[Xf86-video-armsoc] ARMSOC X11 plugin issues

[David Garbett]

The main difference between modesetting and armsoc is that armsoc
supports DRI2, and modesetting doesn't. This is what allows the GLES
driver to render to X buffers.

DRI2 enables any application to pass any X pixmap into the GLES/EGL
driver, so all buffers need to be allocated from shareable memory.
That's not the case with modesetting - other than the main framebuffer,
other allocations (for pixmaps and windows) can just be local to the X
server, so don't allocate from the DRM driver.

I've not looked at your DRM driver proposal so I can't really say why it
can't cope with the additional allocations. Though I do notice in your
armsoc patch that you don't handle scanout buffers any differently. In
many systems scanout buffers are a more scarce resource (perhaps they
need to be contiguous, or meet certain alignment restrictions).

David

> -----Original Message-----
> From: Maxime Ripard [mailto:maxime.ripard at free-electrons.com]
> Sent: 31 March 2016 09:55
> To: David Garbett; Marico Xu
> Cc: xorg-devel at lists.freedesktop.org; Boris Brezillon; Alexander Kaplan;
> Hans de Goede
> Subject: Re: ARMSOC X11 plugin issues
>
> On Wed, Mar 23, 2016 at 10:17:05PM +0100, Maxime Ripard wrote:
> > Hi David, Marico,
> >
> > I've been developping a DRM/KMS driver for the Allwinner SoCs[1],
> with
> > an additional patch to allocate GPU buffers [2]. Since those SoCs also
> > use a Mali GPU, using the armsoc X11 plugin seemed like a logical
> choice.
> >
> > I added support for the driver based on the 1.4 plugin [3], and
> > started using it, which turned out pretty well, we get something
> > displayed, GLES works, good.
> >
> > However, after testing it for a while, the first thing we noticed was
> > that some (large) buffer allocations would start to fail. Indeed, the
> > plugin seems to do a lot of rather small (and for most temporary ?)
> > buffer allocations, which eventually depletes the reserved memory
> > pool. The allocation then fails, and the application crashes.
> >
> > Then, we noticed (using xfce4, on debian jessie) that the systray
> > icons were not displayed for some reason. There's also some game
> > (alex4 [4]), that starts, runs, but the window content remains black
> > (but it remains interactive, audio plays and if we take a screenshot,
> > the content is on the image, but the screen remains black).
> >
> > The weird thing about it is that when using the X generic modesetting
> > plugin, everything starts to work. It seems to be allocating only one
> > buffer per plane, so we never have the memory allocation failures.
> > Which raises my first question: why is the armsoc plugin behaving
> > differently there?
> >
> > Then the graphics issues we were seeing are not there anymore, which
> > seems to indicate that it's related to the plugin. I'm a bit oblivious
> > to how X works exactly, and how applications interacts with it, but on
> > the ioctl side, nothing really stands out. Let me know if you need any
> > more tests or logs or anything.
>
> Anyone ?
>
> Thanks,
> Maxime
>
>
>
> --
> Maxime Ripard, Free Electrons
> Embedded Linux, Kernel and Android engineering http://free-
> electrons.com
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