Hi Uwe, > From: Uwe Kleine-König, Sent: Friday, December 7, 2018 7:46 PM > > Hello, > > On Fri, Dec 07, 2018 at 10:57:48AM +0100, Geert Uytterhoeven wrote: > > > Is the documentation for this hardware publically available? > > > > Please check Section 59 of the "User's Manual: Hardware" at > > https://www.renesas.com/eu/en/products/microcontrollers-microprocessors/rz/rzg/rzg1m.html > > Thanks. > > So the ugly things here are: > > a) if the pwm is stopped (PWMCR.ENO = 0) the output is set to high after > completion of the currently running period. > b) setting a duty_cycle of 0 is forbidden Thank you for checking the hardware specification. > both are bad. A workaround for both is implementation of something > similar to the switch to a gpio suggested by Michal for imx. But this > cannot be done reliably because the current period's end isn't > observable. I agree. This R-Car PWM needs special handling when the driver disable the PWM. > Alternatively a confirmation from the Renesas engineers that PWMCNT.PHO > can be set to 0 with the intended effect despite being forbidden in the > reference manual would be great. Did someone with access to such > hardware test what happens if the PHO field is set to 0? Maybe the > forbidden value is just a wrong copy&paste from the CYCO field? I'm asking HW guy about this specification now. # According to the state machine in the manual, it seems the PWM cannot output # low level when the PWM is enabled though... > I think it would be a good idea to add the link to the documentation > into a comment at the top of the driver. I think so. Best regards, Yoshihiro Shimoda > @Thierry: Given that nobody seems to have an overview about the features > and ugly implementation details of all the PWMs, what about documenting > them in the driver files in a greppable way. For the rcar driver > something like: > > - duty-counter-bits: 10 > - period-counter-bits: 10 > - hardware-polarity-support: false > - uglyness: > - OUTPUT-ACTIVE-ON-DISABLE > - NO-ZERO-DUTY-CYCLE > > Best regards > Uwe > > -- > Pengutronix e.K. | Uwe Kleine-König | > Industrial Linux Solutions | http://www.pengutronix.de/ |
