Re: [PATCH v5] Driver for ON Semi AR0521 camera sensor

[Krzysztof Hałasa]

Jacopo Mondi <jacopo@xxxxxxxxxx> writes:

>> This is BTW completely orthogonal to the -EBUSY on set_fmt(). The
>> effects will be exactly the same if the e.g. geometry changes come when
>> the sensor is not streaming.
>>
>
> No, this isn't true. Your s_fmt() implementation stops then restart the
> stream. It has an undocumented side effect and will cause undefined
> behaviour.

It will cause *at*most* a corrupted frame. On a MIPI link. That's right.
Such a corrupted frame will *at*most* cause some transient IO error - it
must not cause anything serious, because corrupted frames on MIPI can
happen for multiple reasons, some of which simply cannot be avoided.
BTW I will see if it's actually the case - chances are, there is no
corruption, but I tested it years ago and haven't yet checked my notes.

In fact those set_fmt() in other drivers may - or may not - cause
corrupted frames just the same.

> If your s_fmt() has to stop and restart streaming to take effect,
> it means userspace should instead stop the stream, change
> the format where opportune in the pipeline, and then restart the
> stream.

Maybe. This is a sensor driver - not userspace.
If the userspace uses it as a part of "frame grabber", it will certainly
do exactly that (nothing else would make sense in practice).

Unfortunately this all will have to wait a bit, so thanks for your help,
expect a new patch in few weeks.
-- 
Krzysztof "Chris" Hałasa

Sieć Badawcza Łukasiewicz
Przemysłowy Instytut Automatyki i Pomiarów PIAP
Al. Jerozolimskie 202, 02-486 Warszawa