[Cbe-oss-dev] [PATCH 1/3] spufs context switch - spu mfc save

[Luke Browning]

Fix mfc control register save.

Need to preserve the current contents of the register since there
are status bits that are used to drive restore.

Based on comments and patches from Gerhard Stenzel and Jeremy Kerr.

Signed-off-by: Luke Browning <lukebrowning at us.ibm.com>
---
 arch/powerpc/platforms/cell/spufs/switch.c |   22 ++++++++++++++--------
 1 files changed, 14 insertions(+), 8 deletions(-)

Index: public_git/arch/powerpc/platforms/cell/spufs/switch.c
===================================================================
--- public_git.orig/arch/powerpc/platforms/cell/spufs/switch.c
+++ public_git/arch/powerpc/platforms/cell/spufs/switch.c
@@ -186,20 +186,25 @@ static inline void save_mfc_cntl(struct 
 				 MFC_CNTL_SUSPEND_COMPLETE);
 		/* fall through */
 	case MFC_CNTL_SUSPEND_COMPLETE:
-		if (csa) {
-			csa->priv2.mfc_control_RW =
-				MFC_CNTL_SUSPEND_MASK |
-				MFC_CNTL_SUSPEND_DMA_QUEUE;
-		}
+		/*
+		 * This state is seen during a page fault.  The hardware
+		 * automatically stops the mfc which is reflected in the
+		 * control register.  If a fault occurs, the spu needs
+		 * to be retarted with the mfc restart bit, which occurs
+		 * in restore_mfc_cntl.  The flag MFC_CNTL_SUSPEND_DMA_QUEUE
+		 * is used as a flag between these two pieces of code.
+		 */
+		csa->priv2.mfc_control_RW = in_be64(&priv2->mfc_control_RW) |
+					MFC_CNTL_SUSPEND_DMA_QUEUE;
 		break;
 	case MFC_CNTL_NORMAL_DMA_QUEUE_OPERATION:
 		out_be64(&priv2->mfc_control_RW, MFC_CNTL_SUSPEND_DMA_QUEUE);
 		POLL_WHILE_FALSE((in_be64(&priv2->mfc_control_RW) &
 				  MFC_CNTL_SUSPEND_DMA_STATUS_MASK) ==
 				 MFC_CNTL_SUSPEND_COMPLETE);
-		if (csa) {
-			csa->priv2.mfc_control_RW = 0;
-		}
+
+		csa->priv2.mfc_control_RW = in_be64(&priv2->mfc_control_RW) &
+					~MFC_CNTL_SUSPEND_DMA_QUEUE;
 		break;
 	}
 }
@@ -1721,12 +1726,8 @@ static inline void restore_mfc_cntl(stru
 	 */
 	out_be64(&priv2->mfc_control_RW, csa->priv2.mfc_control_RW);
 	eieio();
-	/*
-	 * FIXME: this is to restart a DMA that we were processing
-	 *        before the save. better remember the fault information
-	 *        in the csa instead.
-	 */
-	if ((csa->priv2.mfc_control_RW & MFC_CNTL_SUSPEND_DMA_QUEUE_MASK)) {
+
+	if (csa->priv2.mfc_control_RW & MFC_CNTL_SUSPEND_DMA_QUEUE) {
 		out_be64(&priv2->mfc_control_RW, MFC_CNTL_RESTART_DMA_COMMAND);
 		eieio();
 	}