Project Name: Qualcomm Weston SDM Backend
Core Purpose: Routing standard Upstream Weston calls into Qualcomm's downstream open-source Snapdragon Display Manager (SDM), which in turn manages all interactions with the standard Linux DRM/KMS display driver.
The software acts purely as a routing bridge. It does not perform any hardware-level scheduling, composition planning, or device programming itself. Instead, it coordinates calls across the following standard pipeline:
[ Upstream Weston Compositor ]
|
| (1. Sends standard frame repaint, layout, & buffer updates)
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=== THIS CODEBASE: WESTON SDM BACKEND (sdm-backend.so Router) ===
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| (2. Packages and routes these standard calls directly into SDM)
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[ Qualcomm Downstream Open-Source SDM Client/Libraries ]
|
| (3. Determines composition strategies & manages SDE resources)
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[ Linux Kernel DRM / KMS Driver Stack ]
- Upstream Weston: Manages the window manager shell, tracks window hierarchies, schedules frame repaints, and generates client buffers.
- Weston SDM Backend (This Codebase): Serves as the standard routing layer. It captures standard Weston calls (like output repaints, display hotplugs, VBlanks, and configurations) and routes them straight into the abstract C++ interfaces of the downstream SDM client. It contains no composition strategy or hardware-direct orchestration of its own.
- Downstream SDM: Acts as the intelligent hardware and display controller manager. It evaluates display layouts, implements the actual composition strategies, schedules hardware display pipelines, and manages all interactions and programming with the Linux Kernel DRM/KMS driver.
This diagram outlines the internal division of labor between Upstream, Open Source, and Proprietary layers within the SDM stack:
- Wayland Client & Compositor (Weston): Upstream standard interfaces.
- SDM-Backend & SDM 2.0 Interface: Open-source translation layer routing Weston compositor calls to the downstream SDM client.
- SDM-Client & SDM Interfaces: Core management layer separating the open-source display/composition manager from proprietary strategies.
- Proprietary Plugins (Blue/Orange): Handle strategy implementations, resource management, partial updates, pipe allocation, rotators, scalars, QoS, and tone-mapping.
- Downstream DRM Driver & DPU: Target hardware-specific execution layer.
| SDM 1.0 API | SDM 2.0 API |
|---|---|
CoreInterface::CreateDisplay() |
SDMDisplayLifeCycleIntf::CreateDisplay() |
DisplayInterface::Prepare() |
SDMDisplayDrawCycleIntf::CommitOrPrepare() |
DisplayInterface::Commit() |
SDMDisplayDrawCycleIntf::PresentDisplay() |
DisplayInterface::SetDisplayState() |
SDMDisplayLifeCycleIntf::SetDisplayState() |
DisplayInterface::SetVSyncState() |
SDMDisplayDrawCycleIntf::SetVsyncEnabled() |
DisplayInterface::GetDisplayAttributes() |
SDMDisplayCapsIntf::GetDisplayConfig() |
DisplayInterface::SetPanelBrightness() |
SDMDisplaySettingsIntf::SetPanelBrightness() |
DisplayInterface::GetPanelBrightness() |
SDMDisplaySettingsIntf::GetPanelBrightness() |
DisplayInterface::MinHdcpEncryptionLevelChanged() |
SDMDisplayDrawCycleIntf::MinHdcpEncryptionLevelChanged() |
| SDM 1.0 API | SDM 2.0 API |
|---|---|
LayerStack structure with Layer* pointers |
std::vector<int64_t> layer_ids_ |
Manual Layer object allocation |
SDMDisplayLayerBuilderIntf::CreateLayer() |
Manual Layer object deallocation |
SDMDisplayLayerBuilderIntf::DestroyLayer() |
Direct Layer field assignment |
SDMDisplayLayerBuilderIntf::SetLayerBuffer(), SetLayerSourceCrop(), SetLayerDisplayFrame(), SetLayerVisibleRegion(), SetLayerSurfaceDamage(), SetLayerTransform(), SetLayerBlendMode(), SetLayerPlaneAlpha(), SetLayerType(), SetLayerFlag(), SetLayerCompositionType() |
layer->composition field access |
SDMDisplayLayerBuilderIntf::GetDeviceSelectedCompositionType() |
layer->input_buffer.color_metadata field access |
SDMDisplayLayerBuilderIntf::GetLayerColorMetadata() |
layer->input_buffer.release_fence_fd field access |
SDMDisplayDrawCycleIntf::GetReleaseFences() |
layer_stack_.retire_fence field |
retire_fence_ member variable |
layer_stack_.flags.hdr_present field |
hdr_present_ member variable |
| SDM 1.0 | SDM 2.0 |
|---|---|
CoreInterface* (single interface) |
SDMDisplayLifeCycleIntf*, SDMDisplayDrawCycleIntf*, SDMDisplayLayerBuilderIntf*, SDMDisplayCapsIntf*, SDMDisplaySettingsIntf*, SDMDisplaySideBandIntf*, SDMDisplayAiqeIntf* |
DisplayInterface* (single interface) |
Split into 7 specialized SDM 2.0 interfaces above |
- backend-sdm-2.0.1/README.md (Added)
- backend-sdm-2.0.1/meson.build (Modified - Added libsdmclient dependency)
- backend-sdm-2.0.1/sdm-service/sdm_color_mode_intf.h (Modified)
- backend-sdm-2.0.1/sdm-service/sdm_color_mode_intf_impl.h (Modified)
- backend-sdm-2.0.1/sdm-service/sdm_color_mode_intf_impl.cpp (Modified)
- backend-sdm-2.0.1/sdm-service/sdm_display.h (Modified)
- backend-sdm-2.0.1/sdm-service/sdm_display.cpp (Modified)
- backend-sdm-2.0.1/sdm-service/sdm_display_connect.h (Modified)
- backend-sdm-2.0.1/sdm-service/sdm_display_connect.cpp (Modified)
✅ Migration Complete - All SDM 1.0 APIs replaced with SDM 2.0 APIs
This project is licensed under the LICENSE.