drm/bridge: Synopsys DW-HDMI bridge driver for the Ingenic JZ4780 (was Re: Specialising the Synopsys DW-HDMI bridge driver for the Ingenic JZ4780)

[Ezequiel Garcia]

On Mon, 24 Aug 2020 at 13:05, H. Nikolaus Schaller <hns at goldelico.com> wrote:
>
> Hi Ezequiel,
>
> > Am 24.08.2020 um 15:46 schrieb Ezequiel Garcia <ezequiel at vanguardiasur.com.ar>:
> >
> > On Fri, 21 Aug 2020 at 19:24, Paul Cercueil <paul at crapouillou.net> wrote:
> >>
> >>
> >>
> >> Le sam. 22 août 2020 à 0:11, Paul Boddie <paul at boddie.org.uk> a
> >> écrit :
> >>
> >> If you send clean patches, there's no reason for me not to merge them.
> >>
> >
> > I'd really like to see HDMI support on my CI20 being merged. Thank to
> > recent ingenic-drm work and thanks for Paul Boddie and Nikolaus work,
> > the patches are IMO quite clean.
>
> I have done some testing and it appears that it only works if DRM is
> compiled into the kernel. At least in my setup. If DRM and/or HDMI are made
> modules there is no video or code doesn't compile completely.
>
> We have to analyse that further.
>

Ah! That's true.

The fix is just re-organizing the code a bit. Just pushed a possible
fix for that (following the IPU handling by Paul Cercueil),
please feel free to test this:

https://gitlab.collabora.com/linux/0day/-/commits/jz4780-drm-hdmi-module-fix-v5.9-rc2

FWIW, my test setup uses mainline vanilla U-Boot v2020.07.
The kernel is loaded via TFTP. Debian mipsel is mounted via NFS
(which means dm9000 works). I'm testing with weston and modetest.

Note that enabling DRM_INGENIC_IPU will make the driver
fail to load, as the IPU is not optional (and not present on ci20.dts).
A minor thing to fix.

Cheers,
Ezequiel

> And it seems to differ significantly from what Paul has developed recently
> to make it work. It seems to be quite lucky that we have a working setup now :)
>
> > Nikolaus, Paul: Do you have plans to submit these?
>
> Yes, as soon as we are sure that it works (and when it doesn't).
>
> But thanks to your work it is now much easier to improve things, since we
> are no longer looking for a break-through but just have to avoid regressions.
>
> > If not, I'll be happy to get them out the door for review.
>
> Let it mature a little first and have it tested on more setups and rebased
> to mainline v5.9-rc2 :)
>