On Mon 2017-03-13 10:45:38, Russell King - ARM Linux wrote:

On Mon, Mar 13, 2017 at 11:02:34AM +0100, Hans Verkuil wrote:

quoted

On 03/11/2017 07:14 PM, Steve Longerbeam wrote:

quoted

The event must be user visible, otherwise the user has no indication
the error, and can't correct it by stream restart.

In that case the driver can detect this and call vb2_queue_error. It's
what it is there for.

The event doesn't help you since only this driver has this issue. So nobody
will watch this event, unless it is sw specifically written for this SoC.

Much better to call vb2_queue_error to signal a fatal error (which this
apparently is) since there are more drivers that do this, and vivid supports
triggering this condition as well.

So today, I can fiddle around with the IMX219 registers to help gain
an understanding of how this sensor works.  Several of the registers
(such as the PLL setup [*]) require me to disable streaming on the
sensor while changing them.

This is something I've done many times while testing various ideas,
and is my primary way of figuring out and testing such things.

Whenever I resume streaming (provided I've let the sensor stop
streaming at a frame boundary) it resumes as if nothing happened.  If I
stop the sensor mid-frame, then I get the rolling issue that Steve
reports, but once the top of the frame becomes aligned with the top of
the capture, everything then becomes stable again as if nothing happened.

The side effect of what you're proposing is that when I disable streaming
at the sensor by poking at its registers, rather than the capture just
stopping, an error is going to be delivered to gstreamer, and gstreamer
is going to exit, taking the entire capture process down.

This severely restricts the ability to be able to develop and test
sensor drivers.

Well, but kernel should do what is best for production, not what is
best for driver debugging.

And yes, I guess you can have #ifdef or module parameter or something
switching for behaviour you prefer when you are debugging. But for
production, vb2_queue_error() seems to be the right solution.

								Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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