On 13 January 2016 at 19:18, Nishanth Menon <nm@xxxxxx> wrote: > As you already see it is ridiculously round about way of protecting RTC > time.. but anyways, for what ever reason, that was mandatory function to > support on certain product lines. Having secure date/time is probably necessary for some digital rights management schemes; e.g. you rent a movie for limited time, but it may not always be acceptable to require working internet connectivity to be able to hit the play button hence the need to rely on a secure RTC. There wouldn't even be an SMC for setting the RTC, probably it would synchronize when the secure-world shizzle contacts the Big Server O'Secrety Bits. :P Protecting pinmux through the L4 firewall sounds hilarious: the whole ctrl_core module (0x4a002000 - 0x4a002fff) is a single firewall region. All permitted access to it by linux would have to be redirected to an SMC or similar. On 13 January 2016 at 20:05, Nishanth Menon <nm@xxxxxx> wrote: > 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) Unlike the OMAP5, AM57xx uses 1.8V/3.3V drivers for its generic IOs, which have to do magic to not get fried by such high voltages. Crappier specs result, especially for pulling up to 3.3V: 1.8V mode, pull-down current while pin is held high: 50-210 uA 3.3V mode, pull-down current while pin is held high: 40-200 uA 1.8V mode, pull-up current while pin is held low: 60-200 uA 3.3V mode, pull-up current while pin is held low: 10-290 uA Note the worst-case equivalent pull-up resistance in 3.3V mode is 330 kOhm, eleven times higher than in 1.8V mode. Matthijs -- 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
