Hi Franklin, 

On Thu, 18 Feb 2016, Franklin S Cooper Jr. wrote:

On 02/18/2016 12:58 AM, Paul Walmsley wrote:

quoted

OK I'm not sure I understand what's going on, particularly the part about 
locking and unlocking.  Are you saying that the pwm_bl driver calls into 
the pwm_tiecap module to write to the PWMSS_CLKCONFIG registers to ungate 
the ECAP clock, and then the hardware silently ignores the write?  If 
that's the case, shouldn't we be seeing some warning messages from a 
failure to ungate the clock from a subsequent PWMSS_CLKSTATUS poll?  Or am 
I misunderstanding what's going on here?

Pwm-tipwmss.c exports a function
pwmss_submodule_state_change which interacts with
PWMSS_CLKCONFIG and PWMSS_CLKSTATUS registers. Both
pwm-tiehrpwm.c and pwm-tiecap.c calls this exported function
to unlock the gate at probe time and lock the gate when the
driver is removed.

So when the gate fails to be unlocked after it previously is
locked there isn't a way to know this via the
PWMSS_CLKSTATUS registers.

OK I understand now.  Sounds like the gating -> ungating transition is 
effectively a one-time operation, and once the ungating -> gating 
transition is done, there's no way to reverse it.  Please correct me if 
I've got it wrong.

 So the driver "believes" that the gate is unlocked and when pwm_bl runs 
it calls the set_polarity function. Set_polarity in the case of AM437x 
gp evm maps to the ecap's ecap_pwm_set_polarity function call. This call 
then attempts to write to the ecap registers which results in the 
external abort since the clock to the ecap is still gated.

When the ecap and tihrpwm driver request to unlock the clock
gate it already checks the XXX_CLK_EN_ACK bitfields within
CLKSTATUS and it shows that the clocks "should" be unlocked.
So there is an issue with the IP.

OK

Yes, I plan on addressing the change Vignesh acknowledged
regarding changing RESETSTATUS to SOFTRESET. For your other
comments I believe he already explained why it has to be set
in that particular way. If there is anything that I missed
or something that isn't clear please let me know.

Perfect, thanks for the good description and the followup.


- Paul