xilinx_drm and atomic modesetting

[Hyun Kwon]

Hi Jean-Francois,

As you noted, the Xilinx DRM driver in Xilinx tree is missing many mainline features including the atomic mode setting and needs some restructuring. Please feel free to send patches to Xilinx git-dev, but note that we are also developing / cleaning up the driver internally at Xilinx to upstream in near feature. While doing that, the code base may change due to heavy cleanup.

Thanks,
-hyun

> -----Original Message-----
> From: Jean-Francois Dagenais [mailto:jeff.dagenais at gmail.com]
> Sent: Tuesday, June 27, 2017 6:21 AM
> To: Hyun Kwon <hyunk at xilinx.com>; Michal Simek
> <michal.simek at xilinx.com>
> Cc: Soren Brinkmann <sorenb at xilinx.com>; git <git at xilinx.com>;
> airlied at linux.ie; dri-devel at lists.freedesktop.org
> Subject: xilinx_drm and atomic modesetting
>
> Hi guys,
>
> Note: I was a total DRM newbie at the beginning of this exercise. Now I
> would say I'm just newbie. ;)
>
> I am trying to implement our lvds panel using xilinx_drm on zynqmp. We
> are composing our pipeline starting with the xilinx-vdma, then a few logic
> parts from the ALI3 on zedboard ref design. The only configurable bits in
> this pipeline are the vdma registers at one end, then an enable GPIO and
> PWM going to the panel itself. The rest (resolution, etc.) are hard-coded at
> synthesis time.
>
> This makes things simpler, in theory.
>
> I opted to use the lvds-encoder.c (found upstream) which is actually a
> drm_bridge (!??), and the panel-lvds.c(also upstream) driver which take
> resolution and timings from dts and create a drm_panel. All I was missing is
> an encoder (xilinx_drm_encoder would not do). I created a somewhat
> dummy encoder which binds the crtc to the bridge just by being present. It
> is discovered by xilinx_drm_drv by the component subsys using the
> endpoints in dts.
>
> From what I now understand, there are two "worlds" in the DRM/KMS
> framework, legacy and atomic. From what I gather, xilinx_drm stands on
> the legacy side. Whereas the drm_bridge and drm_panel are more on the
> atomic side.
>
> I believe this is what's causing a few OOPS and exceptions here and there
> that I had to "patch" by adding "if" statements for null objects. For example,
> one is struct drm_connector_state missing on the crtc. This is used by
> atomic helpers invoked by the drm_bridge (if I remember correctly).
>
> In https://github.com/Xilinx/linux-
> xlnx/commit/d5733539adba1c509cb82bd3d4d418a3dbfbfd68 there is
> suggestion that xilinx_drm be converted to atomic modesetting.
>
> Is this work started? I would like to contribute by testing and submitting
> patches. Maybe a topic branch on github in linux-xlnx would help us out,
> and help you out as well to get the driver more polished sooner.
>
> Cheers!
> /jfd


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