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

[Simon Guinot]

On Tue, Jun 04, 2013 at 08:52:12AM +0200, Arnaud Ebalard wrote:
> 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

OK you are lucky. Your bootloader initialize set_cnt with 0x5a. Mine
don't and it is precisely the issue: set_cnt is still 0xff (the default
value) when the driver controls the fan.

Please, could you try open-loop mode with set_cnt set to 0xff ?  Maybe
you can enforce this value for the test purpose ?

If you observe the same behaviour than me, then could modify the driver
to ensure that set_cnt is not 0xff when open-loop mode is selected ?
Maybe by systematically setting a different value (as 0) ?

> 
> 
> > 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.

Actually, I have only problems when set_cnt worths 0xff. Please, could
you try the tests mentioned above ?

Thanks in advance,

Simon

> 
> Cheers,
> 
> a+
> 
> _______________________________________________
> linux-arm-kernel mailing list
> linux-arm-kernel at lists.infradead.org
> http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
-------------- next part --------------
A non-text attachment was scrubbed...
Name: signature.asc
Type: application/pgp-signature
Size: 198 bytes
Desc: Digital signature
URL: <http://lists.infradead.org/pipermail/linux-arm-kernel/attachments/20130604/314cbb54/attachment.sig>