On 2022-11-30 19:59, Mikhail Krylov wrote:
On Wed, Nov 30, 2022 at 11:07:32AM -0500, Alex Deucher wrote:
On Wed, Nov 30, 2022 at 10:42 AM Robin Murphy <robin.mur...@arm.com> wrote:

On 2022-11-30 14:28, Alex Deucher wrote:
On Wed, Nov 30, 2022 at 7:54 AM Robin Murphy <robin.mur...@arm.com> wrote:

On 2022-11-29 17:11, Mikhail Krylov wrote:
On Tue, Nov 29, 2022 at 11:05:28AM -0500, Alex Deucher wrote:
On Tue, Nov 29, 2022 at 10:59 AM Mikhail Krylov <sqar...@gmail.com> wrote:

On Tue, Nov 29, 2022 at 09:44:19AM -0500, Alex Deucher wrote:
On Mon, Nov 28, 2022 at 3:48 PM Mikhail Krylov <sqar...@gmail.com> wrote:

On Mon, Nov 28, 2022 at 09:50:50AM -0500, Alex Deucher wrote:

[excessive quoting removed]

So, is there any progress on this issue? I do understand it's not a high
priority one, and today I've checked it on 6.0 kernel, and
unfortunately, it still persists...

I'm considering writing a patch that will allow user to override
need_dma32/dma_bits setting with a module parameter. I'll have some time
after the New Year for that.

Is it at all possible that such a patch will be merged into kernel?

On Mon, Nov 28, 2022 at 9:31 AM Mikhail Krylov <sqar...@gmail.com> wrote:
Unless someone familiar with HIMEM can figure out what is going wrong
we should just revert the patch.


Okay, I was suggesting that mostly because

a) it works for me with dma_bits = 40 (I understand that's what it is
without the original patch applied);

b) there's a hint of uncertainity on this line
saying that for AGP dma_bits = 32 is the safest option, so apparently there are
setups, unlike mine, where dma_bits = 32 is better than 40.

But I'm in no position to argue, just wanted to make myself clear.
I'm okay with rebuilding the kernel for my machine until the original
patch is reverted or any other fix is applied.

What GPU do you have and is it AGP?  If it is AGP, does setting
radeon.agpmode=-1 also fix it?


That is ATI Radeon X1950, and, unfortunately, radeon.agpmode=-1 doesn't
help, it just makes 3D acceleration in games such as OpenArena stop

Just to confirm, is the board AGP or PCIe?


It is AGP. That's an old machine.

Can you check whether dma_addressing_limited() is actually returning the
expected result at the point of radeon_ttm_init()? Disabling highmem is
presumably just hiding whatever problem exists, by throwing away all
   >32-bit RAM such that use_dma32 doesn't matter.

The device in question only supports a 32 bit DMA mask so
dma_addressing_limited() should return true.  Bounce buffers are not
really usable on GPUs because they map so much memory.  If
dma_addressing_limited() returns false, that would explain it.

Right, it appears to be the only part of the offending commit that
*could* reasonably make any difference, so I'm primarily wondering if
dma_get_required_mask() somehow gets confused.


Can you see that dma_addressing_limited() and dma_get_required_mask()
return in this case?



Unfortunately, right now I don't have enough time for kernel
modifications and rebuilds (I will later!), so I did a quick-and-dirty
research with kprobe.

The problem is that dma_addressing_limited() seems to be inlined and
kprobe fails to intercept it.

But I managed to get the result of dma_get_required_mask(). It returns
0x7fffffff (!) on the vanilla (with the patch, buggy) kernel:
$ sudo kprobe-perf 'r:dma_get_required_mask $retval'
Tracing kprobe dma_get_required_mask. Ctrl-C to end.
         modprobe-1244    [000] d...   105.582816: dma_get_required_mask: 
(radeon_ttm_init+0x61/0x240 [radeon] <- dma_get_required_mask) arg1=0x7fffffff

This function does not even get called in the kernel without the patch
that I built myself. I believe that's because ttm_bo_device_init()
doesn't call it without the patch.

Hope that helps at least a bit. If not, I'll be able to do more thorough
research in a couple of weeks, probably.

Hmm, just to clarify, what's your actual RAM layout? I've been assuming
that the issue must be caused by unexpected DMA address truncation, but
double-checking the older threads it seems that might not be the case.
I just did a quick sanity-check of both HIGHMEM4G and HIGHMEM64G configs
in a VM with either 2GB or 4GB of RAM assigned, and the
dma_direct_get_required_mask() calculation seemed to return the
appropriate result for all combinations.

Otherwise, the only significant difference of use_dma32 seems to be to
switch TTM's allocation flags from GFP_HIGHUSER to GFP_DMA32. Could it
just be that the highmem support somewhere between TTM and radeon has
bitrotted, and it hasn't been noticed until this change because everyone
still using a 32-bit system with highmem also happens not to be using a
newer 40-bit-capable GPU? Or perhaps it never worked for AGP at all, in
which case an explicit special case might be clearer?

diff --git a/drivers/gpu/drm/radeon/radeon_ttm.c 
index d33fec488713..acb2d534bff5 100644
--- a/drivers/gpu/drm/radeon/radeon_ttm.c
+++ b/drivers/gpu/drm/radeon/radeon_ttm.c
@@ -696,6 +696,7 @@ int radeon_ttm_init(struct radeon_device *rdev)
+                              rdev->flags & RADEON_IS_AGP ||
        if (r) {
                DRM_ERROR("failed initializing buffer object driver(%d).\n", r);

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