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56 lines
2.3 KiB
Text
56 lines
2.3 KiB
Text
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/** \page page_dma_buf DMA-BUF sharing
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PipeWire supports sharing Direct Memory Access buffers (DMA-BUFs) between
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clients via the `SPA_DATA_DmaBuf` data type. However properly negociating
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DMA-BUF support on both the producer and the consumer side require following
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a specific procedure. This page describes said procedure.
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# Stream parameters
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The stream parameters should contain two `SPA_PARAM_EnumFormat` objects: the
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first one is used for DMA-BUFs, the second one for shared memory buffers as a
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fallback.
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Query the list of all supported modifiers from your graphics API of choice.
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Add a `SPA_FORMAT_VIDEO_modifier` property to the first stream parameter with
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the flags `SPA_POD_PROP_FLAG_MANDATORY | SPA_POD_PROP_FLAG_DONT_FIXATE`. The
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value of the property should be set to a `SPA_CHOICE_Enum` containing once
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`long` choice per supported modifier, plus `DRM_FORMAT_MOD_INVALID` if the
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graphics API supports modifier-less buffers.
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The second stream parameter should not contain any `SPA_FORMAT_VIDEO_modifier`
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property.
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# `param_changed` hook for `SPA_PARAM_Format`
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Use `spa_pod_find_prop(param, NULL, SPA_FORMAT_VIDEO_modifier)` to check
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whether modifiers were negotiated. If they were negotiated, set the
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`SPA_PARAM_BUFFERS_dataType` property to `1 << SPA_DATA_DmaBuf`. If they were
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not negotiated, fall back to shared memory.
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## For producers
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When allocating a buffer, collect all possible modifiers from the
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`SPA_FORMAT_VIDEO_modifier` property and pass them all to the graphics API.
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If the allocation fails and the list of possible modifiers contains
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`DRM_FORMAT_MOD_INVALID`, fall back to allocating without an explicit modifier
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if the graphics API allows it.
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Once a buffer has been allocated, update the `SPA_PARAM_Format` parameter of
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the stream. Set the `SPA_FORMAT_VIDEO_modifier` property to the modifier of the
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buffer as `long`. Set the `SPA_PARAM_BUFFERS_stride` to the stride of the
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buffer.
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## For consumers
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Use `spa_format_video_raw_parse` to get the final stride and modifier.
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# For consumers: `add_buffer` hook
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Get the DMA-BUF FD and import it to the graphics API. If the modifier is not
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`DRM_FORMAT_MOD_INVALID`, provide the modifier to the graphics API. If the
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modifier is `DRM_FORMAT_MOD_INVALID`, import the DMA-BUF without an explicit
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modifier if the graphics API allows it.
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*/
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