linux-kernel - [PATCH 1/2] et131x: Correct WRAP bit handling

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Message-ID: <20091012143813.20944.66683.stgit@localhost.localdomain>
Date:	Mon, 12 Oct 2009 15:38:17 +0100
From:	Alan Cox <alan@...ux.intel.com>
To:	greg@...ah.com, linux-kernel@...r.kernel.org
Subject: [PATCH 1/2] et131x: Correct WRAP bit handling

add_10bit loses the existing wrap value

Signed-off-by: Alan Cox <alan@...ux.intel.com>
---

 drivers/staging/et131x/et1310_rx.c |   20 ++++++++++++++------
 1 files changed, 14 insertions(+), 6 deletions(-)


diff --git a/drivers/staging/et131x/et1310_rx.c b/drivers/staging/et131x/et1310_rx.c
index 8f2e91f..10e21db 100644
--- a/drivers/staging/et131x/et1310_rx.c
+++ b/drivers/staging/et131x/et1310_rx.c
@@ -1177,12 +1177,20 @@ void et131x_handle_recv_interrupt(struct et131x_adapter *etdev)
 
 static inline u32 bump_fbr(u32 *fbr, u32 limit)
 {
-	u32 v = *fbr;
-	add_10bit(&v, 1);
-	if (v > limit)
-		v = (*fbr & ~ET_DMA10_MASK) ^ ET_DMA10_WRAP;
-	*fbr = v;
-	return v;
+        u32 v = *fbr;
+        v++;
+        /* This works for all cases where limit < 1024. The 1023 case
+           works because 1023++ is 1024 which means the if condition is not
+           taken but the carry of the bit into the wrap bit toggles the wrap
+           value correctly */
+        if ((v & ET_DMA10_MASK) > limit) {
+                v &= ~ET_DMA10_MASK;
+                v ^= ET_DMA10_WRAP;
+        }
+        /* For the 1023 case */
+        v &= (ET_DMA10_MASK|ET_DMA10_WRAP);
+        *fbr = v;
+        return v;
 }
 
 /**

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