drm/i915/bios: Use the copy of the LFP data table always

Currently get_lvds_fp_timing() still returns a pointer to the original
data block rather than our copy. Let's convert the data pointer offsets
to be relative to the data block rather than the whole BDB. With that
we can make get_lvds_fp_timing() return a pointer to the copy.
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220405173410.11436-4-ville.syrjala@linux.intel.comReviewed-by: Jani Nikula <jani.nikula@intel.com>

drivers/gpu/drm/i915/display/intel_bios.c

@@ -191,6 +191,29 @@ static const struct {
 	  .min_size = sizeof(struct bdb_generic_dtd), },
 };
 
+/* make the data table offsets relative to the data block */
+static bool fixup_lfp_data_ptrs(const void *bdb, void *ptrs_block)
+{
+	struct bdb_lvds_lfp_data_ptrs *ptrs = ptrs_block;
+	u32 offset;
+	int i;
+
+	offset = block_offset(bdb, BDB_LVDS_LFP_DATA);
+
+	for (i = 0; i < 16; i++) {
+		if (ptrs->ptr[i].fp_timing.offset < offset ||
+		    ptrs->ptr[i].dvo_timing.offset < offset ||
+		    ptrs->ptr[i].panel_pnp_id.offset < offset)
+			return false;
+
+		ptrs->ptr[i].fp_timing.offset -= offset;
+		ptrs->ptr[i].dvo_timing.offset -= offset;
+		ptrs->ptr[i].panel_pnp_id.offset -= offset;
+	}
+
+	return true;
+}
+
 static void
 init_bdb_block(struct drm_i915_private *i915,
 	       const void *bdb, enum bdb_block_id section_id,
@@ -220,6 +243,13 @@ init_bdb_block(struct drm_i915_private *i915,
 	drm_dbg_kms(&i915->drm, "Found BDB block %d (size %zu, min size %zu)\n",
 		    section_id, block_size, min_size);
 
+	if (section_id == BDB_LVDS_LFP_DATA_PTRS &&
+	    !fixup_lfp_data_ptrs(bdb, entry->data + 3)) {
+		drm_err(&i915->drm, "VBT has malformed LFP data table pointers\n");
+		kfree(entry);
+		return;
+	}
+
 	list_add_tail(&entry->node, &i915->vbt.bdb_blocks);
 }
 
@@ -312,22 +342,19 @@ get_lvds_dvo_timing(const struct bdb_lvds_lfp_data *lvds_lfp_data,
  * this function may return NULL if the corresponding entry is invalid
  */
 static const struct lvds_fp_timing *
-get_lvds_fp_timing(const struct bdb_header *bdb,
-		   const struct bdb_lvds_lfp_data *data,
+get_lvds_fp_timing(const struct bdb_lvds_lfp_data *data,
 		   const struct bdb_lvds_lfp_data_ptrs *ptrs,
 		   int index)
 {
-	size_t data_ofs = block_offset(bdb, BDB_LVDS_LFP_DATA);
 	u16 data_size = ((const u16 *)data)[-1]; /* stored in header */
 	size_t ofs;
 
 	if (index >= ARRAY_SIZE(ptrs->ptr))
 		return NULL;
 	ofs = ptrs->ptr[index].fp_timing.offset;
-	if (ofs < data_ofs ||
-	    ofs + sizeof(struct lvds_fp_timing) > data_ofs + data_size)
+	if (ofs + sizeof(struct lvds_fp_timing) > data_size)
 		return NULL;
-	return (const struct lvds_fp_timing *)((const u8 *)bdb + ofs);
+	return (const struct lvds_fp_timing *)((const u8 *)data + ofs);
 }
 
 /* Parse general panel options */
@@ -426,7 +453,7 @@ parse_lfp_panel_dtd(struct drm_i915_private *i915,
 		    "Found panel mode in BIOS VBT legacy lfp table: " DRM_MODE_FMT "\n",
 		    DRM_MODE_ARG(panel_fixed_mode));
 
-	fp_timing = get_lvds_fp_timing(bdb, lvds_lfp_data,
+	fp_timing = get_lvds_fp_timing(lvds_lfp_data,
 				       lvds_lfp_data_ptrs,
 				       panel_type);
 	if (fp_timing) {