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[Why] Brightness programming may involve a conversion of a user requested brightness against what was in a custom brightness curve. The values might not match what a user programmed. [How] Add a new trace event to show specific converted brightness values. Reviewed-by: Alex Hung <alex.hung@amd.com> Link: https://lore.kernel.org/r/20250623171114.1156451-2-mario.limonciello@amd.com Signed-off-by: Mario Limonciello <mario.limonciello@amd.com> Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
105 lines
3.7 KiB
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105 lines
3.7 KiB
ReStructuredText
===============
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GPU Debugging
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===============
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General Debugging Options
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=========================
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The DebugFS section provides documentation on a number files to aid in debugging
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issues on the GPU.
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GPUVM Debugging
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===============
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To aid in debugging GPU virtual memory related problems, the driver supports a
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number of options module parameters:
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`vm_fault_stop` - If non-0, halt the GPU memory controller on a GPU page fault.
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`vm_update_mode` - If non-0, use the CPU to update GPU page tables rather than
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the GPU.
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Decoding a GPUVM Page Fault
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===========================
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If you see a GPU page fault in the kernel log, you can decode it to figure
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out what is going wrong in your application. A page fault in your kernel
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log may look something like this:
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::
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[gfxhub0] no-retry page fault (src_id:0 ring:24 vmid:3 pasid:32777, for process glxinfo pid 2424 thread glxinfo:cs0 pid 2425)
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in page starting at address 0x0000800102800000 from IH client 0x1b (UTCL2)
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VM_L2_PROTECTION_FAULT_STATUS:0x00301030
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Faulty UTCL2 client ID: TCP (0x8)
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MORE_FAULTS: 0x0
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WALKER_ERROR: 0x0
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PERMISSION_FAULTS: 0x3
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MAPPING_ERROR: 0x0
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RW: 0x0
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First you have the memory hub, gfxhub and mmhub. gfxhub is the memory
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hub used for graphics, compute, and sdma on some chips. mmhub is the
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memory hub used for multi-media and sdma on some chips.
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Next you have the vmid and pasid. If the vmid is 0, this fault was likely
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caused by the kernel driver or firmware. If the vmid is non-0, it is generally
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a fault in a user application. The pasid is used to link a vmid to a system
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process id. If the process is active when the fault happens, the process
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information will be printed.
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The GPU virtual address that caused the fault comes next.
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The client ID indicates the GPU block that caused the fault.
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Some common client IDs:
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- CB/DB: The color/depth backend of the graphics pipe
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- CPF: Command Processor Frontend
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- CPC: Command Processor Compute
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- CPG: Command Processor Graphics
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- TCP/SQC/SQG: Shaders
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- SDMA: SDMA engines
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- VCN: Video encode/decode engines
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- JPEG: JPEG engines
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PERMISSION_FAULTS describe what faults were encountered:
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- bit 0: the PTE was not valid
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- bit 1: the PTE read bit was not set
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- bit 2: the PTE write bit was not set
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- bit 3: the PTE execute bit was not set
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Finally, RW, indicates whether the access was a read (0) or a write (1).
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In the example above, a shader (cliend id = TCP) generated a read (RW = 0x0) to
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an invalid page (PERMISSION_FAULTS = 0x3) at GPU virtual address
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0x0000800102800000. The user can then inspect their shader code and resource
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descriptor state to determine what caused the GPU page fault.
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UMR
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===
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`umr <https://gitlab.freedesktop.org/tomstdenis/umr>`_ is a general purpose
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GPU debugging and diagnostics tool. Please see the umr
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`documentation <https://umr.readthedocs.io/en/main/>`_ for more information
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about its capabilities.
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Debugging backlight brightness
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==============================
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Default backlight brightness is intended to be set via the policy advertised
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by the firmware. Firmware will often provide different defaults for AC or DC.
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Furthermore, some userspace software will save backlight brightness during
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the previous boot and attempt to restore it.
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Some firmware also has support for a feature called "Custom Backlight Curves"
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where an input value for brightness is mapped along a linearly interpolated
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curve of brightness values that better match display characteristics.
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In the event of problems happening with backlight, there is a trace event
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that can be enabled at bootup to log every brightness change request.
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This can help isolate where the problem is. To enable the trace event add
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the following to the kernel command line:
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tp_printk trace_event=amdgpu_dm:amdgpu_dm_brightness:mod:amdgpu trace_buf_size=1M
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