Screen corruption using radeon kernel driver

[Alex Deucher]

On Wed, Nov 30, 2022 at 7:54 AM Robin Murphy <robin.murphy at 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 <sqarert at 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 <sqarert at 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 <sqarert at gmail.com> wrote:
> >>>>>> Unless someone familiar with HIMEM can figure out what is going wrong
> >>>>>> we should just revert the patch.
> >>>>>>
> >>>>>> Alex
> >>>>>
> >>>>>
> >>>>> 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
> >>>>> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/gpu/drm/radeon/radeon_device.c#n1359
> >>>>> 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?
> >>>>
> >>>> Alex
> >>>
> >>> That is ATI Radeon X1950, and, unfortunately, radeon.agpmode=-1 doesn't
> >>> help, it just makes 3D acceleration in games such as OpenArena stop
> >>> working.
> >>
> >> Just to confirm, is the board AGP or PCIe?
> >>
> >> Alex
> >
> > 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.

Alex