[PATCH] drm/radeon: Always flush VM again on < CIK

[Christian König]

Hey guys,

I think I've figured out what the cause of the remaining issues is while 
working on the implicit sync stuff.

The issue happens when the flush is done because of a CS to the DMA ring 
and a CS to the GFX ring directly after that which depends on the DMA 
submission to be finished.

In this situation we insert semaphore command so that the GFX ring wait 
for the DMA ring to finish execution and normally don't flush on the GFX 
ring a second time (the flush should be done on the DMA ring and we 
waited for that to finish).

The problem here is that semaphores can't be executed on the PFP, so the 
PFP doesn't wait for the semaphore to be completed and happily starts 
fetching commands while the flush on the DMA ring isn't completed.

@Michel: can you give this branch a try and see if it now works for you: 
http://cgit.freedesktop.org/~deathsimple/linux/log/?h=vm-flushing

We should keep that behavior in mind should we switch to put IBs into 
normal BOs, cause when those a swapped out the synchronization won't 
wait for swapping them back in using the DMA as well.

Thanks,
Christian.

Am 12.08.2014 um 11:05 schrieb Christian König:
> Am 11.08.2014 um 17:00 schrieb Alex Deucher:
>> On Mon, Aug 11, 2014 at 4:42 AM, Michel Dänzer <michel at daenzer.net> 
>> wrote:
>>> On 08.08.2014 22:34, Alex Deucher wrote:
>>>> On Fri, Aug 8, 2014 at 9:31 AM, Alex Deucher 
>>>> <alexdeucher at gmail.com> wrote:
>>>>> On Fri, Aug 8, 2014 at 4:50 AM, Michel Dänzer <michel at daenzer.net> 
>>>>> wrote:
>>>>>> On 08.08.2014 17:44, Christian König wrote:
>>>>>>>>>> On Thu, Aug 7, 2014 at 3:59 PM, Alex Deucher 
>>>>>>>>>> <alexdeucher at gmail.com>
>>>>>>>>>> wrote:
>>>>>>>>>>> We should be using PFP as much as possible.  Does the attached
>>>>>>>>>>> patch help?
>>>>>>>> Unfortunately not.
>>>>>>> Maybe add a readback of the VM base addr pointer to make sure 
>>>>>>> that the
>>>>>>> write has really reached the SBRM?
>>>>>> I'm not sure what exactly you're thinking of, but I'm happy to 
>>>>>> test any
>>>>>> patches you guys come up with. :)
>>>>>>
>>>>> Maybe some variant of this patch?
>>>> Ignore that one.  typo.  Try this one instead.
>>> Thanks, but still no luck.
>> I'm out of ideas at the moment.  I'll apply your patch unless
>> Christian can think of anything else.
>
> Unfortunately not, so apply the patch for now.
>
> Christian.
>
>>
>> Alex
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