On 01/13/2016 12:44 PM, H. Nikolaus Schaller wrote: > > Am 13.01.2016 um 19:31 schrieb Nishanth Menon <nm@xxxxxx>: > >> On 01/13/2016 12:08 PM, H. Nikolaus Schaller wrote: >> [...] >> >>>> OK. So are we sure the TWL driver will never have to toggle this pin? >>> >>> After studying the Palmas TRM it appears that this pin just should be "high" >>> to be able to write to RTC and some scratchpad register. If the Palmas OTP >>> is programmed to use gpio7 as msecure input. >> >> Thanks for digging it up. we dont use the scratchpad, but in some cases >> where SoC cold reset is involved, those registers may store additional >> information. > > I remember a similar thing from omap3-twl4030 where the boot source is stored > so that a warm reboot searches there. But I don#t know if the OMPAP5 Boot ROM > is using that. > I believe that nonsense of OMAP ROM accessing PMIC stopped with OMAP3. I dont believe OMAP4 or any later generation processors does any PMIC access anymore - they instead make assumptions about specific voltage levels they will work on (So called OPP_BOOT) instead of assuming specific PMIC they will work with.. >>> Since the scratchpad is not used we can permanently enable msecure. Which >>> means that we must somehow get the driving output to be "1". >>> >>> This can be either done by >>> * a gpio with pull-up - switched to input mode as I proposed, or >> >> I think you intended to suggest to do a mux to gpio with just pinmux >> pull? > > Yes. > >> The internal pull on padconf is very weak >> - for typical needs like >> these, it is rather suggested to stick with real GPIO drive to prevent >> conditions like noise interference(for example). > > > well, on OMAP5 pull up/down are astonishingly strong :) > 100-250µA. Which translated roughly to 7 .. 18 kOhm @ 1.8V logic. > So a noise source must be coupled by an impedance in the 1 kOhm range. > This is quite rare. So I would not worry about that. > Interesting. I did not know that, and have'nt dug at people to confirm that either :). An internal feedback I got some time back on AM57 (not OMAP5) - context was that we were discussing if an external pull up resistor was needed for a GPIO button: "Internal pull-ups are relatively weak (ranging to 100kOhm or higher) and are good for avoiding higher leakage due to floating input level, and may not be sufficient for valid logic 1/0 depending on what else is connected on the board. If a signal must absolutely be pulled to a valid logic 1 or 0 for system functionality, then an external pull should be used." Anyways... will let Tony decide where he wants to go on this.. -- Regards, Nishanth Menon -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
