diff options
authoraneeshv <aneesh@ti.com>2011-08-11 04:35:42 +0000
committerJohn Rigby <john.rigby@linaro.org>2011-08-24 07:10:49 -0600
commitc2166e2481a537d593b5ab1bf347ba6ca1ca4278 (patch)
parent74a88dcd51d09dcb3812f9ebdc2738184c71995b (diff)
arm: do not force d-cache enable on all boards2011.08.5
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 <aneesh@ti.com>
4 files changed, 67 insertions, 5 deletions
diff --git a/arch/arm/lib/board.c b/arch/arm/lib/board.c
index 14a56f6f0..38a31d82b 100644
--- a/arch/arm/lib/board.c
+++ b/arch/arm/lib/board.c
@@ -451,11 +451,9 @@ void board_init_r(gd_t *id, ulong dest_addr)
gd->flags |= GD_FLG_RELOC; /* tell others: relocation done */
monitor_flash_len = _end_ofs;
- /*
- * Enable D$:
- * I$, if needed, must be already enabled in start.S
- */
- dcache_enable();
+ /* Enable caches */
+ enable_caches();
debug("monitor flash len: %08lX\n", monitor_flash_len);
board_init(); /* Setup chipselects */
diff --git a/arch/arm/lib/cache.c b/arch/arm/lib/cache.c
index 92b61a265..b545fb79b 100644
--- a/arch/arm/lib/cache.c
+++ b/arch/arm/lib/cache.c
@@ -53,3 +53,15 @@ void __flush_dcache_all(void)
void flush_dcache_all(void)
__attribute__((weak, alias("__flush_dcache_all")));
+ * Default implementation of enable_caches()
+ * Real implementation should be in platform code
+ */
+void __enable_caches(void)
+ puts("WARNING: Caches not enabled\n");
+void enable_caches(void)
+ __attribute__((weak, alias("__enable_caches")));
diff --git a/doc/README.arm-caches b/doc/README.arm-caches
new file mode 100644
index 000000000..a833eeefa
--- /dev/null
+++ b/doc/README.arm-caches
@@ -0,0 +1,51 @@
+Disabling I-cache:
+Disabling D-cache:
+Enabling I-cache:
+- Make sure CONFIG_SYS_ICACHE_OFF is not set and call icache_enable().
+Enabling D-cache:
+- Make sure CONFIG_SYS_ICACHE_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.
diff --git a/include/common.h b/include/common.h
index 0c4a91e0a..cb3599652 100644
--- a/include/common.h
+++ b/include/common.h
@@ -623,6 +623,7 @@ ulong lcd_setmem (ulong);
ulong video_setmem (ulong);
/* arch/$(ARCH)/lib/cache.c */
+void enable_caches(void);
void flush_cache (unsigned long, unsigned long);
void flush_dcache_all(void);
void flush_dcache_range(unsigned long start, unsigned long stop);