Add the qualcomm minidump guide for the users which
tries to cover the dependency and the way to test
and collect minidump on Qualcomm supported platforms.
Signed-off-by: Mukesh Ojha <quic_mojha@xxxxxxxxxxx>
---
Documentation/admin-guide/qcom_minidump.rst | 240 ++++++++++++++++++++++++++++
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create mode 100644 Documentation/admin-guide/qcom_minidump.rst
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+Qualcomm Minidump Feature
+=========================
+
+Introduction
+------------
+
+Minidump is a best effort mechanism to collect useful and predefined
+data for first level of debugging on end user devices running on
+Qualcomm SoCs. It is built on the premise that System on Chip (SoC)
+or subsystem part of SoC crashes, due to a range of hardware and
+software bugs. Hence, the ability to collect accurate data is only
+a best-effort. The data collected could be invalid or corrupted, data
+collection itself could fail, and so on.
+
+Qualcomm devices in engineering mode provides a mechanism for generating
+full system ramdumps for post mortem debugging. But in some cases it's
+however not feasible to capture the entire content of RAM. The minidump
+mechanism provides the means for selecting region should be included in
+the ramdump.
+
+::
+
+ +-----------------------------------------------+
+ | DDR +-------------+ |
+ | | SS0-ToC| |
+ | +----------------+ +----------------+ | |
+ | |Shared memory | | SS1-ToC| | |
+ | |(SMEM) | | | | |
+ | | | +-->|--------+ | | |
+ | |G-ToC | | | SS-ToC \ | | |
+ | |+-------------+ | | | +-----------+ | | |
+ | ||-------------| | | | |-----------| | | |
+ | || SS0-ToC | | | +-|<|SS1 region1| | | |
+ | ||-------------| | | | | |-----------| | | |
+ | || SS1-ToC |-|>+ | | |SS1 region2| | | |
+ | ||-------------| | | | |-----------| | | |
+ | || SS2-ToC | | | | | ... | | | |
+ | ||-------------| | | | |-----------| | | |
+ | || ... | | |-|<|SS1 regionN| | | |
+ | ||-------------| | | | |-----------| | | |
+ | || SSn-ToC | | | | +-----------+ | | |
+ | |+-------------+ | | | | | |
+ | | | | |----------------| | |
+ | | | +>| regionN | | |
+ | | | | |----------------| | |
+ | +----------------+ | | | | |
+ | | |----------------| | |
+ | +>| region1 | | |
+ | |----------------| | |
+ | | | | |
+ | |----------------|-+ |
+ | | region5 | |
+ | |----------------| |
+ | | | |
+ | Region information +----------------+ |
+ | +---------------+ |
+ | |region name | |
+ | |---------------| |
+ | |region address | |
+ | |---------------| |
+ | |region size | |
+ | +---------------+ |
+ +-----------------------------------------------+
+ G-ToC: Global table of content
+ SS-ToC: Subsystem table of content
+ SS0-SSn: Subsystem numbered from 0 to n
+
+The core of minidump feature is part of Qualcomm's boot firmware code.
+It initializes shared memory(SMEM), which is a part of DDR and
+allocates a small section of it to minidump table i.e also called
+global table of content (G-ToC). Each subsystem (APSS, ADSP, ...) has
+their own table of segments to be included in the minidump, all
+references from a descriptor in SMEM (G-ToC). Each segment/region has
+some details like name, physical address and it's size etc. and it
+could be anywhere scattered in the DDR.
+
+Minidump kernel driver concept
+------------------------------
+
+Qualcomm minidump kernel driver adds the capability to add linux region
+to be dumped as part of ram dump collection. It provides appropriate
+symbol to check its enablement and register client region.
+
+To simplify post mortem debugging, it creates and maintain an ELF
+header as first region that gets updated each time a new region gets
+registered.
+
+The solution supports extracting the ramdump/minidump produced either
+over USB or stored to an attached storage device.
+
+Dependency of minidump kernel driver
+------------------------------------
+
+It is noted that minidump kernel driver depends on Qualcomm's
+shared memory (SMEM) driver and its device tree entry (device
+presence). If above support is present and Qualcomm boot firmware
+has minidump support, so it is possible to dump linux region as
+part of minidump collection.
