Screen corruption using radeon kernel driver

[Robin Murphy]

On 2022-11-30 14:28, Alex Deucher wrote:
> 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.

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.

Thanks,
Robin.