Hi,
Continuing the discussion about the API of the vimc driver, I made some
changes
based on the previous comments, please see below and let me know your
opinion about it.
Helen
/***********************
Configfs considerations:
************************/
Informal definitions:
subsystem: the root driver folder in user space (/configfs/vimc)
item: aka a folder in user space
attributes: aka files in the folder
group: aka a folder that can contain subfolders (parent and child relation)
default group: aka a subfolder that is created automatically when the
"parent" folder is created
it is not considered a child in terms of rmdir
* Performing rmdir in a group will fail if it contain children that are
not default groups, i.e, if the
folder contain subfolders that are default group, then it can be removed
with rmdir, if the
subfolders were created with mkdir, then rmdir in the parent will fail.
* Configfs has the notion of committable item but it is not implemented
yet. A committable item is an item
that can be in one of two parent folders called: live and pending. The
idea is to create and modify the item
in the pending directory and then to move the item through a rename to
the live directory where
it can't be modified. This seems to be a nice feature for vimc, but as
it is not available yet the
proposal below won't be based on this.
* Groups can be dynamically created/destroyed by the driver whenever it
wants. Afaik attributes can only
be created when the group or item is created and symlinks can only be
create from user space, i.e, the
driver don't know how to create/destroy attributes or symlinks in anytime.
/***********************
The API:
************************/
In short, a topology like this one: http://goo.gl/Y7eUfu
Would look like this filesystem tree: https://goo.gl/mEOmOf
v3 core changes:
- I removed the use of symlinks as I wans't able to see how to do it nicely.
- I use the names of the folders created by user space to retrieve
information at mkdir time
- hotplug file in each entity
- hotplug file in each device
- reset file in each device
* The /configfs/vimc subsystem
empty when the driver is loaded
* Create a device
Userspace can create a new vimc device with:
$ mkdir /configfs/vimc/any_name
Example:
$ mkdir /configfs/vimc/vimc0
$ ls -l /configfs/vimc/vimc0
hotplug
reset
entities/
links/
entities/ and links/ folder are default groups, thus they don't prevent
rmdir vimc0/, but
rmdir will fail if it has any child inside entities/ or links/.
hotplug is used to plug and unplug the device, it can read "plugged" or
"unplugged" and user can
write "plug" or "unplug" to change its state.
Changing hotplug state will never fail as the configfs tree will always
be in a valid state.
reset is used to easily destroy all the topology without the need to
walk through all the children
to perform rmdir, writing 1 to reset file will set hotplug to
"unplugged" and erase all folders
under entities/ and links/.
* Create an entity
Userspace can create a new entity with:
$ mkdir /configfs/vimc/vimc0/entities/<role>:<name>
Example:
$ mkdir /configfs/vimc/vimc0/entities/sensor:SensorA
$ ls -l /configfs/vimc/vimc0/entities/sensor:SensorA
hotplug
pad:source:0/
The name of the folder needs to be in the format <role>:<name> or it
will be rejected, this allows the
creation of the right pads according to its role at mkdir time,
eliminating the previously proposed role
and name files.
hotplug is used to plug and unplug the hw block, it can read "plugged"
or "unplugged" and user can
write "plug" or "unplug" to change its state. As we don't support this
yet in the media core, changing it
will only be allowed if /configfs/vimc/vimc0/hotplug is "unplugged".
hotplug file is "unplugged" by default.
Pads will be created as default groups with the name in the format
pad:<direction>:<pad_number> and it
will be an empty folder.
If the hw block supports different number of pads, we could expose two
files:
sinks
sources
where the user space can write the desired number of sink and source
pads and the driver will dynamically
create the folders pad:<direction>:<pad_number>
* Create a link
User space can create a link between two entities with:
$ mkdir
/configfs/vimc/vimc0/links/<entity_src_name>:<pad_n>-><entity_sink_name>:<pad_n>
Example:
$ mkdir /configfs/vimc/vimc0/links/DebayerA:1->Scaler:0
$ ls -l /configfs/vimc/vimc0/links/DebayerA:1->Scaler:0
flags
mkdir will be rejected if folder is not on the format
<entity_src_name>:<pad_n>-><entity_sink_name>:<pad_n>.
mkdir will be rejected if either <entity_src_name> or <entity_sink_name>
are not found in /configfs/vimc/vimc0/entities/
The link will only be created if both entities are in "plugged" state.
When an entity is removed from /configfs/vimc/vimc0/entities/ with
rmdir, its corresponding link folders at
/configfs/vimc/vimc0/links will be automatically removed.
If one of the entities changes from "plugged" to "unplugged", the link
is only removed from the media
representation, the link folder won't be removed.
flags can be one of "", "enabled", "immutable", "dynamic",
"dynamic,enabled".
flags cannot be changed if the link was already created in the media
controller, to alter it unplug the
device through /configfs/vimc/vimc0/hotplug or unplug one of the source
or sink entities connected to the
link through its hotplug file.
flags are of type "" by default.
