[PATCHv2 1/3] Add support for GMT G762/G763 PWM fan controller

[Arnaud Ebalard]

Hi Simon,

Simon Guinot <simon.guinot at sequanux.org> writes:

> On Sat, Jun 01, 2013 at 07:26:54PM +0200, Arnaud Ebalard wrote:
>> Hi Simon and Guenter,
>> 
>> Simon Guinot <simon.guinot at sequanux.org> writes:
>> 
>> > On Tue, May 28, 2013 at 12:03:14AM +0200, Arnaud Ebalard wrote:
>> >> 
>> >> Signed-off-by: Arnaud Ebalard <arno at natisbad.org>
>> >> ---
>> >>  drivers/hwmon/Kconfig              |   10 +
>> >>  drivers/hwmon/Makefile             |    1 +
>> >>  drivers/hwmon/g762.c               | 1012 ++++++++++++++++++++++++++++++++++++
>> >>  include/linux/platform_data/g762.h |   54 ++
>> >>  4 files changed, 1077 insertions(+)
>> >>  create mode 100644 drivers/hwmon/g762.c
>> >>  create mode 100644 include/linux/platform_data/g762.h
>> >
>> > Hi Arnaud,
>> >
>> > After more tests on my 2Big Network v2 board, it appears that the fan
>> > doesn't rotate when PWM mode (the preferred operating mode for this
>> > board) is selected. Nevertheless, DC mode is usable (even if not ideal
>> > given the hardware). After some investigations I noticed that an extra
>> > initialization is needed to enable PWM mode on my board: the set_cnt
>> > register must be set to 0 while the default value is 0xff. Is that
>> > specific to my hardware ? Is PWM mode working on your ReadyNAS with
>> > the default set_cnt value ?
>> 
>> First, thanks for testing this!
>> 
>> Regarding your problem, I first started by booting current version of my
>> driver on the Duo v2 w/o touching chip registers (only clock reference
>> value). This way, I inherit the values installed by (NETGEAR's) u-boot:
>> 
>> $ for k in fan* pwm* ; do echo -n "$k:" ; echo `cat $k `; done
>> fan1_alarm:0
>> fan1_div:2
>> fan1_fault:0
>> fan1_input:1807
>> fan1_target:1807
>> pwm1:221
>> pwm1_enable:2        /* closed-loop, i.e. config is done via set_cnt */
>> pwm1_mode:1          /* PWM mode */ 
>
> Sorry, I realize that I have not been very accurate in my description of
> the problem: The fan doesn't rotate when PWM _and_ open-loop control are
> selected. On the 2Big2 board, 2 wires are used to drive the fan.
>
> Then with pwm1_mode=1, pwm1_enable=1 and set_cnt=0xff (default value),
> nothing happen whatever the value I write in pwm1.

After boot, with set_cnt and set_out untouched by me (set_cnt set to
0x5a by u-boot, i.e. 255-0x5a read on pwm1):

fan1_alarm:0
fan1_div:1
fan1_fault:0
fan1_input:1365
fan1_target:1365
pwm1:0                  /* set_out is 0 (considering fan1_target,
                           set_cnt is 0x5a)*/
pwm1_enable:2           /* closed-loop */
pwm1_mode:0             /* DC mode */

# echo 1 > pwm1_mode    /* PWM mode */       # fan rotates 
# echo 1 > pwm1_enable  /* open-loop */      # fan stops rotating

At that point we have:

fan1_alarm:0
fan1_div:1
fan1_fault:0
fan1_input:0
fan1_target:1365
pwm1:0                  /* set_out is 0, set_cnt is still 0x5a */
pwm1_enable:1
pwm1_mode:1

Then:

# echo 100 > pwm1                            # fan rotates


> By testing, I have discovered that writing 0 into set_cnt allows to work
> around the issue. I can do this by using the closed-loop control:
> pwm1_mode=1, pwm1_enable=2 and pwm=255. Now, set_cnt worths 0 and if I
> switch back to open-loop control, all works as expected.
>
> Can you try open-loop control and PWM mode with your board ? I wonder if
> this issue is specific to the 2Big2 hardware.

AFAICT, set_cnt has never been set to 0 in my test and PWM+open-loop
works as expected, i.e. just by setting a non-zero value in set_out.
Tell me if I missed something or if you want me to perform another
test.

Cheers,

a+