path: root/Documentation
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authorLinus Torvalds <torvalds@linux-foundation.org>2014-12-12 11:34:13 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2014-12-12 11:34:13 -0800
commit6ce4436c9cbe903af935291aa219fd6f4c85722d (patch)
tree43dedf78042c619d8b5b0a77d6937eb22805d874 /Documentation
parentMerge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/mason/linux-btrfs (diff)
parentpstore-ram: Allow optional mapping with pgprot_noncached (diff)
Merge tag 'please-pull-morepstore' of git://git.kernel.org/pub/scm/linux/kernel/git/aegl/linux
Pull pstore update #2 from Tony Luck: "Couple of pstore-ram enhancements to allow use of different memory attributes" * tag 'please-pull-morepstore' of git://git.kernel.org/pub/scm/linux/kernel/git/aegl/linux: pstore-ram: Allow optional mapping with pgprot_noncached pstore-ram: Fix hangs by using write-combine mappings
Diffstat (limited to 'Documentation')
1 files changed, 11 insertions, 2 deletions
diff --git a/Documentation/ramoops.txt b/Documentation/ramoops.txt
index 69b3cac4749d..5d8675615e59 100644
--- a/Documentation/ramoops.txt
+++ b/Documentation/ramoops.txt
@@ -14,11 +14,19 @@ survive after a restart.
1. Ramoops concepts
-Ramoops uses a predefined memory area to store the dump. The start and size of
-the memory area are set using two variables:
+Ramoops uses a predefined memory area to store the dump. The start and size
+and type of the memory area are set using three variables:
* "mem_address" for the start
* "mem_size" for the size. The memory size will be rounded down to a
power of two.
+ * "mem_type" to specifiy if the memory type (default is pgprot_writecombine).
+Typically the default value of mem_type=0 should be used as that sets the pstore
+mapping to pgprot_writecombine. Setting mem_type=1 attempts to use
+pgprot_noncached, which only works on some platforms. This is because pstore
+depends on atomic operations. At least on ARM, pgprot_noncached causes the
+memory to be mapped strongly ordered, and atomic operations on strongly ordered
+memory are implementation defined, and won't work on many ARMs such as omaps.
The memory area is divided into "record_size" chunks (also rounded down to
power of two) and each oops/panic writes a "record_size" chunk of
@@ -55,6 +63,7 @@ Setting the ramoops parameters can be done in 2 different manners:
static struct ramoops_platform_data ramoops_data = {
.mem_size = <...>,
.mem_address = <...>,
+ .mem_type = <...>,
.record_size = <...>,
.dump_oops = <...>,
.ecc = <...>,