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authorGabor Juhos <juhosg@openwrt.org>2011-11-13 11:26:52 +0000
committerGabor Juhos <juhosg@openwrt.org>2011-11-13 11:26:52 +0000
commit0112153a0eecfd08dfe6aa80d68120d14476fe95 (patch)
tree503bd354f90c2fdd8d33e8bf744defe121bf046c /target
parent1afc76ea130bdfa8991329da124fe966eab4228d (diff)
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ar71xx: fix occasional kernel hangs during boot on AR934x
The patch taken from the linux-mips mailing list. The Kernel hangs occasionally during boot after "Calibrating delay loop..". This is caused by the c0_compare_int_usable() routine in cevt-r4k.c returning false which causes the system to disable the timer and hang later. The false return happens because the routine is using a series of four calls to irq_disable_hazard() as a delay while it waits for the timer changes to propagate to the cp0 cause register. On newer MIPS cores, like the 74K, the series of irq_disable_hazard() calls turn into ehb instructions and can take as little as a few clock ticks for all 4 instructions. This is not enough of a delay, so the routine thinks the timer is not working. This fix uses up to a max number of cycle counter ticks for the delay and uses back_to_back_c0_hazard() instead of irq_disable_hazard() to handle the hazard condition between cp0 writes and cp0 reads. SVN-Revision: 29009
Diffstat (limited to 'target')
-rw-r--r--target/linux/ar71xx/patches-2.6.39/902-fix-occasional-kernel-hangs-during-boot.patch104
1 files changed, 104 insertions, 0 deletions
diff --git a/target/linux/ar71xx/patches-2.6.39/902-fix-occasional-kernel-hangs-during-boot.patch b/target/linux/ar71xx/patches-2.6.39/902-fix-occasional-kernel-hangs-during-boot.patch
new file mode 100644
index 0000000000..8150ee4810
--- /dev/null
+++ b/target/linux/ar71xx/patches-2.6.39/902-fix-occasional-kernel-hangs-during-boot.patch
@@ -0,0 +1,104 @@
+From patchwork Tue Nov 8 14:59:01 2011
+Content-Type: text/plain; charset="utf-8"
+MIME-Version: 1.0
+Content-Transfer-Encoding: 7bit
+Subject: MIPS: Kernel hangs occasionally during boot.
+Date: Tue, 08 Nov 2011 13:59:01 -0000
+From: Al Cooper <alcooperx@gmail.com>
+X-Patchwork-Id: 2911
+Message-Id: <1320764341-4275-1-git-send-email-alcooperx@gmail.com>
+To: ralf@linux-mips.org, linux-mips@linux-mips.org,
+ linux-kernel@vger.kernel.org
+Cc: "Al Cooper" <alcooperx@gmail.com>
+
+The Kernel hangs occasionally during boot after
+"Calibrating delay loop..". This is caused by the
+c0_compare_int_usable() routine in cevt-r4k.c returning false which
+causes the system to disable the timer and hang later. The false
+return happens because the routine is using a series of four calls to
+irq_disable_hazard() as a delay while it waits for the timer changes
+to propagate to the cp0 cause register. On newer MIPS cores, like the 74K,
+the series of irq_disable_hazard() calls turn into ehb instructions and
+can take as little as a few clock ticks for all 4 instructions. This
+is not enough of a delay, so the routine thinks the timer is not working.
+This fix uses up to a max number of cycle counter ticks for the delay
+and uses back_to_back_c0_hazard() instead of irq_disable_hazard() to
+handle the hazard condition between cp0 writes and cp0 reads.
+
+Signed-off-by: Al Cooper <alcooperx@gmail.com>
+
+---
+arch/mips/kernel/cevt-r4k.c | 38 +++++++++++++++++++-------------------
+ 1 files changed, 19 insertions(+), 19 deletions(-)
+
+--- a/arch/mips/kernel/cevt-r4k.c
++++ b/arch/mips/kernel/cevt-r4k.c
+@@ -103,19 +103,10 @@ static int c0_compare_int_pending(void)
+
+ /*
+ * Compare interrupt can be routed and latched outside the core,
+- * so a single execution hazard barrier may not be enough to give
+- * it time to clear as seen in the Cause register. 4 time the
+- * pipeline depth seems reasonably conservative, and empirically
+- * works better in configurations with high CPU/bus clock ratios.
++ * so wait up to worst case number of cycle counter ticks for timer interrupt
++ * changes to propagate to the cause register.
+ */
+-
+-#define compare_change_hazard() \
+- do { \
+- irq_disable_hazard(); \
+- irq_disable_hazard(); \
+- irq_disable_hazard(); \
+- irq_disable_hazard(); \
+- } while (0)
++#define COMPARE_INT_SEEN_TICKS 50
+
+ int c0_compare_int_usable(void)
+ {
+@@ -126,8 +117,12 @@ int c0_compare_int_usable(void)
+ * IP7 already pending? Try to clear it by acking the timer.
+ */
+ if (c0_compare_int_pending()) {
+- write_c0_compare(read_c0_count());
+- compare_change_hazard();
++ cnt = read_c0_count();
++ write_c0_compare(cnt);
++ back_to_back_c0_hazard();
++ while (read_c0_count() < (cnt + COMPARE_INT_SEEN_TICKS))
++ if (!c0_compare_int_pending())
++ break;
+ if (c0_compare_int_pending())
+ return 0;
+ }
+@@ -136,7 +131,7 @@ int c0_compare_int_usable(void)
+ cnt = read_c0_count();
+ cnt += delta;
+ write_c0_compare(cnt);
+- compare_change_hazard();
++ back_to_back_c0_hazard();
+ if ((int)(read_c0_count() - cnt) < 0)
+ break;
+ /* increase delta if the timer was already expired */
+@@ -145,12 +140,17 @@ int c0_compare_int_usable(void)
+ while ((int)(read_c0_count() - cnt) <= 0)
+ ; /* Wait for expiry */
+
+- compare_change_hazard();
++ while (read_c0_count() < (cnt + COMPARE_INT_SEEN_TICKS))
++ if (c0_compare_int_pending())
++ break;
+ if (!c0_compare_int_pending())
+ return 0;
+-
+- write_c0_compare(read_c0_count());
+- compare_change_hazard();
++ cnt = read_c0_count();
++ write_c0_compare(cnt);
++ back_to_back_c0_hazard();
++ while (read_c0_count() < (cnt + COMPARE_INT_SEEN_TICKS))
++ if (!c0_compare_int_pending())
++ break;
+ if (c0_compare_int_pending())
+ return 0;
+