[Intel-gfx] [RFC] i915: make the probe asynchronous

[Feng Tang]

Hi Daniel,

On Thu, Jul 12, 2018 at 08:54:34AM +0200, Daniel Vetter wrote:
> On Thu, Jul 12, 2018 at 09:29:01AM +0800, Feng Tang wrote:
> > On Tue, Jun 26, 2018 at 10:29:16AM +0800, Feng Tang wrote:
> > > On Mon, Jun 25, 2018 at 05:36:32PM +0200, Daniel Vetter wrote:
> >  
> > > Hi Daneil/Jani/Takashi,
> > > 
> > > When I was testing this patch from Takashi, I further checked the kernel
> > > module code, and found that: we may need NOT to add any new codes to
> > > prepare for i915's async probe feature!
> > > 
> > > Say when i915 module is being loader due to HDA's request_module() call,
> > > in the callchain, do_init_module() has such code:
> > > 
> > >     if (!mod->async_probe_requested && (current->flags & PF_USED_ASYNC))
> > >                 async_synchronize_full();
> > > 
> > > This will garantee the asynced probe is done before it returns.
> > > 
> > > I have just tested and this seems to be enough. If I am not wrong, then
> > > we can take the i915 async patch directly. What do you think?
> > 
> > Ping for comments, thanks!
> 
> Ram (who's working on the hdcp2 code) just learned the hard way that if
> i915 registration gets delayed then audio fails to load. So if you want to
> make i915 fully async, then you _must_ fix the audio load stuff.

Thanks for sharing this info, this is a real concern. I just did a quick
search of intel-gfx mail list archive, but failed to find the details :(

> 
> The above code just shows that if you're loading things with
> request_module(), then there's not actually any async probing going on.
> Which kinda defeats the point.
> 
> So yeah, I still think we need to fix this properly, or it's pointless.

Agree, this has to be fixed. Can we just do as the hdac_i915.c to explicitly
claim this dependency by using the similar request_module("i915"), as there
may be similar dependency on i915 in the future.

Thanks,
Feng