linaro-uboot: device tree without ramdisk and boot_relocate_fdt cause illegal memory access in kernel

[Shawn Guo]

On Fri, May 27, 2011 at 04:52:38PM +0800, Barry Song wrote:
> Hi all,
> i am using linaro uboot(u-boot-linaro-stable.git).  i have let our
> prima2 board support device tree with some workaround in uboot.  two
> problems i have meet:
> 1. device tree without ramdisk
> now uboot used commands like
> "bootm kernel_address  ramdisk_address dtb_address"
> to start linux kernel.
> in many cases, people have no ramdisk at all, but the following codes
> will still stop people to use device tree to start kernel since it got
> an illegal ramdisk:
> 
> common/cmd_bootm.c:
>         if (((images.os.type == IH_TYPE_KERNEL) ||
>              (images.os.type == IH_TYPE_MULTI)) &&
>             (images.os.os == IH_OS_LINUX)) {
>                 /* find ramdisk */
>                 ret = boot_get_ramdisk (argc, argv, &images, IH_INITRD_ARCH,
>                                 &images.rd_start, &images.rd_end);
>                 if (ret) {
>                         puts ("Ramdisk image is corrupt or invalid\n");
>                        return 1;
>                 }
> 
> #if defined(CONFIG_OF_LIBFDT)
>                 /* find flattened device tree */
>                 ret = boot_get_fdt (flag, argc, argv, &images,
>                                     &images.ft_addr, &images.ft_len);
>                 if (ret) {
>                         puts ("Could not find a valid device tree\n");
>                         return 1;
>                 }
> then i delete the first return 1 to let uboot ignore the ramdisk checking.
> 
> 2. boot_relocate_fdt in common/image.c
> this function will relocate fdt to an new address by:
> lmb_alloc_base(lmb, of_len, 0x1000, getenv_bootm_mapsize() + getenv_bootm_low())
> 
> but the return address is probably not in the initilized scale which
> kernel will build mapping in head.S. then in the function
> setup_machine_fdt() of arch/arm/kernel/devtree.c, when executing:
>          devtree = phys_to_virt(dt_phys);
> 
>         /* check device tree validity */
>         if (be32_to_cpu(devtree->magic) != OF_DT_HEADER)
>                 return NULL;
> kernel will die due to illegal memory access since dt_phys was not
> mapped to virtual address yet.
> 
> For problem1 , could uboot have a way to ignore ramdisk by itself?
> since we need 3 param in bootm to support device tree. For problem2,

bootm kernel_address - dtb_address

Use '-' for ramdisk address, if you do not have a ramdisk image.

> could uboot just relocate fdt to the original address of old ATAG,
> OFF+ 0x100?
> 
Do you have the following commit on your kernel tree?

commit 4d901c4271951d110afb13ee9aa73d27a6c8e53d
Author: Rob Herring <rob.herring at calxeda.com>
Date:   Wed Feb 2 16:33:17 2011 +0100

    ARM: 6648/1: map ATAGs when not in first 1MB of RAM

    If ATAGs or DTB pointer is not within first 1MB of RAM, then the boot params
    will not be mapped early enough, so map the 1MB region that r2 points to. Only
    map the first 1MB when r2 is 0.

    Some assembly improvements from Nicolas Pitre.

    Acked-by: Tony Lindgren <tony at atomide.com>
    Acked-by: Nicolas Pitre <nicolas.pitre at linaro.org>
    Signed-off-by: Rob Herring <rob.herring at calxeda.com>
    Signed-off-by: Russell King <rmk+kernel at arm.linux.org.uk>

You can get it from linux-linaro-2.6.38 tree.

-- 
Regards,
Shawn