On Thu, Mar 21, 2019 at 09:35:26PM +0800, zhuchangc...@cvte.com wrote: > --> I know your meaning, even though I've did following actions > instead of unexport, > > # echo 0 > /sys/class/gpio/gpioXX/value > # echo in > /sys/class/gpio/gpioXX/direction > > the padcfg0 value still can not roll back,because after export the > gpio,the following > > action as padcfg0 settings was done. > > Exactly TX and RX register have been set as below in GPIO request: > > /* Disable TX buffer and enable RX (this will be input) */ > > value &= ~PADCFG0_GPIORXDIS; > > value |= PADCFG0_GPIOTXDIS; > > this will infruence next reboot gpio signal. > > And could you pls see my ->free function implementation?
I checked it and you do this: + value |= PADCFG0_GPIORXDIS; + value &= ~PADCFG0_GPIOTXDIS; which pretty much turns the pin GPIO output unconditionally. I don't really think it is good idea. May work in your case but may cause problems with others. If you want to keep it as output and leave the value 1 (high) before you issue reboot, I don't think you need to do anything via sysfs (as the pin is already in that state and issuing reboot command should not change anything because the driver does not have ->shutdown callback. In other words, your peripheral expects reset GPIO to be asserted (high) during reboot so unless the boot firmware resets the pin I don't see why leaving it as is does not work for you.