Re: Feature Request: Ability to decode bus/dma address back into physical address

[Jerome Glisse <j.glisse-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>]

On Wed, Aug 02, 2017 at 07:05:11PM +0200, Christian König wrote:
> Am 02.08.2017 um 18:43 schrieb Jerome Glisse:
> > On Wed, Aug 02, 2017 at 10:26:40AM +0200, Christian König wrote:
> > > [SNIP]
> > So to summarize you are saying you do not trust the value you get from
> > pci_map_page() ?
> 
> Well, what we don't trust is that we actually get this value correctly into
> our page tables.
> 
> > If not then i stress again that you have all the informations you need
> > inside the amdgpu driver. You can take the same scheme i propose to
> > dump ttm.dma_address[] and compare against content of GPU page table.
> 
> Yes, exactly. But then again we have the mapping page to dma-address
> (because that is what drivers usually need), but what we need for debugging
> is a map with the info dma-address to page.

Why would you need the reverse ? You have a GPU virtual address do the following:
GPU vaddr -> GPU page table entrie -> bus address
GPU vaddr -> bo_va_mapping -> bo_va -> bo -> page -> dma/bus address

Compage the 2 values if they are the same then the GPU is looking where
you wanted it to look. If they are different then you know you have a bug
knowing the physical page addres do not give you any more informations
here ?

Jérôme