[Intel-gfx] RFC: pipe writeback design for i915

[Ville Syrjälä]

On Fri, Jan 31, 2020 at 12:55:45PM +0200, Jani Nikula wrote:
> On Fri, 31 Jan 2020, "Bharadiya,Pankaj" <pankaj.laxminarayan.bharadiya at intel.com> wrote:
> > I am exploring the way of implementing the pipe writeback feature in i915 and
> > would like to get early feedback on design.
> >
> > We have a Wireless display(WD) transcoder which can be used for capturing
> > display pipe output to memory. It is generally intended for wireless display,
> > but can be used for other functions such as in validation automation where crc
> > based comparison is not feasible.
> 
> I think you should probably explore the use case and driver/igt impact
> further before embarking on the implementation.
> 
> - How much do you need to modify existing code in kernel and igt to make
>   use of writeback connectors?
> 
> - What kind of test coverage do you get? Pipe CRC is used in connection
>   with the physical encoders. In contrast, you won't have that with WD
>   transcoders. (Design wise I think this may mean you'll also need
>   "writeback encoders", instead of trying to plug it into existing
>   encoders.) So you'll only test the pipe side of things, which roughly
>   corresponds to pipe CRC coverage I guess. I guess it could speed up
>   that part of testing because you can then skip the physical
>   connectors, but you do have to test them also. So it's not a panacea.

The main benefit I'm looking forward to is for reverse engineering.
As in answwering the age old question: "let me see wtf the hw is
actually doing to my pixels?". I want this!

-- 
Ville Syrjälä
Intel
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