On the xscale, the icache must be invalidated and the write buffers drained after writing code over the data bus, even if the caches are disabled. After rebasing with the main git repository, u-boot began crashing in odd places on my pxa270 board (palmtreo680) after the code relocation routine ran. This patch fixes it. Cache coherency problems are often hit-and-miss (ha ha), and this latent problem didn't rear its ugly head until now. Tested on the pxa270.
Signed-off-by: Mike Dunn mikedunn@newsguy.com ---
I realize that __ARM_ARCH_5TE__ does not necessarily mean xscale. But how else to test for pxa2xx/ixp in an assembly file? I wouldn't expect any ill effects on a non-xscale v5te because these CP15 operations are defined the same way in the ARM Architecture Reference Manual for v5 cores, but unfortunately I only have a pxa270 xscale to test on.
I experienced this same problem a couple years ago when I was getting OpenOCD working on the xscale. Often software breakpoints (replacing an instruction with the 'bkpt' instruction) would fail unless this operation was performed after replacing the instruction, even with caches off. The following two paragraphs are cut from section 4.2.7 of the xscale core developer's manual...
If the instruction cache is not enabled, or code is being written to a non-cacheable region, software must still invalidate the instruction cache before using the newly-written code. This precaution ensures that state associated with the new code is not buffered elsewhere in the processor, such as the fetch buffers or the BTB.
Naturally, when writing code as data, care must be taken to force it completely out of the processor into external memory before attempting to execute it. If writing into a non-cacheable region, flushing the write buffers is sufficient precaution (see Section 7.2.8 for a description of this
arch/arm/lib/relocate.S | 10 ++++++++++ 1 files changed, 10 insertions(+), 0 deletions(-)
diff --git a/arch/arm/lib/relocate.S b/arch/arm/lib/relocate.S index 4446da9..e2febed 100644 --- a/arch/arm/lib/relocate.S +++ b/arch/arm/lib/relocate.S @@ -92,6 +92,16 @@ fixnext:
relocate_done:
+#ifdef __ARM_ARCH_5TE__ + /* + * On xscale, icache must be invalidated and write buffers drained, + * even with cache disabled - 4.2.7 of xscale core developer's manual + */ + mov r0, #0 /* arm reference manual: "data SBZ" */ + mcr p15, 0, r0, c7, c7, 0 /* invalidate icache */ + mcr p15, 0, r0, c7, c10, 4 /* drain write buffer */ +#endif + /* ARMv4- don't know bx lr but the assembler fails to see that */
#ifdef __ARM_ARCH_4__