memory_size

Source code: memory_size.py

Test if the memory size is correctly written in the firmware.

Description

Linux kernel trusts the available memory region specified from firmware, via ACPI or Device Tree. However, it is possible for the firmware to send wrong values, for example always only assigning 8GB for kernel while the system has 16GB memory installed.

On traditional PC, the memory information is stored on SPD chipset on memory module so firmware should read and claim free space for kernel according to SPD. On modern Chromebooks, the SPD is replaced by a pre-defined mapping table and decided by straps. When the mapping table is out-dated, for example if an old firmware is installed, then the allocated memory for kernel would be wrong.

The Chrome OS command, mosys, can read from physical or virtual SPD and report expected memory size. So this test tries to compare the value from mosys and kernel meminfo to figure out if firmware has reported wrong memory size for kernel.

Usually firmware has to reserve some memory, for example ACPI tables, DMA, I/O port mappings, so the kernel is expected to get less memory. This is specified by argument max_diff_ratio.

Meanwhile, for virtual SPD, it is possible that both firmware and mosys have out-dated information of memory straps, so optionally we support a third source, the shopfloor backend, to provide memory size.

If argument device_data_key is set, we will also check memory size by the information from device data (usually retrieved from shopfloor backend if factory supports it).

Test Procedure

This is an automated test without user interaction.

When started, the test collects memory size information from different source and fail if the difference is too large.

Dependency

• Command mosys: mosys -k memory spd print geometry.

• Kernel to support /proc/meminfo, search for string MemTotal.

• Optionally, shopfloor integration to save memory in device data.

Examples

To compare and check the memory size from mosys and kernel:

{
  "pytest_name": "memory_size",
  "label": "Memory Size",
  "related_components": [
    "test_tags.TestCategory.DRAM"
  ]
}

To compare and check the memory size from mosys and kernel, with difference up to 5 percent:

{
  "pytest_name": "memory_size",
  "label": "Memory Size Max Diff Ratio 5 Percent",
  "related_components": [
    "test_tags.TestCategory.DRAM"
  ],
  "args": {
    "max_diff_ratio": 0.05
  }
}

To compare and check the memory size from mosys, kernel, and device data component.memory_size:

{
  "label": "Memory Size Compare To Device Data",
  "subtests": [
    {
      "pytest_name": "scan",
      "label": "Scan Memory Size in GB",
      "related_components": [
        "test_tags.TestCategory.VPD"
      ],
      "action_on_failure": "STOP",
      "args": {
        "device_data_key": "component.memory_size",
        "label": "Memory Size in GB"
      }
    },
    {
      "pytest_name": "memory_size",
      "label": "Memory Size",
      "related_components": [
        "test_tags.TestCategory.DRAM"
      ],
      "action_on_failure": "STOP",
      "args": {
        "device_data_key": "component.memory_size"
      }
    }
  ]
}

Test Arguments

Name	Type	Description
device_data_key	str, None	(optional; default: None) Device data key for getting memory size in GB.
max_diff_ratio	float	(optional; default: 0.2) Maximum tolerance difference between memory size detected by kernel and mosys within a ratio.