This patchset introduces the usage of configfs in order to create vimc devices
with a configured topology. A patch introducing configfs usage was already sent 
by Helen Koike: . The current patch is based on her 
patch but
suggests a new API for using configfs.
It uses symlinks to represent a link between two entities, an approach already 
used in the kernel
by usb gadgets composed with configfs to associate usb gadget's functions to 
its configurations.
For example, a topology of sensor->capture will be created with the following 


mkdir ${CONFIGFS_ROOT}/vimc/mdev/
mkdir ${CONFIGFS_ROOT}/vimc/mdev/vimc-sensor:sen
mkdir ${CONFIGFS_ROOT}/vimc/mdev/vimc-capture:cap
`-- vimc
    `-- mdev
        |-- hotplug
        |-- vimc-capture:cap
        |   `-- pad:sink:0
        `-- vimc-sensor:sen
            `-- pad:source:0

mkdir ${CONFIGFS_ROOT}/vimc/mdev/vimc-sensor:sen/pad:source:0/to-cap
ln -s ${CONFIGFS_ROOT}/vimc/mdev/vimc-capture:cap/pad:sink:0 
`-- vimc
    `-- mdev
        |-- hotplug
        |-- vimc-capture:cap
        |   `-- pad:sink:0
        `-- vimc-sensor:sen
            `-- pad:source:0
                `-- to-cap
                    |-- enabled
                    |-- immutable
                    `-- pad:sink:0 -> 

There are several reasons to prefer the symlink approach in order to represent 
links between entities.
The previous approach in which links are represented with directories of the 
form 'entity1:pad>-><entity2:pad'
requires userspace to parse the dirctories names in order to understand the 
topology, while in the symlink
approach userspace needs only to traverse the configfs tree.
Also, the usage of symlinks prevents userspace from creating links between 
entities that don't exist and also
an entity can't be removed if there is a symlink pointing to it or from it, 
while in the previous approach the
links were created by creating unrelated directories and care had to be taken 
to ensure consistency. This way
the topology configured from userspace is restricted to always be valid and 
represent the current topology of
the device. This results in less validation needed in kernel code when plugging 
the device and less possibility
for mistakes in the userspace side. Last, but not least, using symlinks is the 
natural way of associating things
in configfs.

This patch is meant to demonstrate the suggested configfs api and get comments 
and acceptance/disagreement from
the community. It passes few tests that configure basic topology and streams 
the capture entities.
Here is the tests script:
Further versions will go through more extensive debugging.

The patchset is rebased on top of v5 of the patchset 'Collapse vimc into single 
monolithic driver' sent by Shuah Khan

Patch 1, was sent by me before as a single patch and is needed for the configfs 

Patch 2, documents how to use the new configfs api in order to create and set 
devices topologies.

Patch 3, only adds the new configfs api code but does not use it yet, so it 
still creates only the hardcoded device.

Patch 4, removes the hardcoded device topology and creates devices with 
topologies configured with the configfs.

Patch 5, implements indexing for the bus_info field since now there can be more 
than one vimc device.

Dafna Hirschfeld (5):
  media: vimc: upon streaming, check that the pipeline starts with a
    source entity
  docs: media: vimc: Documenting vimc topology configuration using
  media: vimc: Add the implementation for the configfs api
  media: vimc: use configfs instead of having hardcoded configuration
  media: vimc: Add device index to the bus_info

 Documentation/media/v4l-drivers/    |  28 +-
 Documentation/media/v4l-drivers/vimc.rst    | 240 ++++++-
 drivers/media/platform/vimc/Kconfig         |   9 +-
 drivers/media/platform/vimc/Makefile        |   2 +-
 drivers/media/platform/vimc/vimc-capture.c  |  50 +-
 drivers/media/platform/vimc/vimc-common.h   |  86 ++-
 drivers/media/platform/vimc/vimc-configfs.c | 656 ++++++++++++++++++++
 drivers/media/platform/vimc/vimc-configfs.h |  41 ++
 drivers/media/platform/vimc/vimc-core.c     | 350 +++++------
 drivers/media/platform/vimc/vimc-debayer.c  |  35 +-
 drivers/media/platform/vimc/vimc-scaler.c   |  35 +-
 drivers/media/platform/vimc/vimc-sensor.c   |  33 +-
 drivers/media/platform/vimc/vimc-streamer.c |  39 +-
 13 files changed, 1289 insertions(+), 315 deletions(-)
 create mode 100644 drivers/media/platform/vimc/vimc-configfs.c
 create mode 100644 drivers/media/platform/vimc/vimc-configfs.h


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