[dpdk-dev] [PATCH 03/18] drivers: bus: dpaa: fix inconsistent struct alignment

[Andy Green <andy@warmcat.com>]

The actual descriptor for qm_mr_entry is 64-byte aligned.

But the original code plays a trick, and puts a u8 common to the
three descriptor subtypes in the union afterwards outside their
structure definitions.

Unfortunately since they compose a struct qm_fd with alignment
8, this trick destroys the ability of the compiler to understand
what has happened, resulting in this kind of problem:

/home/agreen/projects/dpdk/drivers/bus/dpaa/include/fsl_qman.h:354:3: error: alignment 1 of ‘struct <anonymous>’ is less than 8 [-Werror=packed-not-aligned]
   } __packed dcern;

on gcc 8 / Fedora 28 out of the box.

This patch moves the u8 verb into the structure definitions composed into the
union, so the alignment of the parent struct containing the alignment 8 object
can also be seen to be alignment 8 by the compiler.  Uses of .verb are fixed
up to use .ern.verb (the same offset of +0 inside all the structs in the
union).

The final struct layout should be unchanged.
---
 drivers/bus/dpaa/base/qbman/qman.c  |   14 +++++++-------
 drivers/bus/dpaa/include/fsl_qman.h |   24 +++++++++++++-----------
 2 files changed, 20 insertions(+), 18 deletions(-)

diff --git a/drivers/bus/dpaa/base/qbman/qman.c b/drivers/bus/dpaa/base/qbman/qman.c
index 2810fdd26..27d98cc10 100644
--- a/drivers/bus/dpaa/base/qbman/qman.c
+++ b/drivers/bus/dpaa/base/qbman/qman.c
@@ -314,9 +314,9 @@ static int drain_mr_fqrni(struct qm_portal *p)
 		if (!msg)
 			return 0;
 	}
-	if ((msg->verb & QM_MR_VERB_TYPE_MASK) != QM_MR_VERB_FQRNI) {
+	if ((msg->ern.verb & QM_MR_VERB_TYPE_MASK) != QM_MR_VERB_FQRNI) {
 		/* We aren't draining anything but FQRNIs */
-		pr_err("Found verb 0x%x in MR\n", msg->verb);
+		pr_err("Found verb 0x%x in MR\n", msg->ern.verb);
 		return -1;
 	}
 	qm_mr_next(p);
@@ -483,7 +483,7 @@ static inline void qm_mr_pvb_update(struct qm_portal *portal)
 	/* when accessing 'verb', use __raw_readb() to ensure that compiler
 	 * inlining doesn't try to optimise out "excess reads".
 	 */
-	if ((__raw_readb(&res->verb) & QM_MR_VERB_VBIT) == mr->vbit) {
+	if ((__raw_readb(&res->ern.verb) & QM_MR_VERB_VBIT) == mr->vbit) {
 		mr->pi = (mr->pi + 1) & (QM_MR_SIZE - 1);
 		if (!mr->pi)
 			mr->vbit ^= QM_MR_VERB_VBIT;
@@ -832,7 +832,7 @@ static u32 __poll_portal_slow(struct qman_portal *p, u32 is)
 			goto mr_done;
 		swapped_msg = *msg;
 		hw_fd_to_cpu(&swapped_msg.ern.fd);
-		verb = msg->verb & QM_MR_VERB_TYPE_MASK;
+		verb = msg->ern.verb & QM_MR_VERB_TYPE_MASK;
 		/* The message is a software ERN iff the 0x20 bit is set */
 		if (verb & 0x20) {
 			switch (verb) {
@@ -1666,7 +1666,7 @@ int qman_retire_fq(struct qman_fq *fq, u32 *flags)
 			 */
 			struct qm_mr_entry msg;
 
