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From: Rosen Penev <rosenp@gmail.com>
To: linux-wireless@vger.kernel.org
Cc: "John W. Linville" <linville@tuxdriver.com>,
	Michael Buesch <mb@bu3sch.de>,
	b43-dev@lists.infradead.org (open list:B43 WIRELESS DRIVER),
	linux-kernel@vger.kernel.org (open list)
Subject: [PATCH wireless] wifi: b43: map the RX buffers DMA_BIDIRECTIONAL
Date: Fri, 23 Oct 2026 12:06:53 -0700	[thread overview]
Message-ID: <20261023190653.70741-1-rosenp@gmail.com> (raw)

b43 poisons each RX buffer before it hands it to the device, and drops
a buffer that still carries the poison, as the device sometimes skips
one. The RX buffers are mapped and synced DMA_FROM_DEVICE. On a
non-coherent CPU like the BCM4716 or the BCM4708, the map and the sync
for the device then only invalidate the cache, so the poison written
just before never reaches memory. A skipped buffer is read as whatever
the memory held before, for a recycled buffer the data of its previous
use: garbage frames, or a length that sends dma_rx() into its path for
frames spanning several buffers.

Map, sync and unmap the RX buffers DMA_BIDIRECTIONAL, so that the
poison is written back before the device gets the buffer.

Reported on a Netgear R6400 (BCM4708, BCM4331).

Fixes: cf68636a9773 ("b43: Refresh RX poison on buffer recycling")
Signed-off-by: Rosen Penev <rosenp@gmail.com>
---
 drivers/net/wireless/broadcom/b43/dma.c | 14 ++++++++++----
 1 file changed, 10 insertions(+), 4 deletions(-)

diff --git a/drivers/net/wireless/broadcom/b43/dma.c b/drivers/net/wireless/broadcom/b43/dma.c
index 05da6987a845..c8585c6dff37 100644
--- a/drivers/net/wireless/broadcom/b43/dma.c
+++ b/drivers/net/wireless/broadcom/b43/dma.c
@@ -353,8 +353,14 @@ static inline
 		dmaaddr = dma_map_single(ring->dev->dev->dma_dev,
 					 buf, len, DMA_TO_DEVICE);
 	} else {
+		/*
+		 * Not DMA_FROM_DEVICE: on a non-coherent CPU, the map and
+		 * the sync for the device would then only invalidate the
+		 * cache, and the poison of b43_poison_rx_buffer() would
+		 * never reach memory.
+		 */
 		dmaaddr = dma_map_single(ring->dev->dev->dma_dev,
-					 buf, len, DMA_FROM_DEVICE);
+					 buf, len, DMA_BIDIRECTIONAL);
 	}
 
 	return dmaaddr;
@@ -369,7 +375,7 @@ static inline
 				 addr, len, DMA_TO_DEVICE);
 	} else {
 		dma_unmap_single(ring->dev->dev->dma_dev,
-				 addr, len, DMA_FROM_DEVICE);
+				 addr, len, DMA_BIDIRECTIONAL);
 	}
 }
 
@@ -379,7 +385,7 @@ static inline
 {
 	B43_WARN_ON(ring->tx);
 	dma_sync_single_for_cpu(ring->dev->dev->dma_dev,
-				    addr, len, DMA_FROM_DEVICE);
+				    addr, len, DMA_BIDIRECTIONAL);
 }
 
 static inline
@@ -388,7 +394,7 @@ static inline
 {
 	B43_WARN_ON(ring->tx);
 	dma_sync_single_for_device(ring->dev->dev->dma_dev,
-				   addr, len, DMA_FROM_DEVICE);
+				   addr, len, DMA_BIDIRECTIONAL);
 }
 
 static inline
-- 
2.56.0


_______________________________________________
b43-dev mailing list
b43-dev@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/b43-dev

