[PATCH] drm/amdgpu:implement CONTEXT_CONTROL (v3)

[Christian König]

> 1) Is that my patch must work with current MESA driver ? (even MESA doesn't change any bit of its logic) ?
Yes and it must work with all old versions of Mesa. This is usual the 
tricky part to get right and most of my concern right now.

> 2) is that my patch can let kmd go to a new path (using CONTEXT_CONTROL) with bump up the KMS version ?
No, not necessary. Bumping the KMS version can only be used to signal to 
Mesa that it can use a new feature. E.g. Mesa can then stop to use 
CONTEXT_CONTROL in it's IBs, but there isn't any guarantee that it does.

> 3) will MESA change its logic (align with close OGL driver) and bump up its version so that new version MESA can work with new version KMS/kmd?
No, usually Mesa is changed in a way so that it works with both old and 
new kernel drivers. Only when there is a really good reason (usually 
critical bugs in the kernel driver) Mesa will drop support for older 
kernel versions.

As I said in my internal mail let's do it like this:

1. Don't touch the preamble flag at all, just keep that handling as it 
is for now.

2. Add the CONTEXT_CONTROL with the appropriate handling on context 
switch and bump the version number to signal that this is done.

3. When #2 is upstream we hack on Mesa to drop the CONTEXT_CONTROL 
packets from it's IBs when it sees the new kernel version.

4. When we release SR-IOV we add some logic to the kernel driver to 
ignore the preamble flag.

Regards,
Christian.

Am 06.09.2016 um 11:28 schrieb Liu, Monk:
> Hi Bas & Christian
>
> I'm not familiar with the policy of upstream kernel driver, so I cannot say if your proposal is doable or not,
>
> I have questions:
>
> 1) Is that my patch must work with current MESA driver ? (even MESA doesn't change any bit of its logic) ?
> 2) is that my patch can let kmd go to a new path (using CONTEXT_CONTROL) with bump up the KMS version ?
> 3) will MESA change its logic (align with close OGL driver) and bump up its version so that new version MESA can work with new version KMS/kmd?
>
> With above question addressed, we can together discuss how to modify CONTEXT_CONTROL patch
>
> BR Monk
>
>
>
>
> -----Original Message-----
> From: Koenig, Christian
> Sent: Monday, September 05, 2016 7:57 PM
> To: Liu, Monk <Monk.Liu at amd.com>
> Cc: brahma_hybrid_dev <brahma_hybrid_dev at amd.com>
> Subject: Re: [PATCH] drm/amdgpu:implement CONTEXT_CONTROL (v3)
>
> Another possible solution which just came to my mind: Completely ignore the preamble flag on the IB on keep the existing preamble handling as it is.
>
> Just insert a CONTEXT_CONTROL package at the beginning of the command submission controlled by if we have seen a context switch or not and then raise the driver version number.
>
> Then we can fix Mesa to not emit the CONTEXT_CONTROL commands from the UMD any more and when SR-IOV comes out we add a handling to ignore the preamble flag in the kernel when it is activated.
>
> Does that sounds like it should work?
>
> Regards,
> Christian.
>
>
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