Re: drm/i915/bdw: Provide the BDW specific HDMI buffer translation table

Damien Lespiau
2014-08-27T13:12:11Z

On Wed, Aug 27, 2014 at 04:04:46PM +0300, Dan Carpenter wrote:
> Hello Damien Lespiau,
>
> The patch a26aa8baee6c: "drm/i915/bdw: Provide the BDW specific HDMI
> buffer translation table" from Aug 1, 2014, leads to the following
> static checker warning:
>
> drivers/gpu/drm/i915/intel_ddi.c:225 intel_prepare_ddi_buffers()
> error: buffer overflow 'ddi_translations_hdmi' 24 <= 31
>
> drivers/gpu/drm/i915/intel_ddi.c
> 155 static void intel_prepare_ddi_buffers(struct drm_device *dev, enum port port)
> 156 {
> 157 struct drm_i915_private *dev_priv = dev->dev_private;
> 158 u32 reg;
> 159 int i, n_hdmi_entries, hdmi_800mV_0dB;
> 160 int hdmi_level = dev_priv->vbt.ddi_port_info[port].hdmi_level_shift;
> ^^^^^^^^^^
> The static checker thinks this is a number between 0-15. I didn't check
> if that was correct.
>
> 161 const u32 *ddi_translations_fdi;
>
> [ snip ]
>
> 186 ddi_translations_hdmi = bdw_ddi_translations_hdmi;
> 187 n_hdmi_entries = ARRAY_SIZE(bdw_ddi_translations_hdmi);
> ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
> limit is the size of the array.
>
> 188 hdmi_800mV_0dB = 7;
> 189 }
> 190
> 191 switch (port) {
> 192 case PORT_A:
> 193 ddi_translations = ddi_translations_edp;
> 194 break;
> 195 case PORT_B:
> 196 case PORT_C:
> 197 ddi_translations = ddi_translations_dp;
> 198 break;
> 199 case PORT_D:
> 200 if (intel_dp_is_edp(dev, PORT_D))
> 201 ddi_translations = ddi_translations_edp;
> 202 else
> 203 ddi_translations = ddi_translations_dp;
> 204 break;
> 205 case PORT_E:
> 206 ddi_translations = ddi_translations_fdi;
> 207 break;
> 208 default:
> 209 BUG();
> 210 }
> 211
> 212 for (i = 0, reg = DDI_BUF_TRANS(port);
> 213 i < ARRAY_SIZE(hsw_ddi_translations_fdi); i++) {
> 214 I915_WRITE(reg, ddi_translations[i]);
> 215 reg += 4;
> 216 }
> 217
> 218 /* Choose a good default if VBT is badly populated */
> 219 if (hdmi_level == HDMI_LEVEL_SHIFT_UNKNOWN ||
> 220 hdmi_level >= n_hdmi_entries)
> ^^^^^^^^^^^^^^
> We cap it at the size of the array which is either 20 or 24. The static
> checker thinks it's already capped at 15 so this is not a problem.
>
> Should this be n_hdmi_entries / 2 or something? Maybe a - 1 in there?

Indeed, n_hdmi_entries needed to be:

n_hdmi_entries = ARRAY_SIZE(bdw_ddi_translations_hdmi) / 2;

This was fixed by:

commit d6699dd3a7f696a80a5f8e5bb6ecf6ff6dd7c998
Author: Damien Lespiau <damien.lespiau@intel.com>
Date: Sat Aug 9 16:29:31 2014 +0100

drm/i915: Fix wrong number of HDMI translation entries

--
Damien