Questions about tripple display

Questions about tripple display

[Guo Tang]

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Hi, 
Greetings!

I have a system with GM 45 chip set. I want to have 3 displays: LVDS, VGA, and TV output. There is no need for 
them to show different contents. So only clone display is required. From GM 45 chip set spec, looks like only 2 
display ports can be active at the same time. Is it possible to modify driver to get 3 clone displays? Any suggestion 
to where in the driver/Kernel I can poke around would be appreciated.

Thanks,
Guo

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Re: Questions about tripple display

[Daniel Vetter]

On Fri, Jul 13, 2012 at 5:59 PM, Guo Tang <guo.tang@sonoartis.com> wrote:
> Hi,
> Greetings!
>
> I have a system with GM 45 chip set. I want to have 3 displays: LVDS, VGA,
> and TV output. There is no need for
> them to show different contents. So only clone display is required. From GM
> 45 chip set spec, looks like only 2
> display ports can be active at the same time. Is it possible to modify
> driver to get 3 clone displays? Any suggestion
> to where in the driver/Kernel I can poke around would be appreciated.

This does not work, because both LVDS and TV run on a fixed clock
(which does not necessarily agree with the dotclock of the mode),
hence you can't clone them. At least not in all cases, and imo trying
to support such a configuration in more cases is wasted effort. If you
need to drive that many outputs, you're not in the market of a low-end
igd solution like gm45 imho.

Cheers, Daniel
-- 
Daniel Vetter
daniel.vetter@ffwll.ch - +41 (0) 79 364 57 48 - http://blog.ffwll.ch

Re: Questions about tripple display

[Guo Tang]

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Hi, Daniel,

Thanks for the prompt reply. From your reply looks like I still have a
little hope.

How about if I only run 1024x768@60Hz or 30Hz resolution? Will that address
the dotclock problem
between LVDS and TV?

Thanks,
Guo

On Fri, Jul 13, 2012 at 9:10 AM, Daniel Vetter <daniel@ffwll.ch> wrote:

> On Fri, Jul 13, 2012 at 5:59 PM, Guo Tang <guo.tang@sonoartis.com> wrote:
> > Hi,
> > Greetings!
> >
> > I have a system with GM 45 chip set. I want to have 3 displays: LVDS,
> VGA,
> > and TV output. There is no need for
> > them to show different contents. So only clone display is required. From
> GM
> > 45 chip set spec, looks like only 2
> > display ports can be active at the same time. Is it possible to modify
> > driver to get 3 clone displays? Any suggestion
> > to where in the driver/Kernel I can poke around would be appreciated.
>
> This does not work, because both LVDS and TV run on a fixed clock
> (which does not necessarily agree with the dotclock of the mode),
> hence you can't clone them. At least not in all cases, and imo trying
> to support such a configuration in more cases is wasted effort. If you
> need to drive that many outputs, you're not in the market of a low-end
> igd solution like gm45 imho.
>
> Cheers, Daniel
> --
> Daniel Vetter
> daniel.vetter@ffwll.ch - +41 (0) 79 364 57 48 - http://blog.ffwll.ch
>

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Re: Questions about tripple display

[Daniel Vetter]

On Fri, Jul 13, 2012 at 6:36 PM, Guo Tang <guo.tang@sonoartis.com> wrote:
> Hi, Daniel,
>
> Thanks for the prompt reply. From your reply looks like I still have a
> little hope.
>
> How about if I only run 1024x768@60Hz or 30Hz resolution? Will that address
> the dotclock problem
> between LVDS and TV?

As I've said, carefully picking a dotclock that matches up with TV or
LVDS can work, but we don't bother to support that in the driver
because imo it's not worth the hassle. If you really want to stitch
something like this together, grep for needs_tvclock in the drm/i915
sources (or check out the lvds panel fitter code). I.e. it's by far
not as simple as just picking the same mode as e.g. on the TV. And
you'd need to restructure the kernel driver quite a bit to make it
work.
-Daniel
-- 
Daniel Vetter
daniel.vetter@ffwll.ch - +41 (0) 79 364 57 48 - http://blog.ffwll.ch

Re: Questions about tripple display

[Guo Tang]

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Great! Thanks for the direction. We will give it a shoot!

- Guo

On Fri, Jul 13, 2012 at 9:38 AM, Daniel Vetter <daniel@ffwll.ch> wrote:

> On Fri, Jul 13, 2012 at 6:36 PM, Guo Tang <guo.tang@sonoartis.com> wrote:
> > Hi, Daniel,
> >
> > Thanks for the prompt reply. From your reply looks like I still have a
> > little hope.
> >
> > How about if I only run 1024x768@60Hz or 30Hz resolution? Will that
> address
> > the dotclock problem
> > between LVDS and TV?
>
> As I've said, carefully picking a dotclock that matches up with TV or
> LVDS can work, but we don't bother to support that in the driver
> because imo it's not worth the hassle. If you really want to stitch
> something like this together, grep for needs_tvclock in the drm/i915
> sources (or check out the lvds panel fitter code). I.e. it's by far
> not as simple as just picking the same mode as e.g. on the TV. And
> you'd need to restructure the kernel driver quite a bit to make it
> work.
> -Daniel
> --
> Daniel Vetter
> daniel.vetter@ffwll.ch - +41 (0) 79 364 57 48 - http://blog.ffwll.ch
>

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