Re: [PATCH] drm/i915: Protect against wrong reg offset and warn.

[Rodrigo Vivi <rodrigo.vivi@intel.com>]

On Tue, Sep 11, 2018 at 01:39:53PM -0700, Paulo Zanoni wrote:
> Em Dom, 2018-09-02 às 22:15 -0700, Rodrigo Vivi escreveu:
> > In case we forget to change intel_port_is_tc
> > we would be trying to access registers with port == -1,
> > i.e. PORT_TC_NONE, what would be wrong offset.
> > 
> 
> There are some many things that would break if intel_port_is_tc() is
> incorrect that we would have to add a few dozen more WARNs. Why add
> this specific check at this specific case and not all other checks in
> other possible cases that could break?

because static analyzer tools just bother to inform us about this
case here...

but I can mark that as intentional/false-positive/impossible/don't-bother-anymore
and just move one if you think this is really un impossible possibility

> 
> 
> > So let's just add a protection and warn here.
> > 
> > Cc: Paulo Zanoni <paulo.r.zanoni@intel.com>
> > Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
> > ---
> >  drivers/gpu/drm/i915/intel_dp.c | 3 +++
> >  1 file changed, 3 insertions(+)
> > 
> > diff --git a/drivers/gpu/drm/i915/intel_dp.c
> > b/drivers/gpu/drm/i915/intel_dp.c
> > index 436c22de33b6..6a93fa9bbbd9 100644
> > --- a/drivers/gpu/drm/i915/intel_dp.c
> > +++ b/drivers/gpu/drm/i915/intel_dp.c
> > @@ -4886,6 +4886,9 @@ static bool icl_tc_port_connected(struct
> > drm_i915_private *dev_priv,
> >  	bool is_legacy, is_typec, is_tbt;
> >  	u32 dpsp;
> >  
> > +	if (WARN_ON(tc_port == PORT_TC_NONE))
> > +		return false;
> > +
> >  	is_legacy = I915_READ(SDEISR) & SDE_TC_HOTPLUG_ICP(tc_port);
> >  
> >  	/*
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