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

Dan Carpenter
2014-08-27T13:04:46Z

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?

221 hdmi_level = hdmi_800mV_0dB;
222
223 /* Entry 9 is for HDMI: */
224 for (i = 0; i < 2; i++) {
225 I915_WRITE(reg, ddi_translations_hdmi[hdmi_level * 2 + i]);
^^^^^^^^^^^^^^^^^^
The static checker thinks "15 * 2 + 1 = 31" so we are beyond the size
of the largest array (either 20 or 24).

226 reg += 4;
227 }
228 }

regards,
dan carpenter