WARNING: multiple messages have this Message-ID (diff)
From: Rosen Penev <rosenp@gmail.com>
To: linux-wireless@vger.kernel.org
Cc: "John W. Linville" <linville@tuxdriver.com>,
	Michael Buesch <mb@bu3sch.de>,
	b43-dev@lists.infradead.org (open list:B43 WIRELESS DRIVER),
	linux-kernel@vger.kernel.org (open list)
Subject: [PATCH wireless] wifi: b43: map the RX buffers DMA_BIDIRECTIONAL
Date: Fri, 23 Oct 2026 12:06:53 -0700	[thread overview]
Message-ID: <20261023190653.70741-1-rosenp@gmail.com> (raw)

b43 poisons each RX buffer before it hands it to the device, and drops
a buffer that still carries the poison, as the device sometimes skips
one. The RX buffers are mapped and synced DMA_FROM_DEVICE. On a
non-coherent CPU like the BCM4716 or the BCM4708, the map and the sync
for the device then only invalidate the cache, so the poison written
just before never reaches memory. A skipped buffer is read as whatever
the memory held before, for a recycled buffer the data of its previous
use: garbage frames, or a length that sends dma_rx() into its path for
frames spanning several buffers.

Map, sync and unmap the RX buffers DMA_BIDIRECTIONAL, so that the
poison is written back before the device gets the buffer.

Reported on a Netgear R6400 (BCM4708, BCM4331).

Fixes: cf68636a9773 ("b43: Refresh RX poison on buffer recycling")
Signed-off-by: Rosen Penev <rosenp@gmail.com>
---
 drivers/net/wireless/broadcom/b43/dma.c | 14 ++++++++++----
 1 file changed, 10 insertions(+), 4 deletions(-)

diff --git a/drivers/net/wireless/broadcom/b43/dma.c b/drivers/net/wireless/broadcom/b43/dma.c
index 05da6987a845..c8585c6dff37 100644
--- a/drivers/net/wireless/broadcom/b43/dma.c
+++ b/drivers/net/wireless/broadcom/b43/dma.c
@@ -353,8 +353,14 @@ static inline
 		dmaaddr = dma_map_single(ring->dev->dev->dma_dev,
 					 buf, len, DMA_TO_DEVICE);
 	} else {
+		/*
+		 * Not DMA_FROM_DEVICE: on a non-coherent CPU, the map and
+		 * the sync for the device would then only invalidate the
+		 * cache, and the poison of b43_poison_rx_buffer() would
+		 * never reach memory.
+		 */
 		dmaaddr = dma_map_single(ring->dev->dev->dma_dev,
-					 buf, len, DMA_FROM_DEVICE);
+					 buf, len, DMA_BIDIRECTIONAL);
 	}
 
 	return dmaaddr;
@@ -369,7 +375,7 @@ static inline
 				 addr, len, DMA_TO_DEVICE);
 	} else {
 		dma_unmap_single(ring->dev->dev->dma_dev,
-				 addr, len, DMA_FROM_DEVICE);
+				 addr, len, DMA_BIDIRECTIONAL);
 	}
 }
 
@@ -379,7 +385,7 @@ static inline
 {
 	B43_WARN_ON(ring->tx);
 	dma_sync_single_for_cpu(ring->dev->dev->dma_dev,
-				    addr, len, DMA_FROM_DEVICE);
+				    addr, len, DMA_BIDIRECTIONAL);
 }
 
 static inline
@@ -388,7 +394,7 @@ static inline
 {
 	B43_WARN_ON(ring->tx);
 	dma_sync_single_for_device(ring->dev->dev->dma_dev,
-				   addr, len, DMA_FROM_DEVICE);
+				   addr, len, DMA_BIDIRECTIONAL);
 }
 
 static inline
-- 
2.56.0


             reply	other threads:[~2026-10-23 19:07 UTC|newest]

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2026-10-23 19:06 Rosen Penev [this message]
2026-10-23 19:06 ` [PATCH wireless] wifi: b43: map the RX buffers DMA_BIDIRECTIONAL Rosen Penev
2026-10-23 20:14 ` Michael Büsch
2026-10-23 20:14   ` Michael Büsch
2026-10-23 20:41   ` Michael Büsch
2026-10-23 20:41     ` Michael Büsch
2026-10-23 20:44     ` Rosen Penev
2026-10-23 20:44       ` Rosen Penev
2026-10-23 20:57       ` Michael Büsch
2026-10-23 20:57         ` Michael Büsch
2026-10-23 21:21         ` Rosen Penev
2026-10-23 21:21           ` Rosen Penev
2026-10-23 21:39           ` Michael Büsch
2026-10-23 21:39             ` Michael Büsch

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