Re: [RFC] ttm merge ttm_backend & ttm_tt

[Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>]

> > I don't know why it was done that way, but I wrote the TTM DMA code
> > to be optimized for that (and it has the code to reverse direction - b/c
> > the testcases I used initially had the a,b,c,d,e,f order when doing get_pages
> > and put_pages) - but I can alter the code to do it in the forward fashion instead
> > of the reverse fashion.. Better yet, it removes around 70 lines of code from the
> > TTM DMA.
> 
> Order in which we put them back on the list can be easily change, either
> by use of add_tail or by iterating array from end to begining. i am not
> sure how much this can impact things.

Neither am I. I can run some perf numbers when playing tuxracer and see if there
is a disadvantage/advantage.

> 
> > Anyhow, it might be noting that in the commit description and perhaps make a bug-fix
> > for the put_pages being called in the error path instead of ttm_put_pages as a seperate
> > patch as you suggested.
> > 
> > 
> > [PATCH 6/6] drm/ttm: merge ttm_backend and ttm_tt
> > 
> > That is going to be a bit tricky. You are using the pci_map_page, which should not
> > be used if the pages have been allocated via the pci_alloc_coherent (they are already
> > mapped). Perhaps a simple check such as:
> > 
> > 	if !(ttm->be && ttm->be->func && ttm->be->func->get_pages) {
> > 		ttm->dma_address[i] = pci_map_page(dev->pdev, ...)
> > 	}
> 
> Your dma change are not suppose to be on top of that, idea is to add yet
> another callbacks populate+free_page which will do either pci map page
> or just use your code (ie use dma alloc and store dma addr into the
> array). So there is a missing piece here before adding your dma code.
> I just wanted to keep ttm_tt & ttm_backend merge as simple as possible
> without major change. Adding the populate + get_page callback sounded
> like good candidate for another patch.

<nods>

> > What base should I be looking at? Is this the base that Dave has for 3.2?
> 
> Should apply on top of linus master kernel as of yesterday.

Oh.. very very *very* fresh.