From cba4b1809f043bf85c806e5a4e342f62bd5ded45 Mon Sep 17 00:00:00 2001 From: Aneesh V Date: Tue, 16 Aug 2011 04:33:05 +0000 Subject: arm: do not force d-cache enable on all boards c2dd0d45540397704de9b13287417d21049d34c6 added dcache_enable() to board_init_r(). This enables d-cache for all ARM boards. As a result some of the arm boards that are not cache-ready are broken. Revert this change and allow platform code to take the decision on d-cache enabling. Also add some documentation for cache usage in ARM. Signed-off-by: Aneesh V --- doc/README.arm-caches | 51 +++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 51 insertions(+) create mode 100644 doc/README.arm-caches (limited to 'doc/README.arm-caches') diff --git a/doc/README.arm-caches b/doc/README.arm-caches new file mode 100644 index 0000000..cd2b458 --- /dev/null +++ b/doc/README.arm-caches @@ -0,0 +1,51 @@ +Disabling I-cache: +- Set CONFIG_SYS_ICACHE_OFF + +Disabling D-cache: +- Set CONFIG_SYS_DCACHE_OFF + +Enabling I-cache: +- Make sure CONFIG_SYS_ICACHE_OFF is not set and call icache_enable(). + +Enabling D-cache: +- Make sure CONFIG_SYS_DCACHE_OFF is not set and call dcache_enable(). + +Enabling Caches at System Startup: +- Implement enable_caches() for your platform and enable the I-cache and + D-cache from this function. This function is called immediately + after relocation. + +Guidelines for Working with D-cache: + +Memory to Peripheral DMA: +- Flush the buffer after the MPU writes the data and before the DMA is + initiated. + +Peripheral to Memory DMA: +- Invalidate the buffer before starting the DMA. In case there are any dirty + lines from the DMA buffer in the cache, subsequent cache-line replacements + may corrupt the buffer in memory while the DMA is still going on. Cache-line + replacement can happen if the CPU tries to bring some other memory locations + into the cache while the DMA is going on. +- Invalidate the buffer after the DMA is complete and before the MPU reads + it. This may be needed in addition to the invalidation before the DMA + mentioned above, because in some processors memory contents can spontaneously + come to the cache due to speculative memory access by the CPU. If this + happens with the DMA buffer while DMA is going on we have a coherency problem. + +Buffer Requirements: +- Any buffer that is invalidated(that is, typically the peripheral to + memory DMA buffer) should be aligned to cache-line boundary both at + at the beginning and at the end of the buffer. +- If the buffer is not cache-line aligned invalidation will be restricted + to the aligned part. That is, one cache-line at the respective boundary + may be left out while doing invalidation. + +Cleanup Before Linux: +- cleanup_before_linux() should flush the D-cache, invalidate I-cache, and + disable MMU and caches. +- The following sequence is advisable while disabling d-cache: + 1. disable_dcache() - flushes and disables d-cache + 2. invalidate_dcache_all() - invalid any entry that came to the cache + in the short period after the cache was flushed but before the + cache got disabled. -- cgit v1.1