On 13 January 2016 at 19:18, Nishanth Menon [off-list ref] 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 [off-list ref] 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