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Documentation/gpu: Document how to narrow down display issues
The amdgpu driver is composed of multiple components, each of which can be a source of some specific problem that the user/developer can see. This commit introduces steps to narrow down and collect display information. Cc: Leo Li <sunpeng.li@amd.com> Cc: Aurabindo Pillai <aurabindo.pillai@amd.com> Cc: Hamza Mahfooz <hamza.mahfooz@amd.com> Cc: Harry Wentland <harry.wentland@amd.com> Cc: Mario Limonciello <mario.limonciello@amd.com> Cc: Christian Konig <christian.koenig@amd.com> Cc: Alex Deucher <alexander.deucher@amd.com> Signed-off-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com> Reviewed-by: Mario Limonciello <mario.limonciello@amd.com> Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
This commit is contained in:
Rodrigo Siqueira
Alex Deucher
parent
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dec36b22ca
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Display Core Debug tools
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========================
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In this section, you will find helpful information on debugging the amdgpu
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driver from the display perspective. This page introduces debug mechanisms and
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procedures to help you identify if some issues are related to display code.
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Narrow down display issues
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==========================
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Since the display is the driver's visual component, it is common to see users
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reporting issues as a display when another component causes the problem. This
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section equips users to determine if a specific issue was caused by the display
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component or another part of the driver.
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DC dmesg important messages
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---------------------------
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The dmesg log is the first source of information to be checked, and amdgpu
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takes advantage of this feature by logging some valuable information. When
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looking for the issues associated with amdgpu, remember that each component of
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the driver (e.g., smu, PSP, dm, etc.) is loaded one by one, and this
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information can be found in the dmesg log. In this sense, look for the part of
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the log that looks like the below log snippet::
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[ 4.254295] [drm] initializing kernel modesetting (IP DISCOVERY 0x1002:0x744C 0x1002:0x0E3B 0xC8).
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[ 4.254718] [drm] register mmio base: 0xFCB00000
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[ 4.254918] [drm] register mmio size: 1048576
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[ 4.260095] [drm] add ip block number 0 <soc21_common>
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[ 4.260318] [drm] add ip block number 1 <gmc_v11_0>
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[ 4.260510] [drm] add ip block number 2 <ih_v6_0>
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[ 4.260696] [drm] add ip block number 3 <psp>
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[ 4.260878] [drm] add ip block number 4 <smu>
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[ 4.261057] [drm] add ip block number 5 <dm>
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[ 4.261231] [drm] add ip block number 6 <gfx_v11_0>
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[ 4.261402] [drm] add ip block number 7 <sdma_v6_0>
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[ 4.261568] [drm] add ip block number 8 <vcn_v4_0>
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[ 4.261729] [drm] add ip block number 9 <jpeg_v4_0>
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[ 4.261887] [drm] add ip block number 10 <mes_v11_0>
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From the above example, you can see the line that reports that `<dm>`,
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(**Display Manager**), was loaded, which means that display can be part of the
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issue. If you do not see that line, something else might have failed before
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amdgpu loads the display component, indicating that we don't have a
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display issue.
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After you identified that the DM was loaded correctly, you can check for the
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display version of the hardware in use, which can be retrieved from the dmesg
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log with the command::
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dmesg | grep -i 'display core'
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This command shows a message that looks like this::
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[ 4.655828] [drm] Display Core v3.2.285 initialized on DCN 3.2
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This message has two key pieces of information:
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* **The DC version (e.g., v3.2.285)**: Display developers release a new DC version
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every week, and this information can be advantageous in a situation where a
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user/developer must find a good point versus a bad point based on a tested
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version of the display code. Remember from page :ref:`Display Core <amdgpu-display-core>`,
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that every week the new patches for display are heavily tested with IGT and
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manual tests.
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* **The DCN version (e.g., DCN 3.2)**: The DCN block is associated with the
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hardware generation, and the DCN version conveys the hardware generation that
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the driver is currently running. This information helps to narrow down the
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code debug area since each DCN version has its files in the DC folder per DCN
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component (from the example, the developer might want to focus on
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files/folders/functions/structs with the dcn32 label might be executed).
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However, keep in mind that DC reuses code across different DCN versions; for
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example, it is expected to have some callbacks set in one DCN that are the same
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as those from another DCN. In summary, use the DCN version just as a guide.
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From the dmesg file, it is also possible to get the ATOM bios code by using::
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dmesg | grep -i 'ATOM BIOS'
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Which generates an output that looks like this::
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[ 4.274534] amdgpu: ATOM BIOS: 113-D7020100-102
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This type of information is useful to be reported.
