Messages in this thread |  | | From | Grant Likely <> | Date | Thu, 21 Nov 2013 12:23:44 +0000 | Subject | Re: [PATCH 1/9] dt: Handle passed/built-in DT selection in early_init_dt_scan() |
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On Thu, Nov 21, 2013 at 12:21 PM, Grant Likely <grant.likely@secretlab.ca> wrote: > On Tue, 19 Nov 2013 12:12:26 +0100, Geert Uytterhoeven <geert@linux-m68k.org> wrote: >> Let early_init_dt_scan() fall-back to the built-in DT if no DT was passed, >> or if it's invalid, so architectures don't have to duplicate this logic. >> >> Suggested-by: Rob Herring <rob.herring@calxeda.com> >> Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org> >> --- >> drivers/of/fdt.c | 24 +++++++++++++++++------- >> include/linux/of_fdt.h | 1 + >> 2 files changed, 18 insertions(+), 7 deletions(-) >> >> diff --git a/drivers/of/fdt.c b/drivers/of/fdt.c >> index 2fa024b97c43..a797cd43bc8b 100644 >> --- a/drivers/of/fdt.c >> +++ b/drivers/of/fdt.c >> @@ -868,18 +868,28 @@ void * __init __weak early_init_dt_alloc_memory_arch(u64 size, u64 align) >> >> bool __init early_init_dt_scan(void *params) >> { >> - if (!params) >> - return false; >> - >> /* Setup flat device-tree pointer */ >> initial_boot_params = params; >> >> - /* check device tree validity */ >> - if (be32_to_cpu(initial_boot_params->magic) != OF_DT_HEADER) { >> - initial_boot_params = NULL; >> - return false; >> + /* check passed device tree validity */ >> + if (initial_boot_params && >> + be32_to_cpu(initial_boot_params->magic) == OF_DT_HEADER) { >> + pr_info("FDT at %p\n", initial_boot_params); >> + goto found; >> + } >> + >> + /* check built-in device tree validity */ >> + initial_boot_params = &__dtb_start; >> + if (__dtb_end != (void *)&__dtb_start && >> + be32_to_cpu(initial_boot_params->magic) == OF_DT_HEADER) { >> + pr_info("Compiled-in FDT at %p\n", initial_boot_params); >> + goto found; > > __dtb_start is in an init section which is discarded after initcalls. > For this to work, the dtb needs to be copied into a region of allocated > memory. The dtb section can also potentially contain multiple .dtb > blobs. In the use case that you care about you are probably only > thinking about one, but it is entirely possible for device drivers to > have a dtb linked in which may break this if it gets linked in a > different order. The specific example I'm thinking about is I want to > have the DT selftest code load an overlay to get testcase data from a > dtb blob. > > The other concern I have here is that I don't really want this to be the > default on a lot of platforms. ARM and PowerPC for instance should only > get the default dtb from the boot wrapper. It needs to be configurable > in some way. > > Instead of using __dtb_start, it would probably solve both of the above > problems if the build-in DTB has a specific label identifying it as the > default DT.
Er, not quite. It still doesn't solve the init section discard problem. That still needs solving.
g.
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