Hi Stefano,
On 07/26/2013 01:43 AM, Stefano Babic wrote:
Hi Robert, Anatolji,
On 26/07/2013 09:50, Anatolij Gustschin wrote:
I realize that there's already the FDT and CONFIG_OF_CONTROL functionality and device trees sort of cover the passing to Linux part so maybe before handing it off, converting the relevant data into a device tree that Linux can already use/parse would work.
Devicetree bindings for describing display timings info exist in recent Linux kernel versions (since v3.9 I think) and are documented under Documentation/devicetree/bindings/video/display-timing.txt. In Linux there are also DT helpers to parse display timings nodes and read the timing values into fb_videomode structure (of_get_display_timings, of_get_fb_videomode). Code for adding such display timings nodes to the device tree under U-Boot doesn't exist yet.
IMHO adopting DT looks very interesting, as it can really simplify sharing configuration between u-boot and kernel. On i.MX6 we have not yet started to use DT to configure u-boot as it is already done on other SOCs (Tegra), but it seems to me the right way to do.
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.
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.
Is Tegra somehow using DT to configure U-Boot display? I'm not finding the code.
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.
Please advise,
Eric