On 2020-12-17 10:25, Christian König wrote:
Am 17.12.20 um 02:07 schrieb Chen Li:
On Wed, 16 Dec 2020 22:19:11 +0800,
Christian König wrote:
Am 16.12.20 um 14:48 schrieb Chen Li:
On Wed, 16 Dec 2020 15:59:37 +0800,
Christian König wrote:
[SNIP]
Hi, Christian. I'm not sure why this change is a hack here. I cannot
see the problem and wll be grateful if you give more explainations.
__memset is supposed to work on those addresses, otherwise you can't
use the
e8860 on your arm64 system.
If __memset is supposed to work on those adresses, why this
commit(https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgithub.com%2Ftorvalds%2Flinux%2Fcommit%2Fba0b2275a6781b2f3919d931d63329b5548f6d5f&data=04%7C01%7Cchristian.koenig%40amd.com%7C4ed3c075888746b7f41408d8a22811c5%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637437640274023350%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=HhWxUaLo3WpzoV6hjV%2BG1HICaIOXwsoNpzv5tNMNg8A%3D&reserved=0)
is needed? (I also notice drm/radeon didn't take this change though)
just out of curiosity.
We generally accept those patches as cleanup in the kernel with the hope
that we can find a way to work around the userspace restrictions.
But when you also have this issue in userspace then there isn't much we
can do for you.
Replacing the the direct write in the kernel with calls to writel() or
memset_io() will fix that temporary, but you have a more general
problem here.
I cannot see what's the more general problem here :( u mean performance?
No, not performance. See standards like OpenGL, Vulkan as well as VA-API
and VDPAU require that you can mmap() device memory and execute
memset/memcpy on the memory from userspace.
If your ARM base board can't do that for some then you can't use the
hardware with that board.
If the VRAM lives in a prefetchable PCI bar then on most sane Arm-based
systems I believe it should be able to mmap() to userspace with the
Normal memory type, where unaligned accesses and such are allowed, as
opposed to the Device memory type intended for MMIO mappings, which has
more restrictions but stricter ordering guarantees.
Regardless of what happens elsewhere though, if something is mapped
*into the kernel* with ioremap(), then it is fundamentally wrong per the
kernel memory model to reference that mapping directly without using I/O
accessors. That is not specific to any individual architecture, and
Sparse should be screaming about it already. I guess in this case the
UVD code needs to pay more attention to whether radeon_bo_kmap() ends up
going via ttm_bo_ioremap() or not.
(I'm assuming the initial fault was memset() with 0 trying to perform
"DC ZVA" on a Device-type mapping from ioremap() - FYI a stacktrace on
its own without the rest of the error dump showing what actually
triggered it isn't overly useful)
Robin.
For amdgpu I suggest that we allocate the UVD message in GTT
instead of VRAM
since we don't have the hardware restriction for that on the new
generations.
Thanks, I will try to dig into deeper. But what's the "hardware
restriction" meaning here? I'm not familiar with video driver stack
and amd gpu, sorry.
On older hardware (AGP days) the buffer had to be in VRAM (MMIO)
memory, but on
modern system GTT (system memory) works as well.
IIUC, e8860 can use amdgpu(I use radeon now) beause its device id 6822
is in amdgpu's table. But I cannot tell whether e8860 has iommu, and I
cannot find iommu from lspci, so graphics translation table may not
work here?
That is not related to IOMMU. IOMMU is a feature of the CPU/motherboard.
This is implemented using GTT, e.g. the VM page tables inside the GPU.
And yes it should work I will prepare a patch for it.
BTW: How does userspace work on arm64 then? The driver stack
usually only works
if mmio can be mapped directly.
I also post two usespace issue on mesa, and you may be interested
with them:
https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgitlab.freedesktop.org%2Fmesa%2Fmesa%2F-%2Fissues%2F3954&data=04%7C01%7Cchristian.koenig%40amd.com%7C4ed3c075888746b7f41408d8a22811c5%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637437640274023350%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=ZR7pDS%2BCLUuMjCeKcMAXfHtbczt8WdUwSeLZCuHfCHw%3D&reserved=0
https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgitlab.freedesktop.org%2Fmesa%2Fmesa%2F-%2Fissues%2F3951&data=04%7C01%7Cchristian.koenig%40amd.com%7C4ed3c075888746b7f41408d8a22811c5%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637437640274033344%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=jAJo3aG2I1oIDTZXWhNgcKoKbd6tTdiAtc7vE4hJJPY%3D&reserved=0
I paste some virtual memory map in userspace there. (and the two
problems do bother me quite a long time.)
I don't really see a solution for those problems.
See it is perfectly valid for an application to memset/memcpy on
mmaped MMIO
space which comes from OpenGL or Vulkan.
So your CPU simply won't work with the hardware. We could work around
that with
a couple of hacks, but this is a pretty much general problem.
Regards,
Christian.
Thanks! Can you provid some details about these hacks? Should I post
another issue on the mail list?
Adjust the kernel and/or user space to never map VRAM to the CPU.
This violates the OpenGL/Vulkan specification in some ways. So not sure
if that will work or not.
Regards,
Christian.
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