Re: [PATCH] drm/i915: Fix wrong number of HDMI translation entries

[Jani Nikula <jani.nikula@linux.intel.com>]

On Sat, 09 Aug 2014, Damien Lespiau <damien.lespiau@intel.com> wrote:
> I keep telling myself that those tables aren't great because their size
> is the number of dwords we need to program and not the number of entries
> (number of dwords = number of entries * 2).
>
> And... I got it wrong when I refactored the code. Fortunately, it was
> only wrong when the VBT table (or the code parsing it) is itself
> erroneous. Long story short, it shouldn't matter, but still, there's a
> potential array overflow and random programming of the DDI translation
> tables.

Ugh I looked at the code. I think it would benefit from making the
tables have the right amount of entries, with struct { u32 hi, lo; } for
each element. I also dislike the ARRAY_SIZE(hsw_ddi_translations_fdi) in
the first loop, and magic 2 in the second. But that's for a rainy day.

Reviewed-by: Jani Nikula <jani.nikula@intel.com>

>
> Cc: Paulo Zanoni <paulo.r.zanoni@intel.com>
> Signed-off-by: Damien Lespiau <damien.lespiau@intel.com>
> ---
>  drivers/gpu/drm/i915/intel_ddi.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/intel_ddi.c b/drivers/gpu/drm/i915/intel_ddi.c
> index ca1f9a8..02d5584 100644
> --- a/drivers/gpu/drm/i915/intel_ddi.c
> +++ b/drivers/gpu/drm/i915/intel_ddi.c
> @@ -169,14 +169,14 @@ static void intel_prepare_ddi_buffers(struct drm_device *dev, enum port port)
>  		ddi_translations_dp = bdw_ddi_translations_dp;
>  		ddi_translations_edp = bdw_ddi_translations_edp;
>  		ddi_translations_hdmi = bdw_ddi_translations_hdmi;
> -		n_hdmi_entries = ARRAY_SIZE(bdw_ddi_translations_hdmi);
> +		n_hdmi_entries = ARRAY_SIZE(bdw_ddi_translations_hdmi) / 2;
>  		hdmi_800mV_0dB = 7;
>  	} else if (IS_HASWELL(dev)) {
>  		ddi_translations_fdi = hsw_ddi_translations_fdi;
>  		ddi_translations_dp = hsw_ddi_translations_dp;
>  		ddi_translations_edp = hsw_ddi_translations_dp;
>  		ddi_translations_hdmi = hsw_ddi_translations_hdmi;
> -		n_hdmi_entries = ARRAY_SIZE(hsw_ddi_translations_hdmi);
> +		n_hdmi_entries = ARRAY_SIZE(hsw_ddi_translations_hdmi) / 2;
>  		hdmi_800mV_0dB = 6;
>  	} else {
>  		WARN(1, "ddi translation table missing\n");
> @@ -184,7 +184,7 @@ static void intel_prepare_ddi_buffers(struct drm_device *dev, enum port port)
>  		ddi_translations_fdi = bdw_ddi_translations_fdi;
>  		ddi_translations_dp = bdw_ddi_translations_dp;
>  		ddi_translations_hdmi = bdw_ddi_translations_hdmi;
> -		n_hdmi_entries = ARRAY_SIZE(bdw_ddi_translations_hdmi);
> +		n_hdmi_entries = ARRAY_SIZE(bdw_ddi_translations_hdmi) / 2;
>  		hdmi_800mV_0dB = 7;
>  	}
>  
> -- 
> 1.8.3.1
>
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-- 
Jani Nikula, Intel Open Source Technology Center