[Letux-kernel] DSI panels with omapdrm on 4.20-rc

Tomi Valkeinen tomi.valkeinen at ti.com
Tue Dec 18 15:24:23 CET 2018

On 18/12/18 13:21, H. Nikolaus Schaller wrote:

> Now the driver becomes enabled, sends DCS commands to the panel and
> receives register values.

I have a DSI video mode panel that attaches to OMAP5 uevm (I think you
sent it to me long time back), and I made some tests with that.

Now, oddly, I couldn't get even an old branch working with that, and I
thought it should have worked fine. I get GFX underflows. But if I use
kmstest and just show a plane of 400x400, it works. So I think the DSI
side is ok, and DISPC side is mostly ok, but for some odd reason, DSS is
not able to fetch pixels fast enough.

So I tried to get to the same stage (400x400) working with latest -rc7.

> But panel still stays (almost) black and shows no image.

And I got this same issue.

> Somtimes there are errors:
> [   20.852710] DSI: omapdss DSI error: VC(0) busy when trying to
> configure it!
> [   20.852714] DSI: omapdss DSI error: VC(1) busy when trying to
> configure it!
> [   20.852718] DSI: omapdss DSI error: VC(2) busy when trying to
> configure it!
> [   20.852721] DSI: omapdss DSI error: VC(3) busy when trying to
> configure it!

I did not get these...

> On other occasions we can see a single vertical line displayed which
> appears to
> show some X11 or framebuffer content. At least it changes if we launch
> e.g. xterm
> and changes back if we stop it.

And I saw a similar single line too.

Comparing it to the (mostly) working kernel, I found out that the bus
flags are again broken. I attached a quick hack patch that seems to fix
them, and with that I get a working 400x400 plane, but underflows with
full-screen plane.

I couldn't quite figure out how to fix the bus-flags correctly, though.


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