On Thu, Apr 8, 2021 at 10:05 PM Konrad Dybcio <konradybcio@xxxxxxxxx> wrote: > On Qualcomm boards GPIOs that are used for "secure" (duh) peripherals, > like a fingerprint scanner, are not allowed to be controlled from Linux (the "non-secure world"). > Trying to do so causes an immediate reboot due to "attempting to violate the security". OK I see. Yeah HW security is pretty neat, making it cause a reboot seems like maybe not the best choice, but hey we know for sure what is wrong when it happens so it gives a good feeling of having everything fully inder control. Which is nice, despite the annoyance. > The GPIOs seem to all be iterated over on boot, except for the ones specified in > "gpio-reserved-ranges". (...) > So, why did it work before!? We do things like read all direction registers to check if GPIO lines are set up as input or output. If that causes reset then, well. > As a result, if such "secure" GPIOs are not declared in the DT, the board essentially dies on TLMM (pinctrl) probe > (which happens veeeery early - so that all other peripherals can set the pins as they see fit) > and that's very unpleasant to debug. Without this patch, Petr's device will simply not boot. In a way specifying it is a very correct thing to do. When they were registered with the GPIO subsystem before they were, well registered with the GPIO subsystem which means they are supposedly available for general-purpose input-output. Which they were not. They seem highly special-purpose to me. So reserving them is the right thing to do. Yours, Linus Walleij
