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

From: Paulo Zanoni <paulo.r.zanoni@intel.com>
To: Rodrigo Vivi <rodrigo.vivi@intel.com>, intel-gfx@lists.freedesktop.org
Subject: Re: [PATCH] drm/i915: Protect against wrong reg offset and warn.
Date: Tue, 11 Sep 2018 13:39:53 -0700	[thread overview]
Message-ID: <1536698393.2638.2.camel@intel.com> (raw)
In-Reply-To: <20180903051500.10766-1-rodrigo.vivi@intel.com>

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?

> 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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