[U-Boot] [RFC] Remove static display data

[Stefano Babic <sbabic@denx.de>]

Hi Eric,

On 26/07/2013 16:04, Eric Nelson wrote:

> 
> The real question we have regarding DT is the timing. We're shipping
> DT files on secondary storage (SATA/SD card), and want/need something
> local (i.e. env in SPI-NOR) to present a U/I if either no storage
> available or if something goes wrong.

ok, understood.

> 
> A secondary need/desire is to have something simple for configuring
> a new display. The process of tuning some of the parameters (esp
> margins) can sometimes be iterative because the data sheets aren't
> always clear and clock options are often imprecise. Since this
> iteration and configuration is often done by EEs in a lab who
> don't have an easy way to recompile a DTS, our inclination is
> to do something locally.

ok, I understand the point. Maybe it should be even more simple for the
EEs if the would be such kind of special u-boot commands, able to set
the timing and reload the framebuffer.

Can be a solution using the u-boot's fdt library enough ? With "fdt get"
and "fdt set" it  is possible to read and modify a DT in memory, and
then the modified DT can be stored back - avoiding to compile directly
the DTS.

> 
> Is Tegra somehow using DT to configure U-Boot display?
> I'm not finding the code.

./board/compal/dts/tegra20-paz00.dts seems doing that, but I have no
experience with it ;(

My thoughts are more related by comparing what the kernel does and how
the timing is configured. There are several examples (I am seeing the
imx23-dts, but it is not the only one) where the complete timing for a
panel is done inside the DT.

As you have already checked, using a U-Boot variable has some
limitations, because it does not contain all parameters that are needed.
And I think it could be quite difficult to get it general for all SOCs
because some SOCs need some specialties (VRAM for OMAP could be an example).

> No matter how we end up doing this, passing U-Boot's display
> setup to the kernel via DT is the **right thing**, so that
> there aren't two bits to maintain.

Yes, I think we do not need to discuss how to pass to the kernel - but I
am checking if it is a suitable way to configure the u-boot display,too.
Anyway, I agree that using a U-Boot variable is much more simple to
implement..

Best regards,
Stefano

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