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authorTony Lindgren <tony@atomide.com>2014-09-16 20:50:01 (GMT)
committerTony Luck <tony.luck@intel.com>2014-12-11 21:38:31 (GMT)
commit027bc8b08242c59e19356b4b2c189f2d849ab660 (patch)
tree4bd5ad81fef12692af2c9d278f14903d15ddfb60 /Documentation/ramoops.txt
parent7ae9cb81933515dc7db1aa3c47ef7653717e3090 (diff)
pstore-ram: Allow optional mapping with pgprot_noncached
On some ARMs the memory can be mapped pgprot_noncached() and still be working for atomic operations. As pointed out by Colin Cross <ccross@android.com>, in some cases you do want to use pgprot_noncached() if the SoC supports it to see a debug printk just before a write hanging the system. On ARMs, the atomic operations on strongly ordered memory are implementation defined. So let's provide an optional kernel parameter for configuring pgprot_noncached(), and use pgprot_writecombine() by default. Cc: Arnd Bergmann <arnd@arndb.de> Cc: Rob Herring <robherring2@gmail.com> Cc: Randy Dunlap <rdunlap@infradead.org> Cc: Anton Vorontsov <anton@enomsg.org> Cc: Colin Cross <ccross@android.com> Cc: Olof Johansson <olof@lixom.net> Cc: Russell King <linux@arm.linux.org.uk> Cc: stable@vger.kernel.org Acked-by: Kees Cook <keescook@chromium.org> Signed-off-by: Tony Lindgren <tony@atomide.com> Signed-off-by: Tony Luck <tony.luck@intel.com>
Diffstat (limited to 'Documentation/ramoops.txt')
-rw-r--r--Documentation/ramoops.txt13
1 files changed, 11 insertions, 2 deletions
diff --git a/Documentation/ramoops.txt b/Documentation/ramoops.txt
index 69b3cac..5d86756 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 = <...>,

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