On 5/14/2023 12:16 AM, Randy Dunlap wrote:

On 5/3/23 10:02, Mukesh Ojha wrote:

quoted

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 <redacted>
---
  Documentation/admin-guide/qcom_minidump.rst | 246 ++++++++++++++++++++++++++++
  1 file changed, 246 insertions(+)
  create mode 100644 Documentation/admin-guide/qcom_minidump.rst

diff --git a/Documentation/admin-guide/qcom_minidump.rst b/Documentation/admin-guide/qcom_minidump.rst
new file mode 100644
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@@ -0,0 +1,246 @@
+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

                RAM dumps for {post-mortem or postmortem} debugging.

quoted

+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

                                  contents
?

quoted

+       SS-ToC: Subsystem table of content

                                      contents
?

quoted

+       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

                          memory (SMEM),

quoted

+allocates a small section of it to minidump table i.e also called

                                                table, i.e.

quoted

+global table of content (G-ToC). Each subsystem (APSS, ADSP, ...) has

                    contents

quoted

+their own table of segments to be included in the minidump, all

    its own table

quoted

+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

                                                 its

quoted

+could be anywhere scattered in the DDR.
+
+Minidump kernel driver concept
+------------------------------
+
+Qualcomm minidump kernel driver adds the capability to add linux region

                                                               Linux

quoted

+to be dumped as part of ram dump collection. At the moment, shared memory

                            RAM

quoted

+driver creates plaform device for minidump driver and give a means to

                   platform

quoted

+APSS minidump to initialize itself on probe.
+
+This driver provides ``qcom_apss_minidump_region_register`` and
+``qcom_apss_minidump_region_unregister`` API's to register and unregister
+apss minidump region. It also gives a mechanism to update physical/virtual

    APSS

quoted

+address for the client whose addresses keeps on changing e.g Current stack

                                                    changing, e.g., current stack

quoted

+address of task keep on changing on context switch for each core. So these

                    keeps

quoted

+clients can update their addresses with ``qcom_apss_minidump_update_region``
+API.
+
+The driver also supports registration for the clients who came before
+minidump driver was initialized. It maintains pending list of clients
+who came before minidump and once minidump is initialized it registers
+them in one go.
+
+To simplify post mortem debugging, driver creates and maintain an ELF

choose one:    postmortem or post-mortem

quoted

+header as first region that gets updated each time a new region gets
+registered.
+
+The solution supports extracting the ramdump/minidump produced either

                                         RAM dump/minidump

quoted

+over USB or stored to an attached storage device.
+
+Dependency of minidump kernel driver
+------------------------------------
+
+It is to note that whole of minidump thing depends on Qualcomm boot

s/thing //

quoted

+firmware whether it supports minidump or not. So, if the minidump
+smem id is present in shared memory, it indicates that minidump

    SMEM ID

quoted

+is supported from boot firmware and it is possible to dump linux

                                                               Linux

quoted

+(APSS) region as part of minidump collection.
+
+How a kernel client driver can register region with minidump
+------------------------------------------------------------
+
+Client driver can use ``qcom_apss_minidump_region_register`` API's to
+register and ``qcom_apss_minidump_region_unregister`` to unregister
+their region from minidump driver.
+
+Client need to fill their region by filling qcom_apss_minidump_region

           needs

quoted

+structure object which consist of the region name, region's

                           consists

quoted

+virtual and physical address and its size.
+
+Below is one sample client driver snippet which try to allocate

                                                    tries

quoted

+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 it with
+minidump.
+
+ .. code-block:: c
+
+  #include <soc/qcom/qcom_minidump.h>
+  [...]
+
+
+  [... inside a function ...]
+  struct qcom_apss_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);
+
+  [... Fill up the region object ...]
+  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;
+
+  ret = qcom_apss_minidump_region_register(&region);
+  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

                                                      DDR

quoted

+full dump) by writing appropriate value to Qualcomm's top control and
+status register(tcsr) in driver/firmware/qcom_scm.c .

           register (tcsr)

quoted

+
+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 "full,mini"

                 DDR

quoted

+will collect minidump along with fulldump.
+
+Writing to sysfs node 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

                          starting

quoted

+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

                                                      needs

quoted

+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

        needs

quoted

+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

           passed                  dexter.exe (Qualcomm tool)

quoted

+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

               USB, i.e.                   regions

quoted

+starts with md_*.
+
+Replacing the dexter.exe with some open source tool can be added as future
+scope of this document.

Thanks for the review, applied the change for the next version.

-- Mukesh