual driver code and moving it to hwmon core.
>
> Having attempted a port of scpi-hwmon.c, I think that driver will not
> gain a big savings in line count. Though it'll help separate access to
> sensors from sysfs related code - which I think is worth the change.
>

From what I have seen, savings are for the most part on the binary image size.
I have not seen much if any savings in terms of LOC, though that may in part
be because of my coding style.

Here is the result from the conversions I have done so far.

Old:

text data bss dec hex filename
5730 4056 64 9850 267a drivers/hwmon/lm95245.o
5941 4240 64 10245 2805 drivers/hwmon/lm95241.o
5361 3584 64 9009 2331 drivers/hwmon/jc42.o
8609 10872 64 19545 4c59 drivers/hwmon/max31790.o
9080 13232 64 22376 5768 drivers/hwmon/nct7904.o
6574 8498 64 15136 3b20 drivers/hwmon/ltc4245.o
4516 3464 64 8044 1f6c drivers/hwmon/tmp421.o
4223 2744 64 7031 1b77 drivers/hwmon/tmp102.o
21757 13496 64 35317 89f5 drivers/hwmon/lm90.o
6804 3240 64 10108 277c drivers/hwmon/lm75.o

New:

text data bss dec hex filename
5166 1568 128 6862 1ace drivers/hwmon/lm95245.o
4334 1664 64 6062 17ae drivers/hwmon/lm95241.o
4579 1456 64 6099 17d3 drivers/hwmon/jc42.o
3687 1312 64 5063 13c7 drivers/hwmon/max31790.o
3905 1720 64 5689 1639 drivers/hwmon/nct7904.o
3989 1658 64 5711 164f drivers/hwmon/ltc4245.o
3557 1408 64 5029 13a5 drivers/hwmon/tmp421.o
4037 2200 64 6301 189d drivers/hwmon/tmp102.o
16485 4288 64 20837 5165 drivers/hwmon/lm90.o
5762 2128 64 7954 1f12 drivers/hwmon/lm75.o

This is with x86_64.

The largest savings are in drivers with simple access methods and
a large number of attributes. The scpi driver is somewhat of an
exception since it creates its attribute data structures dynamically;
I would not expect to see much savings in that driver.

> FWIW,
>
> Acked-by: Punit Agrawal <punit.agrawal@arm.com>
>

Thanks!

Guenter

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