Re: [Media Summit] Imaging Sensor functionality

[Laurent Pinchart <laurent.pinchart@ideasonboard.com>]

Hi Dave,

On Tue, Sep 06, 2022 at 08:53:41PM +0300, Laurent Pinchart wrote:
> On Tue, Sep 06, 2022 at 05:14:30PM +0100, Dave Stevenson wrote:
> > Hi All.
> > 
> > I realise that I'm in a slightly different position from many mainline
> > Linux-media developers in that I see multiple use cases for the same
> > sensor, rather than a driver predominantly being for one
> > product/platform. I'm therefore wanting to look at generic solutions
> > and fully featured drivers. Users get to decide the use cases, not the
> > hardware designers.
> 
> Could you clarify here what you mean by users and hardware designers ?
> Users can be understood as
> 
> - Users of the camera sensor, i.e. OEMs designing a product
> - Users of the hardware platform , i.e. software developers writing
>   applications
> - Users of the software, i.e. end-users
> 
> Hardware designers could then equally mean
> 
> - Sensor vendors
> - SoC vendors
> - Board vendors
> - Product vendors
> 
> > The issues I've raised are things that I've encountered and would
> > benefit from a discussion to get views as to the direction that is
> > perceived to be workable. I appreciate that some can not be solved
> > immediately, but want to avoid too much bikeshedding in the first
> > round of patches.
> > What's realistic, and what pitfalls/limitations immediately jump out at people.
> > 
> > Slides are at https://drive.google.com/file/d/1vjYJjTNRL1P3j6G4Nx2ZpjFtTBTNdeFG/view?usp=sharing
> 
> Thank you, I will review that ASAP.

A few questions:

- Regarding the sensor synchronization, are you considering the trigger
  signal as signaling the beginning of exposure only, or also use cases
  where it controls the exposure duration ?

- For VCM ringing reduction and standardization of parameters, are there
  examples you could share to explain this in more details, with the
  type of parameters that need to be specified ?

And one comment. On slide 20/23, you wrote

  Likely to produce a load of boilerplate in all drivers. Abstract out
  an image sensor pinctrl helper?

I think we need more than that, we need a large helper for camera
sensors (in particular for raw sensors) that will bridge the large gap
between the sensor and the V4L2 subdev API. There's too much boilerplate
code already, and worse, different sensor drivers exposing the same
feature to userspace in different ways.

> > See you on Monday.

-- 
Regards,

Laurent Pinchart