[PATCHv2 00/56] drm/omap: Convert DSI code to use drm_mipi_dsi and drm_panel

[Laurent Pinchart]

Hi Sebastian,

On Wed, Feb 26, 2020 at 12:01:24AM +0100, Sebastian Reichel wrote:
> On Tue, Feb 25, 2020 at 07:42:37AM -0800, Tony Lindgren wrote:
> > * Sebastian Reichel <sre at kernel.org> [200225 02:29]:
> > > On Mon, Feb 24, 2020 at 04:10:11PM -0800, Tony Lindgren wrote:
> > > > BTW, I think there's also some refcount issue in general where
> > > > the omapdrm related modules cannot be unloaded any longer?
> > > 
> > > I wouldn't be too surprised. The dependencies are quite interesting
> > > at the moment with omapdss registering omapdrm and then omapdrm
> > > registers the drm_device, which references the encoders from
> > > omapdss. I think this is something to look at once Laurent's and
> > > my branch have been merged to avoid increasing the complexity.
> > > Technically it should be possible to link everything into one
> > > module.
> > 
> > Well the DSS is really DOSSI for Display Output SubSystem
> > Interconnect :) The devices on the interconnect are mostly
> > independent and ideally the toplevel dss driver would just
> > provide Linux generic resources to dispc and various output
> > drivers. So probably not a good idea to try to build it all
> > into a single module.
> 
> All the output drivers and dispc are already in a single module:
> omapdss.ko. There is omapdss-base.ko, omapdss.ko and omapdrm.ko
> module. omapdss-base.ko contains a few helpers, omapdss.ko contains
> dispc and all output encoders, omapdrm has the tiler code and
> wraps some of the custom DSS APIs to DRM APIs. I think the best
> way forward is to eliminate the custom API and use common DRM
> APIs directly. Then merge all 3 modules into one module.
> 
> In theory one could add modules for each encoder, but practically
> this only increases complexity. DRM cannnot hotplug encoders, so
> removing any module results in complete loss of DRM. Also during
> probe we need to load all modules, since something might be
> connected. So having extra modules is not really useful?

This was considered previously, but blocked (IIRC) because it introduced
circular dependencies with the omapdrm-specific display drivers in
drivers/gpu/drm/omapdrm/displays/. Once panel-dsi-cm goes away, I think
we can give it another try.

-- 
Regards,

Laurent Pinchart