Hi Uwe, Thanks for your comment.
On Fri, Apr 16, 2021 at 11:44:26AM +0200, Uwe Kleine-König wrote: > Hello Nobuhiro, > > On Fri, Apr 16, 2021 at 05:07:21PM +0900, Nobuhiro Iwamatsu wrote: > > On Mon, Apr 12, 2021 at 09:02:32AM +0200, Uwe Kleine-König wrote: > > > On Mon, Apr 12, 2021 at 11:55:36AM +0900, Nobuhiro Iwamatsu wrote: > > > > On Sat, Apr 10, 2021 at 03:53:21PM +0200, Uwe Kleine-König wrote: > > > > > Can you please put a paragraph analogous to the one in pwm-sifive in > > > > > the > > > > > same format. This simplified keeping an overview about the oddities of > > > > > the various supported chips. > > > > > > > > OK, I will check pwm-sifive's, and add. > > > > I will add the following : > > > > * Limitations: > > * - PIPGM_PWMC is a 2-bit divider (00: 1, 01: 2, 10: 4, 11: 8) for the > > input > > * clock running at 1 MHz. > > I would strip that to: > > - Fixed input clock running at 1 MHz > OK, I will update. > > * - When the settings of the PWM are modified, the new values are shadowed > > * in hardware until the PIPGM_PCSR register is written and the currently > > * running period is completed. This way the hardware switches atomically > > * from the old setting to the new. > > * - Disabling the hardware completes the currently running period and keeps > > * the output at low level at all times. > > This looks fine. > > > > For me the critical (and only) difference between "off" and > > > "duty cycle = 0" is that when a new configuration is to be applied. In > > > the "off" state a new period can (and should) start immediately, while > > > with "duty_cycle = 0" the rising edge should be delayed until the > > > currently running period is over.[1] > > > > > > So the thing to do here (IMHO) is: > > > > > > Iff with PIPGM_PCSR = 0 configuring a new setting (that is finalized > > > with writing a non-zero value to PIPGM_PCSR) completes the currently > > > running period, then always assume the PWM as enabled. > > > > Yes, this device works that way. > > OK, then please use > > state->enabled = true > > unconditionally in visconti_pwm_get_state(). > Please let me check. If I unconditionally add 'state->enabled = true' to visconti_pwm_get_state(), state->enabled is set to true because visconti_pwm_get_state() is called when the device is created (this is when I write the device number to the export of /sys/class/pwm/pwmchip0 ). And since PIPGM_PCSR is 0 in this state, the pulse by PWM is not output. However, I think this means that the device is working as this driver. Is this correct? > Best regards > Uwe > Best regards, Nobuhiro
