doc: move pstore.rst to usage/pstore.rst

Let's have a separate chapter dedicated to using U-Boot.

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>

2 files changed, 94 insertions, 0 deletions

diff --git a/doc/usage/index.rst b/doc/usage/index.rst
new file mode 100644
index 00000000000..af7d50650df
--- /dev/null
+++ b/doc/usage/index.rst
@@ -0,0 +1,12 @@
+Use U-Boot
+==========
+
+.. toctree::
+
+Shell commands
+--------------
+
+.. toctree::
+   :maxdepth: 1
+
+   pstore
diff --git a/doc/usage/pstore.rst b/doc/usage/pstore.rst
new file mode 100644
index 00000000000..8427d8fd97a
--- /dev/null
+++ b/doc/usage/pstore.rst
@@ -0,0 +1,82 @@
+.. SPDX-License-Identifier: GPL-2.0+
+
+PStore command
+==============
+
+Design
+------
+
+Linux PStore and Ramoops modules (Linux config options PSTORE and PSTORE_RAM)
+allow to use memory to pass data from the dying breath of a crashing kernel to
+its successor. This command allows to read those records from U-Boot command
+line.
+
+Ramoops is an oops/panic logger that writes its logs to RAM before the system
+crashes. It works by logging oopses and panics in a circular buffer. Ramoops
+needs a system with persistent RAM so that the content of that area can survive
+after a restart.
+
+Ramoops uses a predefined memory area to store the dump.
+
+Ramoops parameters can be passed as kernel parameters or through Device Tree,
+i.e.::
+
+    ramoops.mem_address=0x30000000 ramoops.mem_size=0x100000 ramoops.record_size=0x2000 ramoops.console_size=0x2000 memmap=0x100000$0x30000000
+
+The same values should be set in U-Boot to be able to retrieve the records.
+This values can be set at build time in U-Boot configuration file, or at runtime.
+U-Boot automatically patches the Device Tree to pass the Ramoops parameters to
+the kernel.
+
+The PStore configuration parameters are:
+
+======================= ==========
+ Name                   Default
+======================= ==========
+CMD_PSTORE_MEM_ADDR
+CMD_PSTORE_MEM_SIZE     0x10000
+CMD_PSTORE_RECORD_SIZE  0x1000
+CMD_PSTORE_CONSOLE_SIZE 0x1000
+CMD_PSTORE_FTRACE_SIZE  0x1000
+CMD_PSTORE_PMSG_SIZE    0x1000
+CMD_PSTORE_ECC_SIZE     0
+======================= ==========
+
+Records sizes should be a power of 2.
+The memory size and the record/console size must be non-zero.
+
+Multiple 'dump' records can be stored in the memory reserved for PStore.
+The memory size has to be larger than the sum of the record sizes, i.e.::
+
+    MEM_SIZE >= RECORD_SIZE * n + CONSOLE_SIZE + FTRACE_SIZE + PMSG_SIZE
+
+Usage
+-----
+
+Generate kernel crash
+~~~~~~~~~~~~~~~~~~~~~
+
+For test purpose, you can generate a kernel crash by setting reboot timeout to
+10 seconds and trigger a panic::
+
+    $ sudo sh -c "echo 1 > /proc/sys/kernel/sysrq"
+    $ sudo sh -c "echo 10 > /proc/sys/kernel/panic"
+    $ sudo sh -c "echo c > /proc/sysrq-trigger"
+
+Retrieve logs in U-Boot
+~~~~~~~~~~~~~~~~~~~~~~~
+
+First of all, unless PStore parameters as been set during U-Boot configuration
+and match kernel ramoops parameters, it needs to be set using 'pstore set', e.g.::
+
+    => pstore set 0x30000000 0x100000 0x2000 0x2000
+
+Then all available dumps can be displayed
+using::
+
+    => pstore display
+
+Or saved to an existing directory in an Ext2 or Ext4 partition, e.g. on root
+directory of 1st partition of the 2nd MMC::
+
+    => pstore save mmc 1:1 /