On Thu, Nov 21, 2013 at 12:23 PM, Grant Likely <grant.likely@xxxxxxxxxxxx> wrote: > On Thu, Nov 21, 2013 at 12:21 PM, Grant Likely > <grant.likely@xxxxxxxxxxxx> wrote: >> On Tue, 19 Nov 2013 12:12:26 +0100, Geert Uytterhoeven <geert@xxxxxxxxxxxxxx> 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@xxxxxxxxxxx> >>> Signed-off-by: Geert Uytterhoeven <geert@xxxxxxxxxxxxxx> >>> --- >>> 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. Okay, I've got one more comment on this. I know that some architectures use unflatten_and_copy_devicetree() to sort out the dtb copy problem. My point here is that for this to become generic code then early_init_dt_scan() needs to grow the ability to differentiate between a DT that needs to be copied (built in) vs. a DT that is already in safe memory. The contents of unflatten_and_copy_devicetree() could even be rolled into unflatten_devicetree() if there is a common way to indicate whether or not the DT needs to be copied that early_init_dt_scan() can manipulate. ie. a global flag. g. -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html