linux-kernel - Re: [PATCH 06/11] ttm/driver: Expand ttm_backend_func to include two overrides for TTM page pool.

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Message-ID: <20111024181806.GA4369@phenom.dumpdata.com>
Date:	Mon, 24 Oct 2011 14:18:06 -0400
From:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To:	Thomas Hellstrom <thomas@...pmail.org>
Cc:	linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org,
	thellstrom@...are.com, airlied@...hat.com,
	xen-devel@...ts.xensource.com, j.glisse@...hat.com,
	bskeggs@...hat.com
Subject: Re: [PATCH 06/11] ttm/driver: Expand ttm_backend_func to include two
 overrides for TTM page pool.

> >For that there are couple of architectural issues I am not sure how to solve.
> >
> >There has to be some form of TTM<->[Radeon|Nouveau] lookup mechanism
> >to say: "here is a 'struct page *', give me the bus address". Currently
> >this is solved by keeping an array of DMA addresses along with the list
> >of pages. And passing the list and DMA address up the stack (and down)
> >from TTM up to the driver (when ttm->be->func->populate is called and they
> >are handed off) does it. It does not break any API layering .. and the internal
> >TTM pool (non-DMA) can just ignore the dma_address altogether (see patch above).
> >
> 
> I actually had something more simple in mind, but when tinking a bit
> deeper into it, it seems more complicated than I initially thought.
> 
> Namely that when we allocate pages from the ttm_backend, we actually
> populated it at the same time. be::populate would then not take a
> page array as an argument, and would actually be a no-op on many
> drivers.

The programming of the gfx's MMU.. would be done via a new API call?
I think this needs a bit of whiteboarding for me to be sure I understand you.
> 
> This makes us move towards struct ttm_tt consisting almost only of
> its backend, so that whole API should perhaps be looked at with new
> eyes.
> 
> So anyway, I'm fine with high level things as they are now, and the

Great!
> dma_addr issue can be looked at at a later time. If we could get a
> couple of extra eyes to review the code for style etc. would be

Anybody in particular you can recommend that I can pester^H^H^H^H politely
ask :-)

> great, because I have very little time the next couple of weeks.

<nods> Understood. 
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