On Fri, 20 Feb 2015, Matt Turner wrote:
> On Fri, Feb 20, 2015 at 8:00 PM, Matt Turner <mattst88@xxxxxxxxx> wrote:
> > On Fri, Feb 20, 2015 at 1:53 AM, Robert P. J. Day <rpjday@xxxxxxxxxxxxxx> wrote:
> >>
> >> was recently handed a MIPS-based dev board (can't name the vendor,
> >> NDA) that *typically* runs in LE mode but, because of a proprietary
> >> binary that must be run on the board and was compiled as BE, has to be
> >> run in BE mode.
> >>
> >> the vendor supplied a yoctoproject layer that seems to work fine
> >> but, in changing the DEFAULTTUNE to big-endian, the following patch
> >> had to be applied to the 3.14 kernel tree to the file
> >> arch/mips/include/asm/io.h in order to get output from the console
> >> port as the system was booting:
> >>
> >> 326c326,333
> >> < *__mem = __val; \
> >> ---
> >>> { \
> >>> if (sizeof(type) == sizeof(u32)) \
> >>> { \
> >>> *__mem = __cpu_to_le32(__val); \
> >
> > They're byte swapping a value if they're in big endian mode.
> >
> >>> } \
> >>> else \
> >>> *__mem = __val; \
> >
> > And they don't seem to really understand the __cpu_to_le32 macro...
>
> Sorry, I should be more precise. They're byte swapping 32-bit values
> if they're in big endian mode, and copying everything else without
> conversion.
i understand *in general* what the above is doing ... what i don't
understand is why it's necessary to hack a fundamental kernel header
file this way in order to run this board in BE versus LE mode.
the kernel was already configured for BE mode, which i would have
thought would be sufficient, so it's a mystery to me why one would
still have to *further* hack the io.h file this way -- if the above is
a necessity, shouldn't it be a conditional change based on selecting
BE configuration?
has anyone else ever needed to do this? or is this some weird,
one-off hack that perhaps applies *only* to some bizarre feature of
this board?
rday
--
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Robert P. J. Day Ottawa, Ontario, CANADA
http://crashcourse.ca
Twitter: http://twitter.com/rpjday
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