[Intel-gfx] [PATCH] drm/i915: Don't try to handle GuC when GuC is not supported.

[Vivi, Rodrigo]

On Wed, 2016-09-21 at 18:00 -0300, Paulo Zanoni wrote:
> Em Qua, 2016-09-21 às 11:22 -0700, Rodrigo Vivi escreveu:
> > Avoid any kind of GuC handling if GuC is not supported
> > on a giving platform.
> > 
> > Besides being useless handling, our driver needs
> > to be smarter than the user trying to use an invalid paramenter.
> 
> So the problem is when a platform doesn't support guc and the user
> passes i915.enable_guc_something=1, right?

1 is not a problem actually since it means "use if available". There is
not firmware and execution continues.

2 is the problem because it means "use guc or fail if not available".
But platforms that don't have guc can't fail. driver needs to be smarter
than that.

> 
> > 
> > Cc: Jani Nikula <jani.nikula at intel.com>
> > Cc: Anusha Srivatsa <anusha.srivatsa at intel.com>
> > Cc: Christophe Prigent <christophe.prigent at intel.com>
> > Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=97573
> > Signed-off-by: Rodrigo Vivi <rodrigo.vivi at intel.com>
> > ---
> >  drivers/gpu/drm/i915/intel_guc_loader.c | 7 +++++++
> >  1 file changed, 7 insertions(+)
> > 
> > diff --git a/drivers/gpu/drm/i915/intel_guc_loader.c
> > b/drivers/gpu/drm/i915/intel_guc_loader.c
> > index 6fd39ef..da0f5ed 100644
> > --- a/drivers/gpu/drm/i915/intel_guc_loader.c
> > +++ b/drivers/gpu/drm/i915/intel_guc_loader.c
> > @@ -720,6 +720,13 @@ void intel_guc_init(struct drm_device *dev)
> >  	struct intel_guc_fw *guc_fw = &dev_priv->guc.guc_fw;
> >  	const char *fw_path;
> >  
> > +	if (!HAS_GUC(dev)) {
> > +		i915.enable_guc_loading = 0;
> > +		i915.enable_guc_submission = 0;
> > +		fw_path = NULL;
> > +		return;
> > +	}
> 
> Instead of this, how about we just patch the code below with:
> 
> if (!HAS_GUC(dev_priv)) {
> 	i915.enable_guc_loading = 0;
> 	i915.enable_guc_submission = 0;
> } else {
> 	/* A negative value means "use platform default" */
> 	if (i915.enable_guc_loading < 0)
> 		i915.enable_guc_loading = HAS_GUC_UCODE(dev_priv);
> 	if (i915.enable_guc_submission < 0)
> 		i915.enable_guc_submission = HAS_GUC_SCHED(dev_priv);
> }

yeap, this works as well. I just went for the simplest option that
minimized at most any interactions for platforms where GuC simply
doesn't exist.

> 
> Or we could even go with our current "design pattern" and create
> intel_sanitize_guc_options().

This is indeed a very good idea.

> 
> This way we'll be able to avoid adding a second failure code path,
> since we already have one for platforms with guc but options disabled.
> 
> 
> > +
> >  	/* A negative value means "use platform default" */
> >  	if (i915.enable_guc_loading < 0)
> >  		i915.enable_guc_loading = HAS_GUC_UCODE(dev);