Hi, I am working with the PowerPC 405 in the Virtex-II Pro FPGA. I've come across a possible problem where the device tree is located in at an address that the kernel cannot access if link_address (the location where zImage executes from, set in the "wrapper" script) is set too high (somewhere in the ballpark of 16 MB). Here is a summary of the problem:
In arch/powerpc/boot/main.c, ft_addr (a pointer to the flat? device tree) is computed and then passed on to "kentry" to the kernel startup code. At startup, the kernel only has access via the TLB to the first 16 MB of memory which is initialized by "initial_imu" in arch/powerpc/kernel/head_40x.S. The problem is that ft_addr is located relative to link_address / zImage, but this address might be outside of the bounds of the 16MB initially mapped by the TLB. A symptom of this problem is that the kernel ceases to print any messages to the console because it could not read information about the console from the flat device tree. The last thing the user will see is this: zImage starting: loaded at 0x04000000 (sp: 0x0430beb0) Allocating 0x6f11b0 bytes for kernel ... gunzipping (0x00000000 <- 0x0400c000:0x0430a31a)...done 0x657000 bytes Linux/PowerPC load: console=ttyUL0 root=/dev/ram Finalizing device tree... flat tree at 0x4318300 ...and then the screen goes completely blank... And it seems that the kernel also eventually crashes (but I couldn't tell exactly what happened because __log_buf repeatedly gets corrupted with zeros whenever I try this particular experiment). Maybe there is also more to this problem too than just the ft_addr. -David _______________________________________________ Linuxppc-dev mailing list Linuxppc-dev@lists.ozlabs.org https://lists.ozlabs.org/listinfo/linuxppc-dev
