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authorKees Cook <kees+treewide@kernel.org>2026-09-02 15:31:14 -0700
committerKees Cook <kees@kernel.org>2026-09-04 21:37:00 -0700
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treec65086f9bdcd48c6360fb7cb4598bca084da1f32 /Documentation/admin-guide/media/vimc.rst
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treewide: refresh kmalloc_obj() conversionsgrafted
This is another run of the Coccinelle script for converting kmalloc() family of allocations to kmalloc_obj() via the existing rules in scripts/coccinelle/api/kmalloc_objs.cocci This catches both the set of kmalloc() uses added since the first kmalloc_obj() conversions in v7.0 and adds a large group missed in the first pass due to Coccinelle not interacting well with the cleanup.h scoped_...() family of macros[1]. I worked around this with spatch's "--macro-file" argument to a file with all the scoped_...() macros mapped to Coccinelle's YACFE_ITERATOR[2] as that was the closest viable control flow indicator I could find. Build tested allmodconfig on x86, arm64, arm, loongarch, mips, powerpc, riscv, and s390 with no new warnings. Link: https://lore.kernel.org/lkml/202609021314.8A9C0B8@keescook/ [1] Link: https://github.com/coccinelle/coccinelle/blob/master/standard.h [2] Signed-off-by: Kees Cook <kees+treewide@kernel.org>
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+.. SPDX-License-Identifier: GPL-2.0
+
+The Virtual Media Controller Driver (vimc)
+==========================================
+
+The vimc driver emulates complex video hardware using the V4L2 API and the Media
+API. It has a capture device and three subdevices: sensor, debayer and scaler.
+
+Topology
+--------
+
+The topology is hardcoded, although you could modify it in vimc-core and
+recompile the driver to achieve your own topology. This is the default topology:
+
+.. _vimc_topology_graph:
+
+.. kernel-figure:: vimc.dot
+ :alt: Diagram of the default media pipeline topology
+ :align: center
+
+ Media pipeline graph on vimc
+
+Configuring the topology
+~~~~~~~~~~~~~~~~~~~~~~~~
+
+Each subdevice will come with its default configuration (pixelformat, height,
+width, ...). One needs to configure the topology in order to match the
+configuration on each linked subdevice to stream frames through the pipeline.
+If the configuration doesn't match, the stream will fail. The ``v4l-utils``
+package is a bundle of user-space applications, that comes with ``media-ctl`` and
+``v4l2-ctl`` that can be used to configure the vimc configuration. This sequence
+of commands fits for the default topology:
+
+.. code-block:: bash
+
+ media-ctl -d platform:vimc -V '"Sensor A":0[fmt:SBGGR8_1X8/640x480]'
+ media-ctl -d platform:vimc -V '"Debayer A":0[fmt:SBGGR8_1X8/640x480]'
+ media-ctl -d platform:vimc -V '"Scaler":0[fmt:RGB888_1X24/640x480]'
+ media-ctl -d platform:vimc -V '"Scaler":0[crop:(100,50)/400x150]'
+ media-ctl -d platform:vimc -V '"Scaler":1[fmt:RGB888_1X24/300x700]'
+ v4l2-ctl -z platform:vimc -d "RGB/YUV Capture" -v width=300,height=700
+ v4l2-ctl -z platform:vimc -d "Raw Capture 0" -v pixelformat=BA81
+
+Subdevices
+----------
+
+Subdevices define the behavior of an entity in the topology. Depending on the
+subdevice, the entity can have multiple pads of type source or sink.
+
+vimc-sensor:
+ Generates images in several formats using video test pattern generator.
+ Exposes:
+
+ * 1 Pad source
+
+vimc-lens:
+ Ancillary lens for a sensor. Supports auto focus control. Linked to
+ a vimc-sensor using an ancillary link. The lens supports FOCUS_ABSOLUTE
+ control.
+
+.. code-block:: bash
+
+ media-ctl -p
+ ...
+ - entity 28: Lens A (0 pad, 0 link)
+ type V4L2 subdev subtype Lens flags 0
+ device node name /dev/v4l-subdev6
+ - entity 29: Lens B (0 pad, 0 link)
+ type V4L2 subdev subtype Lens flags 0
+ device node name /dev/v4l-subdev7
+ v4l2-ctl -d /dev/v4l-subdev7 -C focus_absolute
+ focus_absolute: 0
+
+
+vimc-debayer:
+ Transforms images in bayer format into a non-bayer format.
+ Exposes:
+
+ * 1 Pad sink
+ * 1 Pad source
+
+vimc-scaler:
+ Re-size the image to meet the source pad resolution. E.g.: if the sync
+ pad is configured to 360x480 and the source to 1280x720, the image will
+ be stretched to fit the source resolution. Works for any resolution
+ within the vimc limitations (even shrinking the image if necessary).
+ Exposes:
+
+ * 1 Pad sink
+ * 1 Pad source
+
+vimc-capture:
+ Exposes node /dev/videoX to allow userspace to capture the stream.
+ Exposes:
+
+ * 1 Pad sink
+ * 1 Pad source
+
+Module options
+--------------
+
+Vimc has a module parameter to configure the driver.
+
+* ``allocator=<unsigned int>``
+
+ memory allocator selection, default is 0. It specifies the way buffers
+ will be allocated.
+
+ - 0: vmalloc
+ - 1: dma-contig