drm/i915/bios: Generate LFP data table pointers if the VBT lacks them

Modern VBTs no longer contain the LFP data table pointers
block (41). We are expecting to have one in order to be able
to parse the LFP data block (42), so let's make one up.

Since the fp_timing table has variable size we must somehow
determine its size. Rather than just hardcode it we look for
the terminator bytes (0xffff) to figure out where each table
entry starts. dvo_timing, panel_pnp_id, and panel_name are
expected to have fixed size.

This has been observed on various machines, eg. TGL with BDB
version 240, CML with BDB version 231, etc. The most recent
VBT I've observed that still had block 41 had BDB version
228. So presumably the cutoff (if an exact cutoff even exists)
is somewhere around BDB version 229-231.

v2: kfree the thing we allocated, not the thing+3 bytes
v3: Do the debugprint only if we found the LFP data block
v4: Fix t0 null check (Jani)
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220504150440.13748-3-ville.syrjala@linux.intel.com

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

@@ -310,16 +310,144 @@ static bool fixup_lfp_data_ptrs(const void *bdb, void *ptrs_block)
 	return validate_lfp_data_ptrs(bdb, ptrs);
 }
 
+static const void *find_fp_timing_terminator(const u8 *data, int size)
+{
+	int i;
+
+	for (i = 0; i < size - 1; i++) {
+		if (data[i] == 0xff && data[i+1] == 0xff)
+			return &data[i];
+	}
+
+	return NULL;
+}
+
+static int make_lfp_data_ptr(struct lvds_lfp_data_ptr_table *table,
+			     int table_size, int total_size)
+{
+	if (total_size < table_size)
+		return total_size;
+
+	table->table_size = table_size;
+	table->offset = total_size - table_size;
+
+	return total_size - table_size;
+}
+
+static void next_lfp_data_ptr(struct lvds_lfp_data_ptr_table *next,
+			      const struct lvds_lfp_data_ptr_table *prev,
+			      int size)
+{
+	next->table_size = prev->table_size;
+	next->offset = prev->offset + size;
+}
+
+static void *generate_lfp_data_ptrs(struct drm_i915_private *i915,
+				    const void *bdb)
+{
+	int i, size, table_size, block_size, offset;
+	const void *t0, *t1, *block;
+	struct bdb_lvds_lfp_data_ptrs *ptrs;
+	void *ptrs_block;
+
+	block = find_raw_section(bdb, BDB_LVDS_LFP_DATA);
+	if (!block)
+		return NULL;
+
+	drm_dbg_kms(&i915->drm, "Generating LFP data table pointers\n");
+
+	block_size = get_blocksize(block);
+
+	size = block_size;
+	t0 = find_fp_timing_terminator(block, size);
+	if (!t0)
+		return NULL;
+
+	size -= t0 - block - 2;
+	t1 = find_fp_timing_terminator(t0 + 2, size);
+	if (!t1)
+		return NULL;
+
+	size = t1 - t0;
+	if (size * 16 > block_size)
+		return NULL;
+
+	ptrs_block = kzalloc(sizeof(*ptrs) + 3, GFP_KERNEL);
+	if (!ptrs_block)
+		return NULL;
+
+	*(u8 *)(ptrs_block + 0) = BDB_LVDS_LFP_DATA_PTRS;
+	*(u16 *)(ptrs_block + 1) = sizeof(*ptrs);
+	ptrs = ptrs_block + 3;
+
+	table_size = sizeof(struct lvds_pnp_id);
+	size = make_lfp_data_ptr(&ptrs->ptr[0].panel_pnp_id, table_size, size);
+
+	table_size = sizeof(struct lvds_dvo_timing);
+	size = make_lfp_data_ptr(&ptrs->ptr[0].dvo_timing, table_size, size);
+
+	table_size = t0 - block + 2;
+	size = make_lfp_data_ptr(&ptrs->ptr[0].fp_timing, table_size, size);
+
+	if (ptrs->ptr[0].fp_timing.table_size)
+		ptrs->lvds_entries++;
+	if (ptrs->ptr[0].dvo_timing.table_size)
+		ptrs->lvds_entries++;
+	if (ptrs->ptr[0].panel_pnp_id.table_size)
+		ptrs->lvds_entries++;
+
+	if (size != 0 || ptrs->lvds_entries != 3) {
+		kfree(ptrs);
+		return NULL;
+	}
+
+	size = t1 - t0;
+	for (i = 1; i < 16; i++) {
+		next_lfp_data_ptr(&ptrs->ptr[i].fp_timing, &ptrs->ptr[i-1].fp_timing, size);
+		next_lfp_data_ptr(&ptrs->ptr[i].dvo_timing, &ptrs->ptr[i-1].dvo_timing, size);
+		next_lfp_data_ptr(&ptrs->ptr[i].panel_pnp_id, &ptrs->ptr[i-1].panel_pnp_id, size);
+	}
+
+	size = t1 - t0;
+	table_size = sizeof(struct lvds_lfp_panel_name);
+
+	if (16 * (size + table_size) <= block_size) {
+		ptrs->panel_name.table_size = table_size;
+		ptrs->panel_name.offset = size * 16;
+	}
+
+	offset = block - bdb;
+
+	for (i = 0; i < 16; i++) {
+		ptrs->ptr[i].fp_timing.offset += offset;
+		ptrs->ptr[i].dvo_timing.offset += offset;
+		ptrs->ptr[i].panel_pnp_id.offset += offset;
+	}
+
+	if (ptrs->panel_name.table_size)
+		ptrs->panel_name.offset += offset;
+
+	return ptrs_block;
+}
+
 static void
 init_bdb_block(struct drm_i915_private *i915,
 	       const void *bdb, enum bdb_block_id section_id,
 	       size_t min_size)
 {
 	struct bdb_block_entry *entry;
+	void *temp_block = NULL;
 	const void *block;
 	size_t block_size;
 
 	block = find_raw_section(bdb, section_id);
+
+	/* Modern VBTs lack the LFP data table pointers block, make one up */
+	if (!block && section_id == BDB_LVDS_LFP_DATA_PTRS) {
+		temp_block = generate_lfp_data_ptrs(i915, bdb);
+		if (temp_block)
+			block = temp_block + 3;
+	}
 	if (!block)
 		return;
 
@@ -330,12 +458,16 @@ init_bdb_block(struct drm_i915_private *i915,
 
 	entry = kzalloc(struct_size(entry, data, max(min_size, block_size) + 3),
 			GFP_KERNEL);
-	if (!entry)
+	if (!entry) {
+		kfree(temp_block);
 		return;
+	}
 
 	entry->section_id = section_id;
 	memcpy(entry->data, block - 3, block_size + 3);
 
+	kfree(temp_block);
+
 	drm_dbg_kms(&i915->drm, "Found BDB block %d (size %zu, min size %zu)\n",
 		    section_id, block_size, min_size);