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

[Arnaud Ebalard]

Hi Simon,

arno at natisbad.org (Arnaud Ebalard) writes:

> 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 */ 
>
> If G762 datasheet is correct, NETGEAR's u-boot alters fan divisor ('01'
> i.e. 2 instead of '00' i.e. 1). It also changes the default mode from
> linear to pwm and sets set_cnt to 34 (255-221). 
>
> Then, I grabbed the GPL sources (5.3.7) of NETGEAR's u-boot and found
> the following in a boot function:
>
>  /* Turn G76x(FAN controller, i2c address 0x3e) on.
>   * The FAN_SET_CNT register's offset is 0x0.
>   * Set [1300(rpm) == 65% == 5a(FAN_SET_CNT)] as default.
>   */
>  unsigned char byte=0x5a;
>  if(i2c_write(0, 0x3e, 0x0, 1, &byte, 1) != 0) 
>    puts ("Error writing the i2c chip : G76x(Fan controller).\n");
>
> AFAICT, this is the only location in the whole source tarball where 0x3e
> reg is modified in an i2c function. 
>
>
> Then, I grabbed the u-boot source code from NETGEAR for ReadyNAS 102
> (Armada-370 based NAS, also using a G762) and it has the following:
>
>  /* Turn G76x(FAN controller, i2c address 0x3e) on.
>   * The FAN_SET_CNT register's offset is 0x0.
>   * Set [1300(rpm) == 65% == 5a(FAN_SET_CNT)] as default.
>   */
>  MV_U8 byte=0x5a;
>  if(i2c_write(0x3e, 0x0, 1, &byte, 1) != 0)
>  	puts ("Error writing the i2c chip : G76x(Fan controller).\n");
>  /* Tune the FAN_STARTV */
>  if (i2c_read(0x3e, 0x5, 1, &byte, 1) != 0)
>  	puts ("Error reading the i2c chip : G76x(Fan controller).\n");
>  byte |= 0x3;
>  if(i2c_write(0x3e, 0x5, 1, &byte, 1) != 0)
>  	puts ("Error writing the i2c chip : G76x(Fan controller).\n");
>  
> In the end, it does not seem NETGEAR's u-boot does some specific things
> except setting a non-zero value to SET_CNT register for the fan to start
> rotating.
>
> BTW, if you wonder why some attributes reported at the beginning have
> different values than the ones in the datasheet (0x5a set in u-boot,
> reading 0x22) although NETGEAR's u-boot code does not seem to tamper
> those, I don't have the answer. 

I was not happy with previous result and did some additional tests.
Between each tests, I did a full power off (halt and removal of power
cable) of the device instead of a simple reboot. With a power off, I
get the following:

fan1_alarm:0
fan1_div:1
fan1_fault:0
fan1_input:1365
fan1_target:1365
pwm1:0
pwm1_enable:2
pwm1_mode:0

Note that fan1_target reflects the fact that set_cnt is 165 (i.e. 255 -
0x5a), which is exactly what NETGEAR's u-boot sets for this reg.

Now, if I do a simple restart, there is some hysteresis which explains
the weird difference in my first test.

Another message follows w/ additional answers to your problem.

Cheers,

a+