[PATCH] net: atlantic: fix ring buffer alignment

Arnd Bergmann
2023-06-16T09:26:51Z

From: Arnd Bergmann <arnd@arndb.de>

clang warns about conflicting packing annotations:

drivers/net/ethernet/aquantia/atlantic/aq_ring.h:72:2: error: field within 'struct aq_ring_buff_s' is less aligned than 'union aq_ring_buff_s::(anonymous at drivers/net/ethernet/aquantia/atlantic/aq_ring.h:72:2)' and is usually due to 'struct aq_ring_buff_s' being packed, which can lead to unaligned accesses [-Werror,-Wunaligned-access]

This was originally intended to ensure the structure fits exactly into
32 bytes on 64-bit architectures, but apparently never did, and instead
just produced misaligned pointers as well as forcing byte-wise access
on hardware without unaligned load/store instructions.

Update the comment to more closely reflect the layout and remove the
broken __packed annotation.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
---
.../net/ethernet/aquantia/atlantic/aq_ring.h | 26 +++++++++++--------
1 file changed, 15 insertions(+), 11 deletions(-)

diff --git a/drivers/net/ethernet/aquantia/atlantic/aq_ring.h b/drivers/net/ethernet/aquantia/atlantic/aq_ring.h
index 0a6c34438c1d0..a9cc5a1c4c479 100644
--- a/drivers/net/ethernet/aquantia/atlantic/aq_ring.h
+++ b/drivers/net/ethernet/aquantia/atlantic/aq_ring.h
@@ -26,19 +26,23 @@ struct aq_rxpage {
unsigned int pg_off;
};

-/* TxC SOP DX EOP
- * +----------+----------+----------+-----------
- * 8bytes|len l3,l4 | pa | pa | pa
- * +----------+----------+----------+-----------
- * 4/8bytes|len pkt |len pkt | | skb
- * +----------+----------+----------+-----------
- * 4/8bytes|is_gso |len,flags |len |len,is_eop
- * +----------+----------+----------+-----------
+/* TxC SOP DX EOP RX
+ * +----------+----------+----------+----------+-------
+ * 8bytes|len l3,l4 | pa | pa | pa | hash
+ * +----------+----------+----------+----------+-------
+ * 4/8bytes|len pkt |len pkt | | skb | page
+ * +----------+----------+----------+----------+-------
+ * 4/8bytes|is_gso |len,flags |len |len,is_eop| daddr
+ * +----------+----------+----------+----------+-------
+ * 4/8bytes| | | | | order,pgoff
+ * +----------+----------+----------+----------+-------
+ * 2bytes | | | | | vlan_rx_tag
+ * +----------+----------+----------+----------+-------
+ * 8bytes + flags
+ * +----------+----------+----------+----------+-------
*
- * This aq_ring_buff_s doesn't have endianness dependency.
- * It is __packed for cache line optimizations.
*/
-struct __packed aq_ring_buff_s {
+struct aq_ring_buff_s {
union {
/* RX/TX */
dma_addr_t pa;
--
2.39.2