Re: [RFC] i915: make the probe asynchronous

[Takashi Iwai <tiwai@suse.de>]

On Tue, 14 Aug 2018 11:34:07 +0200,
Daniel Vetter wrote:
> 
> On Tue, Aug 14, 2018 at 02:54:31PM +0800, Feng Tang wrote:
> > Hi Jani, Daniel
> > 
> > Could you help to comment? thanks,
> > 
> > - Feng
> > 
> > On Thu, Jul 12, 2018 at 03:51:34PM +0800, Feng Tang wrote:
> > > 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 :(
> 
> Sorry this wa all irc discussions around the hdcp2 patches from
> Ramalingam. There's hacks in his latest patch series to work around the
> audio issues.
> 
> > > > 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.
> 
> Erm, the entire point of this discussion was the request_module() doesn't
> work. request_module() does _not_ make dependencies explicit at all.

FYI, the upcoming 4.19 will have the completion in audio side binding,
so this problem should be solved there.


thanks,

Takashi
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