linux-kernel - Re: refactor the i915 GVT support

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Date:   Thu, 26 Aug 2021 14:08:09 +0800
From:   Zhenyu Wang <zhenyuw@...ux.intel.com>
To:     Christoph Hellwig <hch@....de>
Cc:     Jason Gunthorpe <jgg@...dia.com>,
        "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
        Greg KH <gregkh@...uxfoundation.org>,
        "intel-gfx@...ts.freedesktop.org" <intel-gfx@...ts.freedesktop.org>,
        Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Jani Nikula <jani.nikula@...ux.intel.com>,
        Gerd Hoffmann <kraxel@...hat.com>,
        "Vivi, Rodrigo" <rodrigo.vivi@...el.com>,
        "intel-gvt-dev@...ts.freedesktop.org" 
        <intel-gvt-dev@...ts.freedesktop.org>,
        "Wang, Zhi A" <zhi.a.wang@...el.com>,
        Jani Nikula <jani.nikula@...el.com>,
        Luis Chamberlain <mcgrof@...nel.org>
Subject: Re: refactor the i915 GVT support

On 2021.08.20 16:17:24 +0200, Christoph Hellwig wrote:
> On Thu, Aug 19, 2021 at 04:29:29PM +0800, Zhenyu Wang wrote:
> > I'm working on below patch to resolve this. But I met a weird issue in
> > case when building i915 as module and also kvmgt module, it caused
> > busy wait on request_module("kvmgt") when boot, it doesn't happen if
> > building i915 into kernel. I'm not sure what could be the reason?
> 
> Luis, do you know if there is a problem with a request_module from
> a driver ->probe routine that is probably called by a module_init
> function itself?
> 
> In the meantime I'll try to reproduce it locally, but I always had a
> hard time getting useful results out of a modular i915, especially
> when combined with module paramters. (no blame on i915, just the problem
> with modules needed early on).
> 
> > 
> > > But the problem I see is that after moving gvt device model (gvt/*.c
> > > except kvmgt.c) into kvmgt module, we'll have issue with initial mmio
> > > state which current gvt relies on, that is in design supposed to get
> > > initial HW state before i915 driver has taken any operation.  Before
> > > we can ensure that, I think we may only remove MPT part first but
> > > still keep gvt device model as part of i915 with config. I'll try to
> > > split that out.
> > 
> > Sorry I misread the code that as we always request kvmgt module when
> > gvt init, so it should still apply original method that this isn't a
> > problem. Our current validation result has shown no regression as well.
> 
> What does initial mmio state mean?  This is something new to me.  But
> as you said in this mail unless I missed something very big it should
> work the same as before.
>

It's gvt internal track for all gfx mmio state, and yes with your current
change it should still work as before.

> > -static inline void intel_context_unpin(struct intel_context *ce)
> > +static inline void _intel_context_unpin(struct intel_context *ce)
> >  {
> >  	if (!ce->ops->sched_disable) {
> >  		__intel_context_do_unpin(ce, 1);
> > @@ -150,6 +150,7 @@ static inline void intel_context_unpin(struct intel_context *ce)
> >  		}
> >  	}
> >  }
> > +void intel_context_unpin(struct intel_context *ce);
> 
> Looking at intel_context_unpin/_intel_context_unpin is there really
> a need to have this inline to start with?  It don't see much the compiler
> could optimize by inlining it.

I'll send patch to i915 for this, and get more comments there.

thanks

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