[U-Boot] [PATCH 62/71] serial: spl: Implement empty functions for SPL

[Tom Rini]

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On 09/18/12 12:25, Marek Vasut wrote:
> Dear Tom Rini,
> 
>> On 09/18/12 12:19, Marek Vasut wrote:
>>> Dear Tom Rini,
>>> 
>>>> On 09/18/12 11:33, Marek Vasut wrote:
>>>>> Dear Scott Wood,
>>>> 
>>>> [snip]
>>>> 
>>>>>> I think I got some wires crossed and was thinking about 
>>>>>> printf/puts. We want those to be optimized away at
>>>>>> compile time (not pointed to a stub at link time) on an
>>>>>> SPL that has no output support, but once that's done the
>>>>>> low level serial functions shouldn't be referenced
>>>>>> anymore, right?
>>>>> 
>>>>> But if you point them to stubs, that's OK. The compiler
>>>>> will GC these useless stubs anyway. But wait, we're getting
>>>>> to LTO here, right?
>>>>> 
>>>>> So the safest bet really is macro in serial.h ?
>>>> 
>>>> Due to the gcc bug I've mentioned before, yes.  Dummy
>>>> functions will, I bet, keep the string constants around.  do
>>>> {} while(0) will drop them out entirely.
>>> 
>>> Damn, not much gain on m28evk (with C functionss/with macros), 
>>> using gcc 4.7.1:
>>> 
>>> Configuring for m28evk board... text    data     bss     dec
>>> hex filename 418994    7780  288632  715406   aea8e ./u-boot
>>> 11773 788 12   12573    311d ./spl/u-boot-spl
>>> 
>>> Configuring for m28evk board... text    data     bss     dec
>>> hex filename 418998    7780  288628  715406   aea8e ./u-boot
>>> 11765 788 12   12565    3115 ./spl/u-boot-spl
>> 
>> Right, didn't have many strings.  But do you see what I mean now
>> about not needing this patch as it stands currently?
> 
> No, I don't. If I remove this patch, the build breaks either
> because serial_* is defined twice or not defined at all.

m28evk currently, needlessly, defines serial_puts/putc.  I locally
patched master to drop them from arch/arm/cpu/arm926ejs/mxs/spl_boot.c
and the references in common/libcommon.o are correctly
garbage-collected.  They are in fact unused functions today as they're
garbage collected without patching, see spl/u-boot-spl.map after
building.  So again I say, if common/serial.o is NOT being discard in
your series on m28evk there is a bug in your series to fix or a change
to better understand and document (and then see if we can change since
as Scott notes, this needs to work for 4kb boards and that is tight).

- -- 
Tom
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