Re: Weird default vblank value in ov5693

[Hans de Goede <hdegoede@redhat.com>]

Hi,

On 1/29/24 09:58, Jacopo Mondi wrote:
> Hi Hans
> 
> On Sun, Jan 28, 2024 at 09:58:41PM +0100, Hans de Goede wrote:
>> Hi All,
>>
>> While adding vblank ctrl support to the ov2680 driver I was looking
>> at the vblank ctrl code in the ov5693 and I noticed something
>> which I believe is weird / undesirable.
>>
>> When setting a new mode the ov5693 driver does not keep the current
>> vts value (adjusting vblank to keep vts and thus the framerare and
>> exposure unchanged).
>>
>> Instead it calculates a new vts value, resetting the framerate
>> to 30 fps; or 60 fps for smaller resolutions and then sets
>> vblank to the new (vts - new_mode->height) and adjusts
>> the exposure control-range to fit within the new vts, potentially
>> also changing the exposure value.
>>
>> This behavior of the ov5693 code means that switching resolution
>> also changes the framerate and the exposure value which seems
>> undesirable.
>>
>> The vblank and hblank control values changes on setting a mode
>> is unavoidable but the framerate and exposure value changing
>> at the same time seems undesirable.
>>
>> Note that this also halves the max supported exposure value
>> when going to a lower-res mode even when userspace never
>> touches the vblank control.
>>
> 
> Would you be interested in reviewing
> https://patchwork.kernel.org/project/linux-media/list/?series=697777&state=%2A&archive=both
> 
> and discuss there what the desired behaviour should be ?

I'm definitely interested in discussing this and in
helping with reviewing the documentation patches,
good timing wrt writing those patches :)

but Dan already replied in this thread, so lets
keep the discussion in this thread for now ?

Also I think this will probably make a good agenda
item for the libcamera workshop coming Friday ?

Hopefully we can make some decisions about this there
and then I can help with reviewing revised documentation
patches after that.

Regards,

Hans