wifi: mt76: mt7915: honour the valid flag in efuse block reads

The EFUSE_ACCESS response carries a valid flag that was ignored, so
reading an unwritten efuse block copied garbage into the eeprom data.
Return -ENODATA for invalid blocks and leave the corresponding eeprom
range untouched (zero-initialised) when loading the full eeprom from
efuse.

Fixes: e57b7901469f ("mt76: add mac80211 driver for MT7915 PCIe-based chipsets")
Signed-off-by: Felix Fietkau <[email protected]>

mt7915/eeprom.c

@@ -150,11 +150,11 @@ static int mt7915_eeprom_load(struct mt7915_dev *dev)
 		if (free_block_num >= 29)
 			return -EINVAL;
 
-		/* read eeprom data from efuse */
+		/* read eeprom data from efuse, skipping unwritten blocks */
 		block_num = DIV_ROUND_UP(eeprom_size, eeprom_blk_size);
 		for (i = 0; i < block_num; i++) {
 			ret = mt7915_mcu_get_eeprom(dev, i * eeprom_blk_size, NULL);
-			if (ret < 0)
+			if (ret < 0 && ret != -ENODATA)
 				return ret;
 		}
 	}

mt7915/mcu.c

@@ -2957,6 +2957,11 @@ int mt7915_mcu_get_eeprom(struct mt7915_dev *dev, u32 offset, u8 *read_buf)
 		return -EINVAL;
 	}
 
+	if (!le32_to_cpu(res->valid)) {
+		dev_kfree_skb(skb);
+		return -ENODATA;
+	}
+
 	if (!buf) {
 		u32 addr = le32_to_cpu(res->addr);