[RFC] [PATCH V2] Adding DTB to architecture independent vmlinux

[David VomLehn]

On Thu, Oct 28, 2010 at 08:18:25AM -0700, H. Peter Anvin wrote:
> On 10/27/2010 5:57 PM, David VomLehn wrote:
>>
>> I've been playing a bit with the patch, and would suggest something
>> like the following for the second target:
>>
>> 	$(obj)/%.dtb.S: $(obj)/%.dtb
>> 		@echo '#include<asm/page.h>'>$@
>> 		@echo '.balign PAGE_SIZE'>>  $@
>> 		@echo '.section .kernel:dtb,"a"'>>  $@
>> 		@echo '.global __$(*F)_dtb'>>  $@
>> 		@echo '__$(*F)_dtb:'>>  $@
>> 		@echo '.incbin "$<" '>>  $@
>> 		@echo '.balign PAGE_SIZE'>>  $@
>>
>> Advantages:
>> 1.	Each blob gets a name that can be used to refer to it. This
>> 	allows multiple blobs to be built into a kernel, each with
>> 	its own name.  The name of each blob is taken from the file
>> 	name, so a source
>> 	file abc.dts would produce a blob referred to as __abc_dtb.
>> 2.	Blobs are aligned on a page boundary and extend to the nearest
>> 	page boundary. Any blobs you don't care about can then easily
>> 	be completely freed.
>>
>> You might then use:
>>
>> 	obj-y += $(addprefix .dtb.o,$(PLATFORM_DTB))
>>
>> to add blob names, but I'm not completely confident this is the way to go.
>
> To be able to specify "dtb=<name>" on the command line, you want the  
> name to be manifest in string form, rather than as a symbol.  That means  
> putting a header or something similar in front of the blobs.

Could you not iterate over the blobs and use the "compatible" property to
match the string? It would seem to me that this would be the right thing
to do in any case since it would then follow the standard method for
interpreting that property.

> How big are these blobs in the typical case?  Padding to the page size  
> could easily add more waste than it saves.  In that case it probably  
> would be better to put the stuff in the init area and copy the active  
> blob to an allocated location.

In my case, where there are a lot of up-front reservations of memory
at a static address, there is a fair amount of work to do before
it's possible to do the dynamic address allocation for the blob's
ultimate destination, but I'm okay with either doing blob size and address
rounding or copying it from init. I don't see a benefit of supporting
multiple approaches for Linux.

> 	-hpa

-- 
David VL