linux-kernel - Re: [PATCH 00/83] AMD HSA kernel driver

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Date:	Sun, 13 Jul 2014 11:42:58 +0200
From:	Daniel Vetter <daniel@...ll.ch>
To:	Jerome Glisse <j.glisse@...il.com>
Cc:	Christian König <christian.koenig@....com>,
	"Gabbay, Oded" <Oded.Gabbay@....com>,
	"oded.gabbay@...il.com" <oded.gabbay@...il.com>,
	"Lewycky, Andrew" <Andrew.Lewycky@....com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
	"Deucher, Alexander" <Alexander.Deucher@....com>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	Jesse Barnes <jbarnes@...tuousgeek.org>
Subject: Re: [PATCH 00/83] AMD HSA kernel driver

On Sat, Jul 12, 2014 at 6:49 PM, Jerome Glisse <j.glisse@...il.com> wrote:
>> Hm, so the hsa part is a completely new driver/subsystem, not just an
>> additional ioctl tacked onto radoen? The history of drm is littered with
>> "generic" ioctls that turned out to be useful for exactly one driver.
>> Which is why _all_ the command submission is now done with driver-private
>> ioctls.
>>
>> I'd be quite a bit surprised if that suddenly works differently, so before
>> we bless a generic hsa interface I really want to see some implementation
>> from a different vendor (i.e. nvdidia or intel) using the same ioctls.
>> Otherwise we just repeat history and I'm not terribly inclined to keep on
>> cleanup up cruft forever - one drm legacy is enough ;-)
>>
>> Jesse is the guy from our side to talk to about this.
>> -Daniel
>
> I am not worried about that side, the hsa foundation has pretty strict
> guidelines on what is hsa compliant hardware ie the hw needs to understand
> the pm4 packet format of radeon (well small subset of it). But of course
> this require hsa compliant hardware and from member i am guessing ARM Mali,
> ImgTech, Qualcomm, ... so unless Intel and NVidia joins hsa you will not
> see it for those hardware.
>
> So yes for once same ioctl would apply to different hardware. The only things
> that is different is the shader isa. The hsafoundation site has some pdf
> explaining all that but someone thought that slideshare would be a good idea
> personnaly i would not register to any of the website just to get the pdf.
>
> So to sumup i am ok with having a new device file that present uniform set
> of ioctl. It would actualy be lot easier for userspace, just open this fix
> device file and ask for list of compliant hardware.
>
> Then radeon kernel driver would register itself as a provider. So all ioctl
> decoding marshalling would be share which makes sense.

There's also the other side namely that preparing the cp ring in
userspace and submitting the entire pile through a doorbell to the hw
scheduler isn't really hsa exclusive. And for a solid platform with
seamless gpu/cpu integration that means we need standard ways to set
gpu context priorities and get at useful stats like gpu time used by a
given context.

To get there I guess intel/nvidia need to reuse the hsa subsystem with
the command submission adjusted a bit. Kinda like drm where kms and
buffer sharing is common and cs driver specific.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch
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