Re: [Patch v6 03/12] docs: qcom: Add qualcomm minidump guide

[Bagas Sanjaya]

On Sat, Nov 25, 2023 at 03:49:46AM +0530, Mukesh Ojha wrote:
> diff --git a/Documentation/admin-guide/index.rst b/Documentation/admin-guide/index.rst
> index 43ea35613dfc..251d070486c2 100644
> --- a/Documentation/admin-guide/index.rst
> +++ b/Documentation/admin-guide/index.rst
> @@ -120,6 +120,7 @@ configure specific aspects of kernel behavior to your liking.
>     perf-security
>     pm/index
>     pnp
> +   qcom_minidump
>     rapidio
>     ras
>     rtc
> diff --git a/Documentation/admin-guide/qcom_minidump.rst b/Documentation/admin-guide/qcom_minidump.rst
> new file mode 100644
> index 000000000000..b492f2b79639
> --- /dev/null
> +++ b/Documentation/admin-guide/qcom_minidump.rst
> @@ -0,0 +1,272 @@
> +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 RAM dumps 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 selected 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 contents
> +       SS-ToC: Subsystem table of contents
> +       SS0-SSn: Subsystem numbered from 0 to n
> +
> +It depends on SoC where the underlying firmware is keeping the
> +minidump global table taking care of subsystem ToC part for
> +minidump like for above diagram, it is for shared memory sitting
> +in DDR and it is shared among various master however it is possible
> +that this could be implemented via memory mapped regions but the
> +general idea should remain same. Here, various subsystem could be
> +DSP's like ADSP/CDSP/MODEM etc, along with Application processor
> +(APSS) where Linux runs. DSP minidump gets collected when DSP's goes
> +for recovery followed by a crash. The minidump part of code for
> +that resides in ``qcom_rproc_minidump.c``.
> +
> +
> +SMEM as backend
> +----------------
> +
> +In this document, SMEM will be used as the backend implementation
> +of minidump.
> +
> +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 contents (G-ToC). Each subsystem (APSS, ADSP, ...) has
> +its 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 its size etc. and it
> +could be anywhere scattered in the DDR.
> +
> +Qualcomm APSS Minidump kernel driver concept
> +--------------------------------------------
> +
> +Qualcomm APSS minidump kernel driver adds the capability to add Linux
> +region to be dumped as part of RAM dump collection. At the moment,
> +shared memory driver creates platform device for minidump driver and
> +give a means to APSS minidump to initialize itself on probe.
> +
> +This driver provides ``qcom_minidump_region_register`` and
> +``qcom_minidump_region_unregister`` API's to register and unregister
> +APSS minidump region. It 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
> +header as first region that gets updated each time a new region gets
> +registered.
> +
> +The solution supports extracting the RAM dump/minidump produced either
> +over USB or stored to an attached storage device.
> +
> +Dependency of minidump kernel driver
> +------------------------------------
> +
> +It is to note that whole of minidump depends on Qualcomm boot firmware
> +whether it supports minidump or not. So, if the minidump SMEM ID is
> +present in shared memory, it indicates that minidump is supported from
> +boot firmware and it is possible to dump Linux (APSS) region as part
> +of minidump collection.
> +
> +How a kernel client driver can register region with minidump
> +------------------------------------------------------------
> +
> +Client driver can use ``qcom_minidump_region_register`` API's to register
> +and ``qcom_minidump_region_unregister`` to unregister their region from
> +minidump driver.
> +
> +Client needs to fill their region by filling ``qcom_minidump_region``
> +structure object which consists of the region name, region's virtual
> +and physical address and its size.
> +
> +Below, is one sample client driver snippet which tries 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 it with minidump.
> +
> + .. code-block:: c
> +
> +  #include <soc/qcom/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);
> +
> +  [... 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_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 RAM dump (also called
> +full dump) by 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 RAM dump will be collected while setting it ``"full,mini"``
> +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
> +---------------
> +::
> +
> +	+-----------+
> +	|           |
> +	|           |         +------+
> +	|           |         |      |
> +	|           |         +--+---+ Product(Qualcomm SoC)
> +	+-----------+             |
> +	|+++++++++++|<------------+
> +	|+++++++++++|    usb cable
> +	+-----------+
> +            x86_64 PC
> +
> +The solution supports a product running with Qualcomm SoC (where minidump)
> +is supported from the firmware) connected to x86_64 host PC running PCAT
> +tool. It supports downloading the minidump produced from product to the
> +host PC over USB or to save the minidump to the product attached storage
> +device(UFS/eMMC/SD Card) into minidump dedicated partition.
> +
> +By default, dumps are downloaded via USB to the attached x86_64 PC running
> +PCAT (Qualcomm tool) software. Upon download, we will see a set of binary
> +blobs starting 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 needs to write appropriate
> +value to IMEM register, in that case dumps are collected in rawdump
> +partition on the product device itself.
> +
> +One needs 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 passed 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 regions as blobs
> +and their name starts with ``md_*``.
> +
> +Replacing the ``dexter.exe`` with some open source tool can be added as future
> +scope of this document.

LGTM, thanks!

Reviewed-by: Bagas Sanjaya <bagasdotme@xxxxxxxxx>

-- 
An old man doll... just what I always wanted! - Clara

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