Hi Hans!
Thanks for the patchset! It looks quite good at first sight, a few comments
and
questions follow though.
On Monday, November 13, 2017 11:34:02 PM JST, Hans Verkuil wrote:
From: Hans Verkuil <hans.verkuil@xxxxxxxxx>
Hi Alexandre,
This is a first implementation of the request API in the
control framework. It is fairly simplistic at the moment in that
it just clones all the control values (so no refcounting yet for
values as Laurent proposed, I will work on that later). But this
should not be a problem for codecs since there aren't all that many
controls involved.
Regarding value refcounting, I think we can probably do without it if we
parse
the requests queue when looking values up. It may be more practical (having
a
kref for each v4l2_ctrl_ref in a request sounds overkill to me), and maybe
also
more predictible since we would have less chance of having dangling old
values.
The API is as follows:
struct v4l2_ctrl_handler *v4l2_ctrl_request_alloc(void);
This allocates a struct v4l2_ctrl_handler that is empty (i.e. has
no controls) but is refcounted and is marked as representing a
request.
int v4l2_ctrl_request_clone(struct v4l2_ctrl_handler *hdl,
const struct v4l2_ctrl_handler *from,
bool (*filter)(const struct v4l2_ctrl *ctrl));
Delete any existing controls in handler 'hdl', then clone the values
from an existing handler 'from' into 'hdl'. If 'from' == NULL, then
this just clears the handler. 'from' can either be another request
control handler or a regular control handler in which case the
current values are cloned. If 'filter' != NULL then you can
filter which controls you want to clone.
One thing that seems to be missing is, what happens if you try to set a
control
on an empty request? IIUC this would currently fail because find_ref()
would
not be able to find the control. The value ref should probably be created
in
that case so we can create requests with a handful of controls.
Also, if you clone a handler that is not a request, I understand that all
controls will be deduplicated, creating a full-state copy? That could be
useful,
but since this is the only way to make the current code work, I hope that
the
current impossibility to set a control on an empty request is a bug (or
misunderstanding from my part).
void v4l2_ctrl_request_get(struct v4l2_ctrl_handler *hdl);
Increase the refcount.
void v4l2_ctrl_request_put(struct v4l2_ctrl_handler *hdl);
Decrease the refcount and delete hdl if it reaches 0.
void v4l2_ctrl_request_setup(struct v4l2_ctrl_handler *hdl);
Apply the values from the handler (i.e. request object) to the
hardware.
You will have to modify v4l_g/s/try_ext_ctrls in v4l2-ioctls.c to
obtain the request v4l2_ctrl_handler pointer based on the request
field in struct v4l2_ext_controls.
The first patch in this series is necessary to avoid cloning
controls that belong to other devices (as opposed to the subdev
or bridge device for which you make a request). It can probably
be dropped for codecs, but it is needed for MC devices like
omap3isp.
This series has only been compile tested! So if it crashes as
soon as you try to use it, then that's why :-)
Note: I'm not sure if it makes sense to refcount the control
handler, you might prefer to have a refcount in a higher-level
request struct. If that's the case, then I can drop the _get
function and replace the _put function by a v4l2_ctrl_request_free()
function.
That's exactly what I thought when I saw the refcounting. This is probably
a
problem for later since we want to focus on codecs for now, but I think we
will
ultimately want to manage refcounting outside of v4l2_ctrl_handler. Maybe a
higher-level request class of which the current control-framework based
design
would be an implementation. I am thinking about IPs like the VSP1 which
will
probably want to model the controls either in a different way, or at least
to
add extra data beyond the controls.
All in all I think I can use this for codecs. I am still trying to shoehorn
my
first version into the media stuff, and to nobody's surprise this is not
that
easy. :P But the fact the control framework part is already mostly taken
care
of greatly helps.
Thanks!
Alex.
