OMAP4 framebuffer

Stefan Kalkowski stefan.kalkowski at ...1...
Fri Jul 13 12:02:55 CEST 2012

Hi Ivan,

On 13.07.2012 08:11, Ivan Loskutov wrote:
> Hello.
> I try to extend OMAP4 frame-buffer driver for using with LCD. Your HDMI
> example does not work. I try to read OMAP DSS registers and receive
> strange values, for example: value DSS_REVISION is 0x02100004, other DSS
> and DISPC registers has similar values. What version u-boot do you use
> on pandaboard? Maybe part of the initialization is performed in u-boot.

one issue is that currently the outer L2-cache isn't handled by
Fiasco.OC (for the pandaboard). That means as long as it's enabled
(already by u-boot) it will contaminate DMA regions used by the
LCD-driver, that were already in the cache before.

So one interim fix is to use an u-boot version which doesn't enable the
L2-cache (CONFIG_SYS_L2CACHE_OFF variable in u-boot config). It doesn't
explains the observed strange register values, but maybe this already
enables you to use the LCD?

We are still working at that L2-cache issue. First steps are done to
enable L2-cache invalidation in Fiasco.OC, but there are some problems
left. So please by now disable the L2-cache on the Pandaboard completely
before using any DMA driven devices (USB-networking and LCD).

Best regards

PS: a ready to use u-boot image can be found here:

> --
> Ivan Loskutov
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Stefan Kalkowski
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