+
+How a kernel client driver can register region with minidump
+------------------------------------------------------------
+
+Client driver can use qcom_minidump_ready() symbol to check if the
+minidump driver is supported on the target and if it return -ENODEV
+then it means minidump is not supported on this target and the client
+should not try to register their minidump region further and
+continue with their normal execution, and if it is supported it
+can go ahead register its region with qcom_minidump_region_register().
+
+Client need to fill their region by filling qcom_minidump_region
+structure object which consist of the region name, region's
+virtual and physical address and its size.
+
+Below is one sample client driver snippet which try to allocate
+a region from kernel heap of certain size and it writes a certain
+known pattern (that can help in verification after collection
+that we got the exact pattern, what we wrote) and registers with
+minidump.
+
+ .. code-block:: c
+
+ #include <soc/qcom/minidump.h>
+ [...]
+
+
+ [... inside a function ...]
+ struct qcom_minidump_region region;
+
+ [...]
+
+ client_mem_region = kzalloc(region_size, GFP_KERNEL);
+ if (!client_mem_region)
+ return -ENOMEM;
+
+ [... Just write a pattern ...]
+ memset(client_mem_region, 0xAB, region_size);
+
+ [... Check if minidump is ready return -EPROBE_DEFER
+ if this is a probe function otherwise return accordingly ...]
+ err = qcom_minidump_ready();
+ if (err && err != -ENODEV)
+ return -EPROBE_DEFER;
+
+ strlcpy(region.name, "REGION_A", sizeof(region.name));
+ region.virt_addr = client_mem_region;
+ region.phys_addr = virt_to_phys(client_mem_region);
+ region.size = region_size;
+
+ if (!err) {
+ ret = qcom_minidump_region_register(®ion);
+ if (ret < 0) {
+ pr_err("failed to add region in minidump: err: %d\n", ret);
+ return ret;
+ }
+ }
+
+ [...]
+
+
+Test
+----
+
+Existing Qualcomm devices already supports entire ddr dump (also called
+full dump) via writing appropriate value to Qualcomm's top control and
+status register(tcsr) in driver/firmware/qcom_scm.c .
+
+SCM device Tree bindings required to support download mode
+For example (sm8450) ::
+
+ / {
+
+ [...]
+
+ firmware {
+ scm: scm {
+ compatible = "qcom,scm-sm8450", "qcom,scm";
+ [... tcsr register ... ]
+ qcom,dload-mode = <&tcsr 0x13000>;
+
+ [...]
+ };
+ };
+
+ [...]
+
+ soc: soc@0 {
+
+ [...]
+
+ tcsr: syscon@1fc0000 {
+ compatible = "qcom,sm8450-tcsr", "syscon";
+ reg = <0x0 0x1fc0000 0x0 0x30000>;
+ };
+
+ [...]
+ };
+ [...]
+
+ };
+
+User of minidump can pass qcom_scm.download_mode="mini" to kernel
+commandline to set the current download mode to minidump.
+
+Similarly, "full" is passed to set the download mode to full dump
+where entire ddr dump will be collected while setting it "both"
+will set the mode to both (mini + full).
+
+sysfs can also be used to set the mode to minidump.
+
+::
+ echo "mini" > /sys/module/qcom_scm/parameter/download_mode
+
+Once the download mode is set, any kind of crash will make the device collect
+respective dump as per set download mode.
+
+Dump collection
+---------------
+
+The solution supports extracting the minidump produced either over USB or
+stored to an attached storage device.
+
+By default, dumps are downloaded via USB to the attached x86_64 machine
+running PCAT (Qualcomm tool) software. Upon download, we will see
+a set of binary blobs starts with name md_* in PCAT configured directory
+in x86_64 machine, so for above example from the client it will be
+md_REGION_A.BIN. This binary blob depends on region content to determine
+whether it needs external parser support to get the content of the region,
+so for simple plain ASCII text we don't need any parsing and the content
+can be seen just opening the binary file.
+
+To collect the dump to attached storage type, one need to write appropriate
+value to IMEM register, in that case dumps are collected in rawdump
+partition on the target device itself.
+
+One need to read the entire rawdump partition and pull out content to
+save it onto the attached x86_64 machine over USB. Later, this rawdump
+can be pass it to another tool dexter.exe(Qualcomm tool) which converts
+this into the similar binary blobs which we have got it when download type
+was set to USB i.e a set of registered region as blobs and their name
+starts with md_*.
--
2.7.4
