crypto: hisilicon/sgl - add a comment for block size initialization

mainline inclusion
from mainline-v5.13-rc1
commit 51028c6e
category: bugfix
bugzilla: 173981
CVE: NA

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=51028c6efa90ba4ab2311b0977287aac8c154f5b

----------------------------------------------------------------------

This seems "32" and "31" is obfuscating, It might be better to add a comment,
which explain it.
Signed-off-by: NKai Ye <yekai13@huawei.com>
Signed-off-by: NHerbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: NMingqiang Ling <lingmingqiang@huawei.com>
Signed-off-by: NZheng Zengkai <zhengzengkai@huawei.com>

drivers/crypto/hisilicon/sgl.c

@@ -66,6 +66,11 @@ struct hisi_acc_sgl_pool *hisi_acc_create_sgl_pool(struct device *dev,
 
 	sgl_size = sizeof(struct acc_hw_sge) * sge_nr +
 		   sizeof(struct hisi_acc_hw_sgl);
+
+	/*
+	 * the pool may allocate a block of memory of size PAGE_SIZE * 2^(MAX_ORDER - 1),
+	 * block size may exceed 2^31 on ia64, so the max of block size is 2^31
+	 */
 	block_size = 1 << (PAGE_SHIFT + MAX_ORDER <= 32 ?
 			   PAGE_SHIFT + MAX_ORDER - 1 : 31);
 	sgl_num_per_block = block_size / sgl_size;