DRM_UDL and GPU under Xserver

From: daniel@ffwll.ch (Daniel Vetter)
To: linux-snps-arc@lists.infradead.org
Subject: DRM_UDL and GPU under Xserver
Date: Mon, 9 Apr 2018 11:17:06 +0200	[thread overview]
Message-ID: <20180409091706.GU31310@phenom.ffwll.local> (raw)
In-Reply-To: <1523264135.5268.14.camel@synopsys.com>

On Mon, Apr 09, 2018@08:55:36AM +0000, Alexey Brodkin wrote:
> Hi Daniel,
> 
> On Mon, 2018-04-09@10:31 +0200, Daniel Vetter wrote:
> > On Thu, Apr 05, 2018@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.

Just enable all the drivers you have for your hw, and it should work.
Hacking on drivers without knowing what they expect tends to not work so
well.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch