[PATCH/RFC v7] ARM: boot: Obtain start of physical memory from DTB

[Arnd Bergmann]

On Mon, Jul 20, 2020 at 11:45 AM Linus Walleij <linus.walleij at linaro.org> wrote:
>
> On Mon, Jul 6, 2020 at 5:03 PM Geert Uytterhoeven
>
> I tried to test this on the APQ8060 Qualcomm board. This is an odd beast,
> because physical memory starts at 0x40200000 which is 8MiB aligned,
> not even 16 MiB. Oddly this *works* with the mainline kernel, giving
> the following boot crawl:
>
> [    0.000000] cma: Reserved 256 MiB at 0x50000000
> [    0.000000] Zone ranges:
> [    0.000000]   Normal   [mem 0x0000000040200000-0x000000005fffffff]
> [    0.000000]   HighMem  empty
> [    0.000000] Movable zone start for each node
> [    0.000000] Early memory node ranges
> [    0.000000]   node   0: [mem 0x0000000040200000-0x0000000042dfffff]
> [    0.000000]   node   0: [mem 0x0000000048000000-0x000000005fffffff]
> [    0.000000] Initmem setup node 0 [mem 0x0000000040200000-0x000000005fffffff]
>
> It crashes so hard with this patch that I don't even get earlydebug
> messages. (Scary!)
>
> I also tried to simply load the kernel to 0x50000000 which solved
> an issue I had with KASan in the past, but it doesn't help. The
> first memblock is at 0x40200000 after all.
>
> Any hints at what may be going wrong here?
>
> No panic though - I know this platform is a stress test, but it'd be
> nice not to regress it.

No idea what /exactly/ is going wrong, but I would point out that this is one
of the platforms that is handled as a special case in the Makefile when
setting TEXT_OFFSET:

# Text offset. This list is sorted numerically by address in order to
# provide a means to avoid/resolve conflicts in multi-arch kernels.
textofs-y       := 0x00008000
# We don't want the htc bootloader to corrupt kernel during resume
textofs-$(CONFIG_PM_H1940)      := 0x00108000
# RTD1195 has Boot ROM at start of address space
textofs-$(CONFIG_ARCH_REALTEK)  := 0x00108000
# SA1111 DMA bug: we don't want the kernel to live in precious DMA-able memory
ifeq ($(CONFIG_ARCH_SA1100),y)
textofs-$(CONFIG_SA1111) := 0x00208000
endif
textofs-$(CONFIG_ARCH_IPQ40XX) := 0x00208000
textofs-$(CONFIG_ARCH_MSM8X60) := 0x00208000
textofs-$(CONFIG_ARCH_MSM8960) := 0x00208000
textofs-$(CONFIG_ARCH_MESON) := 0x00208000
textofs-$(CONFIG_ARCH_AXXIA) := 0x00308000
TEXT_OFFSET := $(textofs-y)

        Arnd