Re: [Xen-devel] Xen ARM GPU passthrough without IOMMU

[Andrii Anisov <andrii.anisov@xxxxxxxxx>]

Hello Jinch,

On 05.03.19 15:35, Jinch wrote:
> Thank you for your reply,
> Now I can set the disk and some basic devices to run Android domu to console,
> The main issue is the display GUI of Android.
Here you should distinguish clearly display subsystem and 3D rendering engine. 
Yet you need them both for your Android showing you something.
We have a quite generic PV DRM implementation, both FE and BE, which is called 
to serve as a display subsystem.
But 3D rendering is really vendor specific, and no generic approach 
implementation is known to me. Except software rendering for sure:)

You  might look at the hwcomposer we are using in our setup [1], but it is 
still IMG specific in terms of 3D.

> I can use the drm PV drivers at https://github.com/xen-troops/displ_be to set 
> the drm driver,
> Or the next step is to research how to set drm device passthrough.
Sorry I didn't get that clearly. Do you say that you managed to bringup PV DRM 
for Android? Or it is your next step? And why do you say about DRM passthrough?

> But the imxqxp board I use doesn’t have IOMMU, the GPU passthrough may have 
> some problems.
I guess you should ask your GPU vendor about their virtualization solution 
first. That might give you a clue how can you provide your GPU access to other 
VM address space.
On our side we requested hypervisor to translate IPA to PA [2], and then fed 
those addresses to GPU from its driver. We do that for buggy silicon revision 
where GPU's IOMMU does not work.
Yet it makes more boards available for development, rather than for production.

> Do you have some tutorials about how to set display and GUI when running 
> Android as domu?
You might grab more information about PV DRM here [3].
XEN vdispl configuration you will find here [4].
Setting up Android display and GUI - you will not find any tutorials. You need 
your hwcomposer and gralloc which are 3D vendor specific, so contact your 
vendor.

[1] 
https://github.com/xen-troops/android_external_drm_hwcomposer/commits/android-9.0.0_r3-xt0.2
[2] https://github.com/xen-troops/xen/blob/master/xen/arch/arm/mm.c#L1332
[3] https://lwn.net/Articles/750258/
[4] https://xenbits.xen.org/docs/unstable-staging/man/xl.cfg.5.html#Devices

--
Sincerely,
Andrii Anisov.

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