DRM_UDL and GPU under Xserver

Thu Apr 5 06:44:21 PDT 2018

On Thu, Apr 05, 2018 at 11:10:03AM +0000, Alexey Brodkin wrote:
> Hi Daniel, Lucas,
> 
> On Thu, 2018-04-05 at 12:59 +0200, Daniel Vetter wrote:
> > On Thu, Apr 5, 2018 at 12:29 PM, Lucas Stach <l.stach at pengutronix.de> wrote:
> > > Am Donnerstag, den 05.04.2018, 11:32 +0200 schrieb Daniel Vetter:
> > > > On Thu, Apr 5, 2018 at 9:16 AM, Alexey Brodkin
> > > > <Alexey.Brodkin at synopsys.com> wrote:
> > > > > Hi Daniel,
> > > > > 
> > > > > On Thu, 2018-04-05 at 08:18 +0200, Daniel Vetter wrote:
> > > > > > On Wed, Apr 4, 2018 at 10:06 PM, Alexey Brodkin
> > > > > > <Alexey.Brodkin at synopsys.com> wrote:
> > > > > > > Hello,
> > > > > > > 
> > > > > > > We're trying to use DisplayLink USB2-to-HDMI adapter to render
> > > > > > > GPU-accelerated graphics.
> > > > > > > Hardware setup is as simple as a devboard + DisplayLink
> > > > > > > adapter.
> > > > > > > Devboards we use for this experiment are:
> > > > > > >  * Wandboard Quad (based on IMX6 SoC with Vivante GPU) or
> > > > > > >  * HSDK (based on Synopsys ARC HS38 SoC with Vivante GPU as
> > > > > > > well)
> > > > > > > 
> > > > > > > I'm sure any other board with DRM supported GPU will work,
> > > > > > > those we just used
> > > > > > > as the very recent Linux kernels could be easily run on them
> > > > > > > both.
> > > > > > > 
> > > > > > > Basically the problem is UDL needs to be explicitly notified
> > > > > > > about new data
> > > > > > > to be rendered on the screen compared to typical bit-streamers
> > > > > > > that infinitely
> > > > > > > scan a dedicated buffer in memory.
> > > > > > > 
> > > > > > > In case of UDL there're just 2 ways for this notification:
> > > > > > >  1) DRM_IOCTL_MODE_PAGE_FLIP that calls drm_crtc_funcs-
> > > > > > > > page_flip()
> > > > > > > 
> > > > > > >  2) DRM_IOCTL_MODE_DIRTYFB that calls drm_framebuffer_funcs-
> > > > > > > > dirty()
> > > > > > > 
> > > > > > > But neither of IOCTLs happen when we run Xserver with xf86-
> > > > > > > video-armada driver
> > > > > > > (see https://urldefense.proofpoint.com/v2/url?u=http-3A__git.ar
> > > > > > > m.linux.org.uk_cgit_xf86-2Dvideo-2Darmada.git_log_-3Fh-
> > > > > > > 3Dunstable-2Ddevel&d=DwIBaQ&;
> > > > > > > c=DPL6_X_6JkXFx7AXWqB0tg&r=lqdeeSSEes0GFDDl656eViXO7breS55ytWkh
> > > > > > > pk5R81I&m=oEAlP64L9vkuUs_k3kGwwwlN1WJbDMJbCo0uDhwKwwk&s=3ZHj-
> > > > > > > 6JXZBLSTWg_4KMnL0VNi7z8c0RxHzj2U5ywVIw&e=).
> > > > > > > 
> > > > > > > Is it something missing in Xserver or in UDL driver?
> > > > > > 
> > > > > > Use the -modesetting driverr for UDL, that one works correctly.
> > > > > 
> > > > > If you're talking about "modesetting" driver of Xserver [1] then
> > > > > indeed
> > > > > picture is displayed on the screen. But there I guess won't be any
> > > > > 3D acceleration.
> > > > > 
> > > > > At least that's what was suggested to me earlier here [2] by Lucas:
> > > > > ---------------------------->8---------------------------
> > > > > For 3D acceleration to work under X you need the etnaviv specific
> > > > > DDX
> > > > > driver, which can be found here:
> > > > > 
> > > > > https://urldefense.proofpoint.com/v2/url?u=http-3A__git.arm.linux.org.uk_cgit_xf86-2Dvideo-2Darmada.git_log_-3Fh-3Dunsta&d=DwIBaQ&c=DPL6_X_6Jk
> > > > > XFx7AXWqB0tg&r=lqdeeSSEes0GFDDl656eViXO7breS55ytWkhpk5R81I&m=FleDFAQb2lBcZk5DMld7qpeSrB5Srsb4XPQecA5BPvU&s=YUzMQWe3lpC_pjGqRjb4MvRYh16ZBbealqf
> > > > > rywlqjKE&e=
> > > > > ble-devel
> > > > 
> > > > You definitely want to use -modesetting for UDL. And I thought with
> > > > glamour and the corresponding mesa work you should also get
> > > > accelaration. Insisting that you must use a driver-specific ddx is
> > > > broken, the world doesn't work like that anymore.
> > > 
> > > On etnaviv the world definitely still works like this. The etnaviv DDX
> > > uses the dedicated 2D hardware of the Vivante GPUs, which is much
> > > faster and efficient than going through Glamor.
> > > Especially since almost all X accel operations are done on linear
> > > buffers, while the 3D GPU can only ever do tiled on both sampler and
> > > render, where some multi-pipe 3D cores can't even read the tiling they
> > > write out. So Glamor is an endless copy fest using the resolve engine
> > > on those.
> > 
> > Ah right, I've forgotten about the vivante 2d cores again.
> > 
> > > If using etnaviv with UDL is a use-case that need to be supported, one
> > > would need to port the UDL specifics from -modesetting to the -armada
> > > DDX.
> > 
> > I don't think this makes sense.
> 
> I'm not really sure it has something to do with Etnaviv in particular.
> Given UDL might be attached to any board with any GPU that would mean we'd
> need to add those "UDL specifics from -modesetting" in all xf86-video-drivers,
> right?

X server supports multiple drivers (for different devices) in parallel.
You should be using armada for the imx-drm thing, and modesetting for udl.
And through the magic of prime it should even figure out that the device

> > > > Lucas, can you pls clarify? Also, why does -armada bind against all
> > > > kms drivers, that's probaly too much.
> > > 
> > > I think that's a local modification done by Alexey. The armada driver
> > > only binds to armada and imx-drm by default.
> 
> Actually it all magically works without any modifications.
> I just start X with the following xorg.conf [1]:
> ------------------------>8--------------------------
> Section "Device"
> 	Identifier	"Driver0"
> 	Screen		0
> 	Driver		"armada"
> EndSection
> ------------------------>8--------------------------
> 
> In fact in case of "kmscube" I had to trick Mesa like that:
> ------------------------>8--------------------------
> export MESA_LOADER_DRIVER_OVERRIDE=imx-drm

Yeah this shouldn't be necessary at all.

> ------------------------>8--------------------------
> And then UDL out works perfectly fine (that's because "kmscube"
> explicitly calls drmModePageFlip()).
> 
> As for Xserver nothing special was done.
> 
> [1] http://git.arm.linux.org.uk/cgit/xf86-video-armada.git/tree/conf/xorg-sample.conf?h=unstable-devel

xorg.log is probably more interesting. No idea whether your Xorg.conf
snippet is needed for armada or not.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch