Re: [RFC 1/4] video: panel: add CLAA101WA01A panel support

On Thu, Jan 31, 2013 at 12:51 PM, Mark Zhang [off-list ref] wrote:

quoted

DDC access is a property of the display controller, not the panel
itself. The panel might be hooked up to a display controller's DDC/I2C
channel as the target, but it isn't the host/controller of the DDC/I2C
channel. As such, placing the nvidia,ddc property into the display
controller node makes sense.

Yes, DC triggers the DDC access and is the host of the DDC/I2C channel.
So I think it's reasonable to put nvidia,ddc property into the display
controller node. But the video mode info in EDID which be fetched via
DDC is the property of the panel, so this info should be provided by
panel driver. Actually display controller cares about the video modes,
not the way to get these info. So I think it's better to do the whole
work like this:

1) display controller relied on CDF to call "display_entity_get_modes"
2) panel driver calls the function which is hooked to display controller
to get the video modes via DDC.
3) if the video modes can't be fetched via DDC, panel driver provides
the info(either by hard-coded or defined in DT) anyway

This would require a callback dedicated to this in display_entity and
would break its simple design.

Just like I said above, display controller should not query DDC
directly. Since CDF already defines these for us, display controller
should call CDF's functions, like: display_entity_get_modes,
display_entity_get_size... I think this is the key difference I wanna
talk about. And also in this way, display controller doesn't need to
care about this 2 steps logics, just call "display_entity_get_modes" is OK.

Well the fact is that it *is* the display controller that queries DDC
directly. The panel is just a bus here, and the EDID EEPROM could
perfectly work without it. If you model what you described with DT
nodes, I'm afraid you will end up with something both complex (with DC
node referencing panel node and back again for the EDID bus) and that
does not picture reality accurately.

Alex.