Re: [PATCH v4 01/21] docs: qcom: Add qualcomm minidump guide

Rob Herring
2023-06-28T23:21:41Z

On Wed, Jun 28, 2023 at 6:36 AM Mukesh Ojha <quic_mojha@quicinc.com> wrote:
>
> 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@quicinc.com>
> ---
> Documentation/admin-guide/index.rst | 1 +
> Documentation/admin-guide/qcom_minidump.rst | 293 ++++++++++++++++++++++++++++
> 2 files changed, 294 insertions(+)
> create mode 100644 Documentation/admin-guide/qcom_minidump.rst
>
> 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..a3a8cfee4555
> --- /dev/null
> +++ b/Documentation/admin-guide/qcom_minidump.rst
> @@ -0,0 +1,293 @@
> +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 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 contents
> + SS-ToC: Subsystem table of contents
> + SS0-SSn: Subsystem numbered from 0 to n
> +
> +It depends on targets how the underlying hardware taking care of the
> +implementation part for minidump like above diagram is for shared
> +memory and it is possible that this could be implemented via memory
> +mapped regions but the general idea remain same.
> +
> +In this document, SMEM will be used as the backend implementation of
> +minidump.
> +
> +SMEM as backend
> +----------------
> +
> +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.
> +
> +Minidump kernel driver concept
> +------------------------------
> +::
> +
> + Minidump Client-1 Client-2 Client-5 Client-n
> + | | | |
> + | | ... | ... |
> + | | | |
> + | | | |
> + | | | |
> + | | | |
> + | | | |
> + | | | |
> + | +---+--------------+----+ |
> + +-----------+ qcom_minidump(core) +--------+
> + | |
> + +------+-----+------+---+
> + | | |
> + | | |
> + +---------------+ | +--------------------+
> + | | |
> + | | |
> + | | |
> + v v v
> + +-------------------+ +-------------------+ +------------------+
> + |qcom_minidump_smem | |qcom_minidump_mmio | | qcom_minidump_rm |
> + | | | | | |
> + +-------------------+ +-------------------+ +------------------+
> + Shared memory Memory mapped IO Resource manager
> + (backend) (backend) (backend)
> +
> +
> +Kernel implementation of minidump driver is divided into two parts one is,
> +the core implementation called frontend driver ``qcom_minidump.c`` and this
> +is the driver will be exposing the API for clients and the other part is,
> +backend driver and its depends whether it is based on SMEM, MMIO or some
> +other way corressponding driver will be hooking itself up with the core
> +driver to get itself working. As of now, at a time one and only one backend
> +can be attached to the front-end either it is HOST or a guest VM.
> +
> +Qualcomm 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 gives a mechanism to update physical/virtual
> +address for the client whose addresses keeps on changing, e.g., current stack
> +address of task keeps on changing on context switch for each core. So these
> +clients can update their addresses with ``qcom_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
> +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
> +---------------
> +
> +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 starting with name ``md_*`` in PCAT configured directory
> +in x86_64 machine, so for above example from the client it will be

So I can't use my QCom laptop or M1 MacBook? This text won't age well,
so perhaps reword it.

Rob