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Avoid loading display core
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--------------------------
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Sometimes, it might be hard to figure out which part of the driver is causing
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the issue; if you suspect that the display is not part of the problem and your
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bug scenario is simple (e.g., some desktop configuration) you can try to remove
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the display component from the equation. First, you need to identify `dm` ID
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from the dmesg log; for example, search for the following log::
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[ 4.254295] [drm] initializing kernel modesetting (IP DISCOVERY 0x1002:0x744C 0x1002:0x0E3B 0xC8).
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[..]
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[ 4.260095] [drm] add ip block number 0 <soc21_common>
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[ 4.260318] [drm] add ip block number 1 <gmc_v11_0>
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[..]
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[ 4.261057] [drm] add ip block number 5 <dm>
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Notice from the above example that the `dm` id is 5 for this specific hardware.
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Next, you need to run the following binary operation to identify the IP block
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mask::
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0xffffffff & ~(1 << [DM ID])
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From our example the IP mask is::
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0xffffffff & ~(1 << 5) = 0xffffffdf
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Finally, to disable DC, you just need to set the below parameter in your
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bootloader::
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amdgpu.ip_block_mask = 0xffffffdf
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If you can boot your system with the DC disabled and still see the issue, it
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means you can rule DC out of the equation. However, if the bug disappears, you
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still need to consider the DC part of the problem and keep narrowing down the
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issue. In some scenarios, disabling DC is impossible since it might be
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necessary to use the display component to reproduce the issue (e.g., play a
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game).
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**Note: This will probably lead to the absence of a display output.**
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Display flickering
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------------------
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Display flickering might have multiple causes; one is the lack of proper power
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to the GPU or problems in the DPM switches. A good first generic verification
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is to set the GPU to use high voltage::
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bash -c "echo high > /sys/class/drm/card0/device/power_dpm_force_performance_level"
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The above command sets the GPU/APU to use the maximum power allowed which
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disables DPM switches. If forcing DPM levels high does not fix the issue, it
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is less likely that the issue is related to power management. If the issue
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disappears, there is a good chance that other components might be involved, and
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the display should not be ignored since this could be a DPM issues. From the
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display side, if the power increase fixes the issue, it is worth debugging the
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clock configuration and the pipe split police used in the specific
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configuration.
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Display artifacts
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-----------------
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Users may see some screen artifacts that can be categorized into two different
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types: localized artifacts and general artifacts. The localized artifacts
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happen in some specific areas, such as around the UI window corners; if you see
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this type of issue, there is a considerable chance that you have a userspace
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problem, likely Mesa or similar. The general artifacts usually happen on the
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entire screen. They might be caused by a misconfiguration at the driver level
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of the display parameters, but the userspace might also cause this issue. One
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way to identify the source of the problem is to take a screenshot or make a
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desktop video capture when the problem happens; after checking the
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screenshot/video recording, if you don't see any of the artifacts, it means
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that the issue is likely on the the driver side. If you can still see the
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problem in the data collected, it is an issue that probably happened during
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rendering, and the display code just got the framebuffer already corrupted.
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Disabling/Enabling specific features
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====================================
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DC has a struct named `dc_debug_options`, which is statically initialized by
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all DCE/DCN components based on the specific hardware characteristic. This
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structure usually facilitates the bring-up phase since developers can start
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with many disabled features and enable them individually. This is also an
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important debug feature since users can change it when debugging specific
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issues.
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For example, dGPU users sometimes see a problem where a horizontal fillet of
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flickering happens in some specific part of the screen. This could be an
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indication of Sub-Viewport issues; after the users identified the target DCN,
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they can set the `force_disable_subvp` field to true in the statically
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initialized version of `dc_debug_options` to see if the issue gets fixed. Along
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the same lines, users/developers can also try to turn off `fams2_config` and
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`enable_single_display_2to1_odm_policy`. In summary, the `dc_debug_options` is
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an interesting form for identifying the problem.
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DC Visual Confirmation
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======================
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@ -76,6 +251,18 @@ change in real-time by using something like::
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When reporting a bug related to DC, consider attaching this log before and
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after you reproduce the bug.
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Collect Firmware information
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============================
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When reporting issues, it is important to have the firmware information since
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it can be helpful for debugging purposes. To get all the firmware information,
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use the command::
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cat /sys/kernel/debug/dri/0/amdgpu_firmware_info
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From the display perspective, pay attention to the firmware of the DMCU and
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DMCUB.
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DMUB Firmware Debug
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===================
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