HDMI on i.MX6

HDMI on i.MX6

[Gary Thomas]

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I have some questions about HDMI display on i.MX6, the
SabreLite / Nitrogen6x in particular.

When I boot with my HDMI monitor attached, U-Boot finds it
and tells me:
   auto-detected panel HDMI
   Display: HDMI (1024x768)

Then Linux is booted with these arguments:
   video=mxcfb0:dev=hdmi,1280x720M@60,if=RGB24
I know that these parameters come from the boot script, but
they seem to be hard coded.  What if I wanted different display
parameters?  These values don't seem to work very well for my
monitor - stuff is being cut off on all edges.  Perhaps my
monitior isn't the best so I'd like some guidance on how to
tune things.  I've attached a picture of the actual screen
so you can see what I mean.

Thanks

-- 
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Gary Thomas                 |  Consulting for the
MLB Associates              |    Embedded world
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Re: HDMI on i.MX6

[Eric Nelson]

Hi Gary,

On 06/02/2014 01:07 PM, Gary Thomas wrote:
> I have some questions about HDMI display on i.MX6, the
> SabreLite / Nitrogen6x in particular.
>
> When I boot with my HDMI monitor attached, U-Boot finds it
> and tells me:
>    auto-detected panel HDMI
>    Display: HDMI (1024x768)
>

This is done because the display clocking is currently wonky
in U-Boot (you can have any frequency as long as it's the same
as the Hannstar display).

> Then Linux is booted with these arguments:
>    video=mxcfb0:dev=hdmi,1280x720M@60,if=RGB24

;) We chose that resolution just to mess with you.

This is currently hard-coded in the boot script here:

	https://github.com/boundarydevices/u-boot-imx6/blob/production/board/boundary/nitrogen6x/6x_bootscript-yocto.txt#L15

> I know that these parameters come from the boot script, but
> they seem to be hard coded.  What if I wanted different display
> parameters?  These values don't seem to work very well for my
> monitor - stuff is being cut off on all edges.  Perhaps my
> monitior isn't the best so I'd like some guidance on how to
> tune things.  I've attached a picture of the actual screen
> so you can see what I mean.
>

No problem. You can figure out what resolution works well with
your display by echo'ing values to /sys/class/graphics/fb0/mode
(cat /sys/class/graphics/fb0/modes for the values supported
by your monitor).

Then you can update the boot script .txt file and convert to
binary using this tool:

	http://git.boundarydevices.com/bootscript.php

In order to integrate with a Yocto build, you'll want to
generate a patch that overrides things in u-boot-script-boundary:
	https://github.com/Freescale/meta-fsl-arm-extra/blob/master/recipes-bsp/u-boot/u-boot-script-boundary_git.bb

Regards,


Eric