Porting GCN pre-1.2 parts from radeon to amdgpu kernel driver

[Sellers, Graham]

Hi Alexandre,

Yes, your understanding is correct.

Frankly, Alex or one of the other guys on the open source team would be best positioned to answer your questions as to what would specifically need to be done. However, yes, the gap we have here is in the amdgpu kernel driver. I pretty much only work on the user-mode side of things. Think "libVulkan.so" or "vulkan.dll" - the bit that applications link to. We talk to our kernel drivers through standard interfaces. It's the kernel driver that deals with a lot of the differences between different parts of hardware. amdgpu is a ground-up redesign of our kernel solution for Linux. The closed-source kernel driver that we were using in our Catalyst packages has been put out to pasture. For the amdgpu project, given the number of engineers we have, we have to make a tough decision between supporting interesting new features of new GPUs, or sticking with pretty basic support but backporting to older GPUs.

The differences in the graphics core itself between SI, CI and VI are actually pretty minimal (as far as the kernel driver is concerned, anyway). Where there are bigger differences are in things like the multimedia (video) engines, display controller, power management and so on. The radeon KMD has full support for all SI and CI (and earlier) "un-core" parts of the GPU. amdgpu has VI product support and some minimal (albeit disabled) support for CI, and basically nothing from SI.

Our user-mode Vulkan driver (and closed source OpenGL driver, for that matter) can talk to the amdgpu kernel driver, but not to the radeon kernel driver. The interfaces are quite different, and honestly, the radeon kernel interface isn't a great fit for Vulkan. We had considered trying to support radeon KMD in our Vulkan driver, but it doesn't seem practical. So, it seems that the options would be really to port the non-core support from radeon KMD into amdgpu, or somehow port the new KMD interfaces to radeon KMD, which would allow our Vulkan drivers to run on it, but seems like a bit of a backwards step.

There are other complications - such as it being frowned upon to have two kernel drivers for the same piece of hardware, so you'd need to port SI and CI stuff from radeon to amdgpu, and then somehow disable (or remove it) in the radeon KMD such that there was still only one driver for the GPU. It's non-trivial, but not insurmountable. Also, even though the code is there and working in radeon KMD, there are enough differences in the infrastructure that the ported support would need to be re-validated and all that stuff.

If you think you're up for the challenge, we'd be appreciative of the input. One of the major reasons to open our code and support open source is to encourage involvement and contributions from the community. That's why we're doing the GPUOpen initiative and we will be opening a lot more of our software in the future. Many of the guys on our open source team initially got involved by contributing to the project before we hired them. That kind of thing looks really good on a resume. :)

Graham

-----Original Message-----
From: Alexandre Demers [mailto:alexandre.f.demers at gmail.com] 
Sent: Saturday, January 16, 2016 2:45 PM
To: Deucher, Alexander; Sellers, Graham
Cc: dri-devel
Subject: Porting GCN pre-1.2 parts from radeon to amdgpu kernel driver

Hello to both of you,

I've been following the development mostly of the radeon driver for some time (with some small commits here and there as you may know). I was waiting to hear some news about the coming support of Vulkan API. And I have been wondering for sometime now if it would be a good think to have all GCN parts moved from the radeon driver to the amdgpu kernel driver (I had figured out it would be possible, but would it be of any use was still unanswered). I was also curious to know if the new Crimson software would support the radeon driver at some point.

Now, I may have had a clear answer: I just read from Phoronix' editor Michael Larabel
(http://www.phoronix.com/scan.php?page=news_item&px=Help-Bring-Older-GCN-To-AMDGPU)
that Vulkan would come to the amdgpu driver only, that the blob (which should eventually be opened) would support all GCN parts and that the only missing part to support GCN pre-1.2 parts with both Vulkan and Crimson would be to have them ported from the radeon driver to the amdgpu driver. Am I understanding correctly?

I'd be interested to know a bit more about the task and I may try to start the work or join someone who would already be interested in doing so.

Any comments on the matter? Any missunderstood thing?

Cheers!

--
Alexandre Demers