netdev - [PATCH] net: atlantic: fix ring buffer alignment

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Date: Fri, 16 Jun 2023 11:26:32 +0200
From: Arnd Bergmann <arnd@...nel.org>
To: Igor Russkikh <irusskikh@...vell.com>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>,
	Paolo Abeni <pabeni@...hat.com>
Cc: Arnd Bergmann <arnd@...db.de>,
	Nathan Chancellor <nathan@...nel.org>,
	Nick Desaulniers <ndesaulniers@...gle.com>,
	Tom Rix <trix@...hat.com>,
	netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	llvm@...ts.linux.dev
Subject: [PATCH] net: atlantic: fix ring buffer alignment

From: Arnd Bergmann <arnd@...db.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@...db.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