DRM_UDL and GPU under Xserver

[Alexey Brodkin]

Hi Daniel,

On Mon, 2018-04-09 at 11:17 +0200, Daniel Vetter wrote:
> On Mon, Apr 09, 2018 at 08:55:36AM +0000, Alexey Brodkin wrote:
> > Hi Daniel,
> > 
> > On Mon, 2018-04-09 at 10:31 +0200, Daniel Vetter wrote:
> > > On Thu, Apr 05, 2018 at 06:39:41PM +0000, Alexey Brodkin wrote:
> > > > Hi Daniel, all,
> > 
> > [snip]
> > 
> > > > Ok it was quite some time ago so I forgot about that completely.
> > > > I really made one trivial change in xf86-video-armada:
> > > > ------------------------>8--------------------------
> > > > --- a/src/armada_module.c
> > > > +++ b/src/armada_module.c
> > > > @@ -26,7 +26,7 @@
> > > >  #define ARMADA_NAME            "armada"
> > > >  #define ARMADA_DRIVER_NAME     "armada"
> > > >  
> > > > -#define DRM_MODULE_NAMES       "armada-drm", "imx-drm"
> > > > +#define DRM_MODULE_NAMES       "armada-drm", "imx-drm", "udl"
> > > >  #define DRM_DEFAULT_BUS_ID     NULL
> > > > ------------------------>8--------------------------
> > > > 
> > > > Otherwise Xserver fails on start which is expected given "imx-drm" is intentionally removed.
> > 
> > Here I meant I explicitly disabled DRM_IMX in the kernel configuraion
> > so that it is not used in run-time.
> > 
> > > You need to keep imx-drm around. And then light up the udl display using
> > > prime. Afaiui it should all just work (but with maybe a few disconnected
> > > outputs from imx-drm around that you don't need, but that's not a
> > > problem).
> > 
> > And given my comment above I don't really see any difference between
> > DRM_IMX and DRM_UDL (except their HW implmentation which I guess should
> > not bother upper layers) so why do wee need to treat them differently?
> > 
> > Most probably I'm missing something but my thought was if we have
> > 2 equally well supported KMS devices we may easily swap them and still
> > have resulting setup functional.
> 
> armada is not a generic drm driver, but can only be used for armada-drm
> and imx-drm. You can't just use it with any drm device, for that you need
> a generic driver like -modesetting.

But "armada" is the name of xf86 "driver" only which then uses true DRM_ETNAVIV
kernel driver. That's why I'm a bit confused.

And from what I see DRM_ETNAVIV happily works with either DRM_xxx frame-buffer
device be it DRM_IMX or DRM_UDL.

-Alexey