-			msg.verb = QM_MR_VERB_FQRNI;
+			msg.ern.verb = QM_MR_VERB_FQRNI;
 			msg.fq.fqs = mcr->alterfq.fqs;
 			msg.fq.fqid = fq->fqid;
 #ifdef CONFIG_FSL_QMAN_FQ_LOOKUP
@@ -2643,7 +2643,7 @@ int qman_shutdown_fq(u32 fqid)
 				qm_mr_pvb_update(low_p);
 				msg = qm_mr_current(low_p);
 				while (msg) {
-					if ((msg->verb &
+					if ((msg->ern.verb &
 					     QM_MR_VERB_TYPE_MASK)
 					    == QM_MR_VERB_FQRN)
 						found_fqrn = 1;
@@ -2711,7 +2711,7 @@ int qman_shutdown_fq(u32 fqid)
 			qm_mr_pvb_update(low_p);
 			msg = qm_mr_current(low_p);
 			while (msg) {
-				if ((msg->verb & QM_MR_VERB_TYPE_MASK) ==
+				if ((msg->ern.verb & QM_MR_VERB_TYPE_MASK) ==
 				    QM_MR_VERB_FQRL)
 					orl_empty = 1;
 				qm_mr_next(low_p);
diff --git a/drivers/bus/dpaa/include/fsl_qman.h b/drivers/bus/dpaa/include/fsl_qman.h
index e9793f30d..cf6dfce11 100644
--- a/drivers/bus/dpaa/include/fsl_qman.h
+++ b/drivers/bus/dpaa/include/fsl_qman.h
@@ -284,20 +284,20 @@ static inline dma_addr_t qm_sg_addr(const struct qm_sg_entry *sg)
 	} while (0)
 
 /* See 1.5.8.1: "Enqueue Command" */
-struct qm_eqcr_entry {
+struct __rte_aligned(8) qm_eqcr_entry {
 	u8 __dont_write_directly__verb;
 	u8 dca;
 	u16 seqnum;
 	u32 orp;	/* 24-bit */
 	u32 fqid;	/* 24-bit */
 	u32 tag;
-	struct qm_fd fd;
+	struct qm_fd fd; /* this has alignment 8 */
 	u8 __reserved3[32];
 } __packed;
 
 
 /* "Frame Dequeue Response" */
-struct qm_dqrr_entry {
+struct __rte_aligned(8) qm_dqrr_entry {
 	u8 verb;
 	u8 stat;
 	u16 seqnum;	/* 15-bit */
@@ -305,7 +305,7 @@ struct qm_dqrr_entry {
 	u8 __reserved2[3];
 	u32 fqid;	/* 24-bit */
 	u32 contextB;
-	struct qm_fd fd;
+	struct qm_fd fd; /* this has alignment 8 */
 	u8 __reserved4[32];
 };
 
@@ -323,18 +323,19 @@ struct qm_dqrr_entry {
 /* "ERN Message Response" */
 /* "FQ State Change Notification" */
 struct qm_mr_entry {
-	u8 verb;
 	union {
 		struct {
+			u8 verb;
 			u8 dca;
 			u16 seqnum;
 			u8 rc;		/* Rejection Code */
 			u32 orp:24;
 			u32 fqid;	/* 24-bit */
 			u32 tag;
-			struct qm_fd fd;
-		} __packed ern;
+			struct qm_fd fd; /* this has alignment 8 */
+		} __packed __rte_aligned(8) ern;
 		struct {
+			u8 verb;
 #if __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__
 			u8 colour:2;	/* See QM_MR_DCERN_COLOUR_* */
 			u8 __reserved1:4;
@@ -349,18 +350,19 @@ struct qm_mr_entry {
 			u32 __reserved3:24;
 			u32 fqid;	/* 24-bit */
 			u32 tag;
-			struct qm_fd fd;
-		} __packed dcern;
+			struct qm_fd fd; /* this has alignment 8 */
+		} __packed __rte_aligned(8) dcern;
 		struct {
+			u8 verb;
 			u8 fqs;		/* Frame Queue Status */
 			u8 __reserved1[6];
 			u32 fqid;	/* 24-bit */
 			u32 contextB;
 			u8 __reserved2[16];
-		} __packed fq;		/* FQRN/FQRNI/FQRL/FQPN */
+		} __packed __rte_aligned(8) fq;		/* FQRN/FQRNI/FQRL/FQPN */
 	};
 	u8 __reserved2[32];
-} __packed;
+} __packed __rte_aligned(8);
 #define QM_MR_VERB_VBIT			0x80
 /*
  * ERNs originating from direct-connect portals ("dcern") use 0x20 as a verb