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); \
>> } \
>> else \
>> *__mem = __val; \
>> } \
> 356a364
>> { \
> 357a366,368
>> if (sizeof(type) == sizeof(u32)) \
>> __val = __cpu_to_le32(__val); \
>> } \
>
> without that patch, the initial conclusion was that the board was
> just hanging at boot, but i was told, no, it was booting, there was
> just no output at the console port. applied the patch and, voila.
If it's using the serial8250 driver with a standard 16550A-ish UART,
MMIO accesses via readl()/writel() may be byteswapped on a BE system.
Historically I've dealt with this problem by locally modifying the
serial8250 driver to use the __raw_* variants, but here is a patch
that lets you instruct the driver to use either LE or BE accessors:
http://patchwork.linux-mips.org/patch/8572/
