reading config parameters of omap3-isp subdevs

reading config parameters of omap3-isp subdevs

[Michael Jones]

Hi all,

I am playing around with some parameters in the previewer on the ISP. 
With ioctl VIDIOC_OMAP3ISP_PRV_CFG I am able to write the various 
parameters but what I'm missing is a way to read them.  For example, I 
have no way to adjust only coef2 in 'struct omap3isp_prev_wbal' while 
leaving the others unchanged.  If I could first read the whole 
omap3isp_prev_wbal structure, then I could change just the things I want 
to change.  This seems like it would be common functionality for such 
ioctls.  I didn't find any previous discussion related to this.

I could imagine either adding a r/w flag to 'struct 
omap3isp_prev_update_config' or adding a new ioctl entirely.  I think I 
would prefer the r/w flag.  Feedback?

I noticed that other ISP subdevs have similar ioctls.  Perhaps a similar 
thing would be useful there, but right now I'm only looking at the 
previewer.

-Michael

MATRIX VISION GmbH, Talstrasse 16, DE-71570 Oppenweiler
Registergericht: Amtsgericht Stuttgart, HRB 271090
Geschaeftsfuehrer: Gerhard Thullner, Werner Armingeon, Uwe Furtner, Erhard Meier

Re: reading config parameters of omap3-isp subdevs

[Laurent Pinchart]

Hi Michael,

On Friday 16 March 2012 15:06:15 Michael Jones wrote:
> Hi all,
> 
> I am playing around with some parameters in the previewer on the ISP. With
> ioctl VIDIOC_OMAP3ISP_PRV_CFG I am able to write the various parameters but
> what I'm missing is a way to read them. For example, I have no way to adjust
> only coef2 in 'struct omap3isp_prev_wbal' while leaving the others
> unchanged. If I could first read the whole omap3isp_prev_wbal structure,
> then I could change just the things I want to change. This seems like it
> would be common functionality for such ioctls. I didn't find any previous
> discussion related to this.
> 
> I could imagine either adding a r/w flag to 'struct
> omap3isp_prev_update_config' or adding a new ioctl entirely. I think I
> would prefer the r/w flag.  Feedback?
> 
> I noticed that other ISP subdevs have similar ioctls.  Perhaps a similar
> thing would be useful there, but right now I'm only looking at the
> previewer.

Adding a R/W bit to the flag argument should indeed work. However, I'm 
wondering what your use case for reading parameters back is. The preview 
engine parameter structures seem pretty-much self-contained to me, I'm not 
sure it would make sense to only modify one of the parameters.

-- 
Regards,

Laurent Pinchart

Re: reading config parameters of omap3-isp subdevs

[Michael Jones]

Hi Laurent,

On 03/20/2012 12:22 AM, Laurent Pinchart wrote:
> Hi Michael,
>
> On Friday 16 March 2012 15:06:15 Michael Jones wrote:
[snip]
>
> Adding a R/W bit to the flag argument should indeed work. However, I'm
> wondering what your use case for reading parameters back is.

The simplest use case in my mind is that after the user has fiddled 
around with config parameters, they should be able to set them back to 
their original state.  For that, they need to know what the original 
state was.

 > The preview
> engine parameter structures seem pretty-much self-contained to me, I'm not
> sure it would make sense to only modify one of the parameters.

Why doesn't it make sense to write to only e.g. 'COEF3' in the 
PRV_WBGAIN register?  Especially considering the sparse documentation of 
many of these registers, I would like to be able to tweak the existing 
parameters from their defaults, rather than start from scratch.

-Michael

MATRIX VISION GmbH, Talstrasse 16, DE-71570 Oppenweiler
Registergericht: Amtsgericht Stuttgart, HRB 271090
Geschaeftsfuehrer: Gerhard Thullner, Werner Armingeon, Uwe Furtner, Erhard Meier

Re: reading config parameters of omap3-isp subdevs

[Laurent Pinchart]

Hi Michael,

On Tuesday 20 March 2012 11:06:56 Michael Jones wrote:
> On 03/20/2012 12:22 AM, Laurent Pinchart wrote:
> > On Friday 16 March 2012 15:06:15 Michael Jones wrote:
> [snip]
> 
> > Adding a R/W bit to the flag argument should indeed work. However, I'm
> > wondering what your use case for reading parameters back is.
> 
> The simplest use case in my mind is that after the user has fiddled around
> with config parameters, they should be able to set them back to their
> original state. For that, they need to know what the original state was.
> 
> > The preview engine parameter structures seem pretty-much self-contained to
> > me, I'm not sure it would make sense to only modify one of the parameters.
> 
> Why doesn't it make sense to write to only e.g. 'COEF3' in the PRV_WBGAIN
> register? Especially considering the sparse documentation of many of these
> registers, I would like to be able to tweak the existing parameters from
> their defaults, rather than start from scratch.

Because configuring white balance requires modifying all the coefficients.

I agree that querying the default parameters can be useful for experimentation 
purpose, although in that case you could just have a look at the driver source 
code ;-) I've sent a patch that modifies the way the preview engine handles 
the configuration process to the linux-media mailing list. I could try 
implementing read access on top of that, but I'm not sure when I'll have time 
to do so. If you want to give it a try, I'll review your code :-) Be careful 
of the race conditions, they're not trivial.

-- 
Regards,

Laurent Pinchart

Re: reading config parameters of omap3-isp subdevs

[Joshua Hintze]

I was just wondering the same thing as far as reading the current
settings. The reason why I would want to read the settings (could be
different than Michael's) is that there are a lot of settings that I
am still unfamiliar with yet. I don't know the default values. So by
being able to read the entire settings and adjust only the white
balance gain or such would make the learning process considerably less
sharp. I would love to have the read option.

Josh


Hi Michael,

On Friday 16 March 2012 15:06:15 Michael Jones wrote:
> Hi all,
>
> I am playing around with some parameters in the previewer on the ISP. With
> ioctl VIDIOC_OMAP3ISP_PRV_CFG I am able to write the various parameters but
> what I'm missing is a way to read them. For example, I have no way to adjust
> only coef2 in 'struct omap3isp_prev_wbal' while leaving the others
> unchanged. If I could first read the whole omap3isp_prev_wbal structure,
> then I could change just the things I want to change. This seems like it
> would be common functionality for such ioctls. I didn't find any previous
> discussion related to this.
>
> I could imagine either adding a r/w flag to 'struct
> omap3isp_prev_update_config' or adding a new ioctl entirely. I think I
> would prefer the r/w flag.  Feedback?
>
> I noticed that other ISP subdevs have similar ioctls.  Perhaps a similar
> thing would be useful there, but right now I'm only looking at the
> previewer.

Adding a R/W bit to the flag argument should indeed work. However, I'm
wondering what your use case for reading parameters back is. The preview
engine parameter structures seem pretty-much self-contained to me, I'm not
sure it would make sense to only modify one of the parameters.

-- 
Regards,

Laurent Pinchart