BUD17-214: Bus scaling QoS update
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The document outlines the challenges and solutions related to on-chip interconnect buses in System on Chip (SoC) architectures, emphasizing the need for a common framework in the upstream Linux kernel. It proposes a new interconnect framework with vendor-specific drivers and a consumer API for managing data flow and resource allocation effectively. Future work includes incorporating feedback for enhancements, exploring additional Quality of Service (QoS) constraints, and extending support for specific interconnect drivers.
BUD17-214: Bus scaling QoS update
- 1. Bus scaling QoS update Georgi Djakov
- 2. ENGINEERS AND DEVICES WORKING TOGETHER Agenda ● Background ● The problem ● The solution ● Next steps
- 3. ENGINEERS AND DEVICES WORKING TOGETHER Background ● Challenges of SoC architecture ○ More and more features (IP cores) ○ Many components talking to each other ○ Multiple sources of traffic ○ Concurrent transfers ○ Predictability ● Evolution of on-chip interconnects ○ Buses, crossbars, network-on-chip ● Benefits ○ Scalability - packet communication ○ Power efficiency - shorter wires
- 4. ENGINEERS AND DEVICES WORKING TOGETHER An example NoC topology
- 5. ENGINEERS AND DEVICES WORKING TOGETHER The problem ● On-chip interconnect buses can handle high throughput data transfers, but most of the time they may be idle. ● Simultaneous data flows across the SoC with different sources and destinations, interleaved traffic. ● Interconnect buses can be configured according to the use-case and demand. ● Each SoC vendor has its own custom implementation in the downstream kernel. ● Need a common solution in the upstream Linux kernel.
- 6. ENGINEERS AND DEVICES WORKING TOGETHER Requirements ● Description of the topology. ● Expose path between endpoints as resources. The path is claimed by consumer drivers and they set constraints on it. ● A common framework for that can traverse the topology and allow a consumer driver to get() a path. ● Track and aggregate requests received from drivers. ● Update constraints and set hardware to most optimal configuration. ● The vendor specific interconnect controller drivers register the topology with the framework and implements low-level operations.
- 7. ENGINEERS AND DEVICES WORKING TOGETHER The solution ● A new framework - interconnect framework ● Vendor specific low-level drivers that control the hardware ● Consumer API to set constraints from drivers
- 8. ENGINEERS AND DEVICES WORKING TOGETHER Device-Tree binding ● Interconnect provider snoc: snoc@0580000 { compatible = "qcom,msm-bus-snoc"; #interconnect-cells = <1>; interconnect-port = <&bimc MAS_SNOC_CFG>, <&bimc SNOC_BIMC_0_MAS>, <&bimc SNOC_BIMC_1_MAS>, <&pnoc SNOC_PNOC_SLV>;
- 9. ENGINEERS AND DEVICES WORKING TOGETHER Device-Tree binding ● Interconnect consumer sdhc_1: sdhci@07824000 { … interconnect-port = <&pnoc MAS_PNOC_SDCC_1>; interconnect-path = <&mem>, <&usb_otg>; interconnect-path-names = "mem", "usb";
- 10. ENGINEERS AND DEVICES WORKING TOGETHER Interconnect API ● struct interconnect_path *interconnect_get(struct device *dev, const char *id); ● int interconnect_set(struct interconnect_path *path, u32 bandwidth); ● void interconnect_put(struct interconnect_path *path);
- 11. ENGINEERS AND DEVICES WORKING TOGETHER Interconnect API ● Currently works only with device-tree and platform drivers ● Use device-tree to denote path endpoints ● Types of constraints ● PM QoS
- 12. ENGINEERS AND DEVICES WORKING TOGETHER The first vendor specific driver ● Dragonboard 410c as a test platform. ● Test scenarios ○ Data transfers between peripherals ○ Data transfers from/to memory
- 13. ENGINEERS AND DEVICES WORKING TOGETHER Future work ● Feedback ○ LKML ○ Should we use PM QoS? ○ Remove dependency on DT ○ Support for ACPI? ○ Use integers instead of string ids for the binding ● Add support for other types of QoS constraints ○ Average bandwidth ○ Peak bandwidth ○ Round-trip latency ○ Priority ● Extend the Qualcomm msm8916 interconnect driver ○ Include the full topology ● Practical and easy example for testing
- 14. Thank You #BUD17 For further information: www.linaro.org BUD17 keynotes and videos on: connect.linaro.org