Re: exynos-mixer 14450000.mixer: [drm:exynos_drm_register_dma] *ERROR* Device 14450000.mixer lacks support for IOMMU

[Krzysztof Kozlowski <krzk@kernel.org>]

On 31/10/2023 01:04, Mario Marietto wrote:
> Hello,
> 
> We are a team of linux enthusiasts who are trying to boot Xen on a
> Samsung XE303C12 Chromebook aka "snow"
> following the suggestions in the slide show presentation here:
> 
> https://www.slideshare.net/xen_com_mgr/xpds16-porting-xen-on-arm-to-a-new-soc-julien-grall-arm
> 
> This device uses an exynos5250 SOC dual core 1.7 GHz with 2 MB RAM, it is
> a Samsung armv7 chip with virtualization extensions.
> 
> In particular, we have it working fairly well both on the bare metal with
> a recent 6.1.59 Linux LTS kernel and also with a recent 5.4.257 LTS

Oh, these are old... Although there should be no noticeable changes
against v6.1.

v5.4 is not recent. It is four years old!

> kernel with KVM, the older LTS kernel version is used to test KVM because
> support for KVM on arm v7 was removed from Linux around kernel version
> 5.7. So we know we have the hypervisor mode enabled because we were able
> to use it with KVM.
> 
> For Xen, we are using the latest Debian build of Xen 4.17 for the Debian
> armhf architecture:

...

> 
> In this case,the kernel is able to use the exynos-drm kernel to start
> the fb0 device. But with Xen we get this error with exynos-drm:
> 
> devuan-bunsen kernel: [drm] Exynos DRM: using 14400000.fimd device for
> DMA mapping operations
> devuan-bunsen kernel: exynos-drm exynos-drm: bound 14400000.fimd (ops
> 0xc0d96354)
> devuan-bunsen kernel: exynos-mixer 14450000.mixer:
> [drm:exynos_drm_register_dma] *ERROR* Device 14450000.mixer lacks
> support for IOMMU

Hi Mario,

I don't test DRM on my Exynos boards, so my knowledge is limited, but
isn't this the answer?

> devuan-bunsen kernel: exynos-drm exynos-drm: failed to bind
> 14450000.mixer (ops 0xc0d97554): -22
> devuan-bunsen kernel: exynos-drm exynos-drm: adev bind failed: -22
> devuan-bunsen kernel: exynos-dp: probe of 145b0000.dp-controller
> failed with error -22

And that's the final confirmation that display did not probe successfully.

> 
> 
> Any ideas why booting the same Linux kernel that results in a working
> X.org display on the bare metal instead as dom0 on Xen would cause the
> display to remain dark, but most other basic functions would work, such
> as network, disk, and USB ? thanks.

BTW, it's usually good to Cc the maintainer as well, not only the
mailing list :). scripts/get_maintainer.pl will tell you the maintainers
of Exynos and Exynos DRM.

Best regards,
Krzysztof