OMAP2/3: SRAM: add comment about crashes during a TLB miss

Some users were observing crashes during the execution of CORE DVFS
code from OCM RAM -- a locally-modified copy of the linux-omap code.
Richard Woodruff tracked this down to a DTLB miss which had been
inadvertently and intermittently caused by the local modifications.
(The TLB miss caused the ARM MMU to attempt to walk the page tables
stored in SDRAM, which was not possible since SDRAM is off-line for a
portion of the CORE DVFS OCM RAM code.)

Add a note to the OMAP2 & OMAP3 CORE DVFS SRAM code to warn others that
changes may result in crashes here if they are not carefully tested.

Signed-off-by: Paul Walmsley <paul@pwsan.com>
Cc: Richard Woodruff <r-woodruff2@ti.com>
Cc: Jon Hunter <jon-hunter@ti.com>
Cc: Nishanth Menon <nm@ti.com>

diff --git a/arch/arm/mach-omap2/sram242x.S b/arch/arm/mach-omap2/sram242x.S
index 8e7e6fef09efde02564680abbc35e5718d747491..055310cc77decbbd2c454ec08d40dbc0323e643c 100644 (file)
--- a/arch/arm/mach-omap2/sram242x.S
+++ b/arch/arm/mach-omap2/sram242x.S
@@ -21,6 +21,12 @@
  * along with this program; if not, write to the Free Software
  * Foundation, Inc., 59 Temple Place, Suite 330, Boston,
  * MA 02111-1307 USA
+ *
+ * Richard Woodruff notes that any changes to this code must be carefully
+ * audited and tested to ensure that they don't cause a TLB miss while
+ * the SDRAM is inaccessible.  Such a situation will crash the system
+ * since it will cause the ARM MMU to attempt to walk the page tables.
+ * These crashes may be intermittent.
  */
 #include <linux/linkage.h>
 #include <asm/assembler.h>

diff --git a/arch/arm/mach-omap2/sram243x.S b/arch/arm/mach-omap2/sram243x.S
index 9ea87f68524f69128e7b660582d62fd5b2fb786f..f9007580aea344c2f264ae55fde119b187f68b0f 100644 (file)
--- a/arch/arm/mach-omap2/sram243x.S
+++ b/arch/arm/mach-omap2/sram243x.S
@@ -21,6 +21,12 @@
  * along with this program; if not, write to the Free Software
  * Foundation, Inc., 59 Temple Place, Suite 330, Boston,
  * MA 02111-1307 USA
+ *
+ * Richard Woodruff notes that any changes to this code must be carefully
+ * audited and tested to ensure that they don't cause a TLB miss while
+ * the SDRAM is inaccessible.  Such a situation will crash the system
+ * since it will cause the ARM MMU to attempt to walk the page tables.
+ * These crashes may be intermittent.
  */
 #include <linux/linkage.h>
 #include <asm/assembler.h>

diff --git a/arch/arm/mach-omap2/sram34xx.S b/arch/arm/mach-omap2/sram34xx.S
index b7aba60f832528d8bd5af844d4feccbe116c994e..7f893a29d5005052d60c0493c5a37960b71b0ce2 100644 (file)
--- a/arch/arm/mach-omap2/sram34xx.S
+++ b/arch/arm/mach-omap2/sram34xx.S
@@ -104,6 +104,12 @@
  * touching the SDRAM.  Until that time, users who know that their use case
  * can satisfy the above requirement can enable the CONFIG_OMAP3_SDRC_AC_TIMING
  * option.
+ *
+ * Richard Woodruff notes that any changes to this code must be carefully
+ * audited and tested to ensure that they don't cause a TLB miss while
+ * the SDRAM is inaccessible.  Such a situation will crash the system
+ * since it will cause the ARM MMU to attempt to walk the page tables.
+ * These crashes may be intermittent.
  */
 ENTRY(omap3_sram_configure_core_dpll)
        stmfd   sp!, {r1-r12, lr}       @ store regs to stack