[Intel-gfx] [PATCH 7/7] drm/i915: Allow user to set cache at BO creation

[Jordan Justen]

On 2023-04-05 00:45:24, Lionel Landwerlin wrote:
> On 04/04/2023 19:04, Yang, Fei wrote:
> >> Subject: Re: [Intel-gfx] [PATCH 7/7] drm/i915: Allow user to set cache at BO creation
> >>
> >> Just like the protected content uAPI, there is no way for userspace to tell
> >> this feature is available other than trying using it.
> >>
> >> Given the issues with protected content, is it not thing we could want to add?
> > Sorry I'm not aware of the issues with protected content, could you elaborate?
> > There was a long discussion on teams uAPI channel, could you comment there if
> > any concerns?
> >
> 
> We wanted to have a getparam to detect protected support and were told 
> to detect it by trying to create a context with it.
> 

An extensions system where the detection mechanism is "just try it",
and assume it's not supported if it fails. ??

This seem likely to get more and more problematic as a detection
mechanism as more extensions are added.

> 
> Now it appears trying to create a protected context can block for 
> several seconds.
> 
> Since we have to report capabilities to the user even before it creates 
> protected contexts, any app is at risk of blocking.
> 

This failure path is not causing any re-thinking about using this as
the extension detection mechanism?

Doesn't the ioctl# + input-struct-size + u64-extension# identify the
extension such that the kernel could indicate if it is supported or
not. (Or, perhaps return an array of the supported extensions so the
umd doesn't have to potentially make many ioctls for each extension of
interest.)

-Jordan