MFC r310754

sfxge(4): don't use Tx descriptor push with TSO option descriptors

It is not safe to push TSO option descriptors if pacer bypass is
enabled, so to make sure that doesn't happen never push TSO option
descriptors.

Submitted by:   Mark Spender <mspender at solarflare.com>
Sponsored by:   Solarflare Communications, Inc.

1 files changed, 43 insertions, 13 deletions

diff --git a/sys/dev/sfxge/common/ef10_tx.c b/sys/dev/sfxge/common/ef10_tx.c
index a4729a1..2b0ec5e 100755
--- a/sys/dev/sfxge/common/ef10_tx.c
+++ b/sys/dev/sfxge/common/ef10_tx.c
@@ -470,9 +470,9 @@ fail1:
 }
 
 /*
- * This improves performance by pushing a TX descriptor at the same time as the
- * doorbell. The descriptor must be added to the TXQ, so that can be used if the
- * hardware decides not to use the pushed descriptor.
+ * This improves performance by, when possible, pushing a TX descriptor at the
+ * same time as the doorbell. The descriptor must be added to the TXQ, so that
+ * can be used if the hardware decides not to use the pushed descriptor.
  */
 			void
 ef10_tx_qpush(
@@ -492,16 +492,46 @@ ef10_tx_qpush(
 	offset = id * sizeof (efx_qword_t);
 
 	EFSYS_MEM_READQ(etp->et_esmp, offset, &desc);
-	EFX_POPULATE_OWORD_3(oword,
-	    ERF_DZ_TX_DESC_WPTR, wptr,
-	    ERF_DZ_TX_DESC_HWORD, EFX_QWORD_FIELD(desc, EFX_DWORD_1),
-	    ERF_DZ_TX_DESC_LWORD, EFX_QWORD_FIELD(desc, EFX_DWORD_0));
-
-	/* Guarantee ordering of memory (descriptors) and PIO (doorbell) */
-	EFX_DMA_SYNC_QUEUE_FOR_DEVICE(etp->et_esmp, etp->et_mask + 1, wptr, id);
-	EFSYS_PIO_WRITE_BARRIER();
-	EFX_BAR_TBL_DOORBELL_WRITEO(enp, ER_DZ_TX_DESC_UPD_REG, etp->et_index,
-				    &oword);
+
+	/*
+	 * SF Bug 65776: TSO option descriptors cannot be pushed if pacer bypass
+	 * is enabled on the event queue this transmit queue is attached to.
+	 *
+	 * To ensure the code is safe, it is easiest to simply test the type of
+	 * the descriptor to push, and only push it is if it not a TSO option
+	 * descriptor.
+	 */
+	if ((EFX_QWORD_FIELD(desc, ESF_DZ_TX_DESC_IS_OPT) != 1) ||
+	    (EFX_QWORD_FIELD(desc, ESF_DZ_TX_OPTION_TYPE) !=
+	    ESE_DZ_TX_OPTION_DESC_TSO)) {
+		/* Push the descriptor and update the wptr. */
+		EFX_POPULATE_OWORD_3(oword, ERF_DZ_TX_DESC_WPTR, wptr,
+		    ERF_DZ_TX_DESC_HWORD, EFX_QWORD_FIELD(desc, EFX_DWORD_1),
+		    ERF_DZ_TX_DESC_LWORD, EFX_QWORD_FIELD(desc, EFX_DWORD_0));
+
+		/* Ensure ordering of memory (descriptors) and PIO (doorbell) */
+		EFX_DMA_SYNC_QUEUE_FOR_DEVICE(etp->et_esmp, etp->et_mask + 1,
+					    wptr, id);
+		EFSYS_PIO_WRITE_BARRIER();
+		EFX_BAR_TBL_DOORBELL_WRITEO(enp, ER_DZ_TX_DESC_UPD_REG,
+					    etp->et_index, &oword);
+	} else {
+		efx_dword_t dword;
+
+		/*
+		 * Only update the wptr. This is signalled to the hardware by
+		 * only writing one DWORD of the doorbell register.
+		 */
+		EFX_POPULATE_OWORD_1(oword, ERF_DZ_TX_DESC_WPTR, wptr);
+		dword = oword.eo_dword[2];
+
+		/* Ensure ordering of memory (descriptors) and PIO (doorbell) */
+		EFX_DMA_SYNC_QUEUE_FOR_DEVICE(etp->et_esmp, etp->et_mask + 1,
+					    wptr, id);
+		EFSYS_PIO_WRITE_BARRIER();
+		EFX_BAR_TBL_WRITED2(enp, ER_DZ_TX_DESC_UPD_REG,
+				    etp->et_index, &dword, B_FALSE);
+	}
 }
 
 	__checkReturn	efx_rc_t