why doesn't arm virt machine boot linux when uart address size is increased?

[ckim]

Hello all,

 

Earlier, I have copied the arm/virt machine and named it ab21q.

I changed the memory map of ab21q to match our system (under development).

Among others the original UART address/size was changed from {0x09000000, 0x1000} to {0x10210000, 0xf000}. (the numbers were given to me)

I checked a couple of baremetal programs run ok on the new machine.

But when I tried running linux on ab21q this morning, the linux kernel didn’t to the shell prompt.

(Seen using debugger, it runs to the end of start_kernel function, but nothing happens after that point, whereas the original ‘virt’ machine gives me booting messages from that point)

But if I change the UART address/size to {0x10210000, 0x1000}, it boots ok.

I know the UART doesn’t need that amount (0xf000) of space, but why doesn’t linux boot with this UART address range size?

I checked even for ‘virt’ machine, if I increase the UART address size to 0x2000 from 0x1000, it doesn’t boot.

I am curious about what mechanism is preventing it from booting when the UART address space size is bigger than necessary and also what the kernel is doing during the 3~4 seconds after the end of start_kernel function and printing “Booting from ..” message.

(I am aware the ‘virt’ machine makes the flattend device tree and passes it to the OS for booting)

Thanks!

 

Chan Kim