Re: [RFC 00/17] OMAPDSS: Change way of passing timings from panel driver to interface

[Tomi Valkeinen <tomi.valkeinen@ti.com>]

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On Wed, 2012-08-08 at 14:08 +0530, Archit Taneja wrote:
> On Wednesday 08 August 2012 01:43 PM, Tomi Valkeinen wrote:
> > On Wed, 2012-08-08 at 13:29 +0530, Archit Taneja wrote:
> >
> >> Okay, one thing which I want to align on is that most of these functions
> >> don't really do the actual configurations. That is, they'll just update
> >> the private data, and the actual configuration will only happen on enable.
> >>
> >> We would want set_timings() op to have a direct impact. But we wouldn't
> >> want the same for setting the data lines, that could be clubbed with
> >> other configurations at enable. That's okay, right?
> >
> > I'm not sure we want/need set_timings to have direct impact. Changing
> > the timings on the fly has some problems, like the output size changing
> > to smaller than the overlays, and we perhaps may need to adjust the
> > clock dividers (dispc's, DSI PLL's or PRCM's).
> >
> > It feels just much easier and safer to require that the mgr is disabled
> > when these changes are made. And as far as I can see, there shouldn't be
> > any need to change the timings via the shadow registers, as quickly as
> > possible and during vblank...
> 
> That makes sense. But currently set_timings for DPI has a direct impact. 
> HDMI/VENC/SDI take the easier route of disabling and enabling the interface.
> 
> I agree it's safer and easier to make sure things are disabled first, 
> but maybe it's good to have the capability set hdmi timings on the fly 
> in the future, it would make the switch faster, same goes for reading edid.

When do we need to switch mode quickly? Reading edid should not require
disabling the output for sure.

HDMI is a bit broken currently, though. I think we first enable the
whole stuff, including video output using VGA, then we read EDID, then
we change the mode.

We should just enable enough of HDMI to be able to read EDID, and start
the video output with the correct mode. This needs some restructuring of
the driver, though. I tried it once quickly, but it turned out not to be
trivial.

> What I meant to ask was whether we should do the same for something like 
> dpi_set_data_lines(), that is, disable dpi, update the data_lines 
> private data with a new value, and enable dpi again.

Hmm, I think it's better to leave disabling and enabling the output to
the panel driver. So when the panel driver wants to use
dpi_set_data_lines(), it needs to first disable the DPI output. If it
doesn't, dpi_set_data_lines() returns -EBUSY.

Otherwise if the panel driver does something like:

dpi_set_foo()
dpi_set_bar()

Both of those could first disable output, change setting, enable output.
Instead the panel should first disable, then call those, and then
enable.

 Tomi


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