问题
I'm currently working on a i.mx257 platform and want to read some peripheral registers (the iomux register to be specific) to see how it is configured or if it is set right.
I've read about the devmem from busybox and devmem2, too. Tried both and both get an error. Currently there the custom board is running linux kernel version 4.6.0-rc7 from the meta-fsl-arm yocto meta package. The system is built with yocto.
root@system /]#./tmp/devmem2 0x43fac190 /dev/mem opened.
Unhandled fault: external abort on non-linefetch (0x008) at 0xb6f3a190 pgd = c3334000 [b6f3a190] *pgd=8285e831, *pte=43fac103, *ppte=43facaa2
Memory mapped at address 0xb6f3a000.
Bus error
The tool gets an Signal Err. The CONFIG_STRICT_DEVMEM option is not set in the kernel config.
I found another post http://thread.gmane.org/gmane.linux.ports.arm.kernel/26878 but I can't find some information about these registers for an i-mx25.
Is there another kernel security feature or something I'm missing?
The devmem or devmem2 is only working with values below 0x4000. For all addresses above i get the signal bus error.
回答1:
Okay, i found an answer to my own question. The AIPS control registers have to be added to the devicetree. They are protecting the register i want to read. After i added these patches it worked.
https://github.com/torvalds/linux/commit/24bb244e02a6bead5b854d842002df0d38ae7b7b
https://github.com/torvalds/linux/commit/c33576cbf86bedf9ad3812479c3b4f36d5fadba8#diff-64c444a874c565fd98cf1ab538c1e0cd
来源：https://stackoverflow.com/questions/47569718/linux-register-read-arm-i-mx257-from-userland-devmem-not-working