Hi,
On 07/26/2011 11:26 AM, Hans Verkuil wrote:
OK, I'm back to work after my vacation, so it's time to go through the
backlog...
Welcome back :)
On Tuesday, July 12, 2011 15:25:02 Hans de Goede wrote:
Hi,
On 07/04/2011 11:43 AM, Hans Verkuil wrote:
<snip snip>
It is relevant. Take an application that saves the current state of all
controls and restores it the next time it is started. If you report the
device's autogain value instead of the manual gain, then that manual gain
value is lost. I consider this a major drawback.
If autogain is on, then the gain is RO, so it should not be saved. Let alone
restored.
Marking gain as inactive is fine, but marking it as read-only is not so clear.
Currently the RO flag is static. This allows control panels to use e.g. a text
field instead of an input field to show the value.
I would like to keep that functionality. If we make the RO flag dynamic, then
GUIs won't know whether to show it as a disabled input field or as a text field.
Whereas with the inactive flag they will know that it has to be a disabled
input field.
Agreed, where I wrote read only I meant inactive, which does make it less clear
that the control should not be saved / restored by a save / restore app.
When the inactive flag is set, it is still allowed to set the value. However,
if we add a volatile flag as well, then we may want to have the combination
'inactive and volatile' return an error when an application attempts to set the
value.
I think that is a good solution to indicate dynamic-readonly ness (more or less),
and thus to indicate that the control should not be written (and thus not saved/
restored).
Or is this too complex and should we just discard the value in a case like that?
I would prefer returning an error, so that things don't silently fail, also
unless we actually return an error many apps are likely to get this wrong.
<snip snip>
I still believe that everything boils down to 2 possible scenarios,
and the rest follows from that. With the 2 scenarios being:
1) There is a manual setting which is constant until explicitly
changed, when (ie) gain switches from auto mode to manual mode
then the actual used gain is reset to this manual setting
2) There is a single gain setting / register, which is r/w when the
control is in manual mode and ro when in auto mode. When auto mode
gets switched off, the gain stays at the last value set by auto mode.
2) Is what most webcam sensors (and the pwc firmware) implement at
the hardware level, and what to me also makes the most sense for webcams.
To me this whole discussion centers around these 2 scenarios, with you
being a proponent of 1), and I guess that for video capture boards 1 makes
a lot of sense, and me being a proponent of 2.
Proposal: lets agree that these 2 methods of handling autofoo controls
both exist and both have merits in certain cases, this means letting
it be up to the driver to choose which method to implement.
OK.
If we can agree on this, then the next step would be to document both
methods, as well as how the controls should behave in either scenario.
I'm willing to write up a first draft for this.
I can do that as well, see below.
Ah great, you just saved me some work I always like it when people
save me work :)
<snip snip>
I think we need to agree that we disagree :)
Actually, I agree with much of what you wrote :-)
Good :)
OK, so we have two scenarios:
1) There is a manual setting which is constant until explicitly changed, when e.g.
gain switches from auto mode to manual mode then the actual used gain is reset to
this manual setting.
In this case the e.g. gain control is *not* marked volatile, but just inactive.
If the hardware can return the gain as set by the autogain circuit, then that has
to be exported as a separate read-only control (e.g. 'Current Gain').
2) There is a single gain setting / register, which is active when the control is in
manual mode and inactive and volatile when in auto mode. When auto mode gets switched
off, the gain stays at the last value set by auto mode.
This scenario is only possible, of course, if you can obtain the gain value as set
by the autogain circuitry.
I fully agree with the above, +1
An open question is whether writing to an inactive and volatile control should return
an error or not.
I would prefer an error return.
Webcams should follow scenario 2 (if possible).
It is less obvious what to recommend for video capture devices. I'd leave it up to
the driver for now.
Sounds good to me.
Regards,
Hans
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