I think it looks something like this ...

@@ -211,23 +211,18 @@ struct iomap_readpage_ctx {
 };

 static void iomap_read_inline_data(struct inode *inode, struct folio *folio,
-               struct iomap *iomap)
+               struct iomap *iomap, loff_t pos, size_t size)
 {
-       size_t size = i_size_read(inode);
        void *addr;
+       size_t offset = offset_in_folio(folio, pos);

-       if (folio_test_uptodate(folio))
-               return;
+       BUG_ON(size != i_size_read(inode) - pos);

-       BUG_ON(folio->index);
-       BUG_ON(folio_multi(folio));
-       BUG_ON(size > PAGE_SIZE - offset_in_page(iomap->inline_data));
-
-       addr = kmap_local_folio(folio, 0);
+       addr = kmap_local_folio(folio, offset);
        memcpy(addr, iomap->inline_data, size);
        memset(addr + size, 0, PAGE_SIZE - size);
        kunmap_local(addr);
-       folio_mark_uptodate(folio);
+       iomap_set_range_uptodate(folio, to_iomap_page(folio), pos, size);