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There is no local register interface to describe: frames >>>> arrive asynchronously into a reserved memory region written by the >>>> host's display engine over PCIe, and this node only identifies that >>>> region. >>>> >>>> memory-region accepts an optional second entry for a host-written >>>> control mailbox, letting the driver detect the mode the host is >>>> actually driving instead of only echoing back the configured capture >>>> format. >>>> >>>> Signed-off-by: Tzu-Hao Wei >>>> --- >>>> .../bindings/media/axiado,ax3000-video.yaml | 44 ++++++++++++++++++++++ >>>> MAINTAINERS | 8 ++++ >>>> 2 files changed, 52 insertions(+) >>>> >>>> diff --git a/Documentation/devicetree/bindings/media/axiado,ax3000-video.yaml b/Documentation/devicetree/bindings/media/axiado,ax3000-video.yaml >>>> new file mode 100644 >>>> index 0000000000000000000000000000000000000000..c6d8d1843aac9f42869ff90a550b92d0bed7c16f >>>> --- /dev/null >>>> +++ b/Documentation/devicetree/bindings/media/axiado,ax3000-video.yaml >>>> @@ -0,0 +1,44 @@ >>>> +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause) >>>> +%YAML 1.2 >>>> +--- >>>> +$id: http://devicetree.org/schemas/media/axiado,ax3000-video.yaml# >>>> +$schema: http://devicetree.org/meta-schemas/core.yaml# >>>> + >>>> +title: Axiado AX3000 Video Controller >>>> + >>>> +maintainers: >>>> + - Shubhangini G >>>> + - Tzu-Hao Wei >>>> + - Prasad Bolisetty >>>> + >>>> +description: >>>> + Axiado AX3000 video capture controller. Reads frames written by the >>>> + display engine into a shared reserved memory region and exposes them >>>> + as a V4L2 capture device. >>> >>> This is really incomplete. You need at least way to power things on, >>> reset them, provide clocks, sensors, data paths. Or at the very minimal: >>> START capturing the frames after configuring the resolution. >>> >>> It seems you described driver or just a piece of entire video pipeline. >>> >> >> Thanks for your feedback. >> >> The Axiado AX3000 and AX3005 SoCs expose a display capture path that >> delivers frames into a shared reserved memory region and exposes them >> as a standard V4L2 capture device via the videobuf2 framework. >> >> There is no local register interface for this driver to program: frame >> delivery is controlled entirely by the host-side display engine and >> the PCIe endpoint mapping that feeds the shared region, both external >> to this driver. A software polling timer schedules a workqueue item at >> the configured framerate, which copies frames from the WC-mapped >> shared region into vmalloc-backed vb2 buffers. Running the copy in a >> work item rather than directly in the timer callback keeps potentially >> multi-megabyte memcpy and per-pixel conversion work out of softirq >> context. > > Then this is not a separate device. You just described a Linux driver. > > I still wait for answers of my question above. You described getting > buffers only. > Thank you for the continued review. To correctly represent this in device tree without describing a software driver as a hardware device, would moving the schema into /reserved-memory be the preferred approach for v2? Specifically, we are considering moving it to: Documentation/devicetree/bindings/reserved-memory/axiado,ax3000-video-mem.yaml This would follow the same Devicetree architectural pattern as qcom,rmtfs-mem: Documentation/devicetree/bindings/reserved-memory/qcom,rmtfs-mem.yaml Just as qcom,rmtfs-mem describes a reserved memory buffer used by remote processors and exports /dev/rmtfs_mem%d without hardware MMIO registers, clocks, or resets, axiado,ax3000-video describes the reserved memory buffer used by the AX3000 display pipeline and exports /dev/video0. Does representing axiado,ax3000-video as a reserved-memory node look like the appropriate way to model this in v2? Best regards, TH >> >> To provide more context, this hardware path is designed for BMC iKVM >> applications. The physical data flow is: >> Host Display Engine -> PCIe -> BMC Shared Memory -> v4l2 (video0). > > Great, not a device. Linux driver. > >> >>>> + >>>> +properties: >>>> + compatible: >>>> + oneOf: >>>> + - const: axiado,ax3000-video >>>> + - items: >>>> + - const: axiado,ax3005-video >>>> + - const: axiado,ax3000-video >>>> + >>>> + memory-region: >>>> + minItems: 1 >>>> + items: >>>> + - description: video frame buffer, shared with the display engine >>>> + - description: optional control mailbox, shared with the host >>> >>> Why is it optional? >>> >> >> The second memory region is optional because it is not available on all >> supported hardware configurations or use cases. >> >> For instance, another supported use case has the following data flow: >> vtconsole -> framebuffer -> Shared Memory -> v4l2 (video0). > > Use case is irrelevant to actual hardware. > > > Best regards, > Krzysztof