[RFC PATCH v2 0/4] staging: vt6655: Implement allocation failure handling

[RFC PATCH v2 0/4] staging: vt6655: Implement allocation failure handling

[Nam Cao]

This driver does not handle allocation failure when receiving data very
well. This patchset implements better handling in the case of allocation
failure.

Also do some necessary clean-up to implement this.

v2:
  - squash 3 commits that were doing a single thing
  - add new commit which removes a redundant assignment
  - take device_init_rx_desc() out of unnecessary else condition.
  - remove return statement at the end of void function
  - add a missing rd = rd->next statement in device_rx_srv(): because
    we already drop the current buffer, we should move on to the next
    buffer in the ring where new data will be written to.

Nam Cao (4):
  staging: vt6655: remove redundant if condition
  staging: vt6655: change vnt_receive_frame return type to void
  staging: vt6655: remove redundant assignment
  staging: vt6655: implement allocation failure handling

 drivers/staging/vt6655/device_main.c | 40 +++++++++++++++++-----------
 drivers/staging/vt6655/dpc.c         |  8 +++---
 drivers/staging/vt6655/dpc.h         |  2 +-
 3 files changed, 28 insertions(+), 22 deletions(-)

-- 
2.25.1

[RFC PATCH v2 1/4] staging: vt6655: remove redundant if condition

[Nam Cao]

The function vnt_receive_frame always returns true, so checking its
return value is redundant. Remove it.

Signed-off-by: Nam Cao <namcaov@gmail.com>
---
 drivers/staging/vt6655/device_main.c | 12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/drivers/staging/vt6655/device_main.c b/drivers/staging/vt6655/device_main.c
index 56c3cf3ba53d..21d10d9fde47 100644
--- a/drivers/staging/vt6655/device_main.c
+++ b/drivers/staging/vt6655/device_main.c
@@ -832,12 +832,12 @@ static int device_rx_srv(struct vnt_private *priv, unsigned int idx)
 		if (!rd->rd_info->skb)
 			break;
 
-		if (vnt_receive_frame(priv, rd)) {
-			if (!device_alloc_rx_buf(priv, rd)) {
-				dev_err(&priv->pcid->dev,
-					"can not allocate rx buf\n");
-				break;
-			}
+		vnt_receive_frame(priv, rd);
+
+		if (!device_alloc_rx_buf(priv, rd)) {
+			dev_err(&priv->pcid->dev,
+				"can not allocate rx buf\n");
+			break;
 		}
 		rd->rd0.owner = OWNED_BY_NIC;
 	}
-- 
2.25.1

[RFC PATCH v2 2/4] staging: vt6655: change vnt_receive_frame return type to void

[Nam Cao]

The function vnt_receive_frame's returned value is not used anywhere.
Furthermore, it always return true. Change its return type to void.

Signed-off-by: Nam Cao <namcaov@gmail.com>
---
 drivers/staging/vt6655/dpc.c | 8 +++-----
 drivers/staging/vt6655/dpc.h | 2 +-
 2 files changed, 4 insertions(+), 6 deletions(-)

diff --git a/drivers/staging/vt6655/dpc.c b/drivers/staging/vt6655/dpc.c
index c6ed3537f439..3bf60039fa9a 100644
--- a/drivers/staging/vt6655/dpc.c
+++ b/drivers/staging/vt6655/dpc.c
@@ -115,7 +115,7 @@ static bool vnt_rx_data(struct vnt_private *priv, struct sk_buff *skb,
 	return true;
 }
 
-bool vnt_receive_frame(struct vnt_private *priv, struct vnt_rx_desc *curr_rd)
+void vnt_receive_frame(struct vnt_private *priv, struct vnt_rx_desc *curr_rd)
 {
 	struct vnt_rd_info *rd_info = curr_rd->rd_info;
 	struct sk_buff *skb;
@@ -133,13 +133,11 @@ bool vnt_receive_frame(struct vnt_private *priv, struct vnt_rx_desc *curr_rd)
 		/* Frame Size error drop this packet.*/
 		dev_dbg(&priv->pcid->dev, "Wrong frame size %d\n", frame_size);
 		dev_kfree_skb_irq(skb);
-		return true;
+		return;
 	}
 
 	if (vnt_rx_data(priv, skb, frame_size))
-		return true;
+		return;
 
 	dev_kfree_skb_irq(skb);
-
-	return true;
 }
diff --git a/drivers/staging/vt6655/dpc.h b/drivers/staging/vt6655/dpc.h
index 40364c0ab7f6..f67c1ef23171 100644
--- a/drivers/staging/vt6655/dpc.h
+++ b/drivers/staging/vt6655/dpc.h
@@ -16,6 +16,6 @@
 
 #include "device.h"
 
-bool vnt_receive_frame(struct vnt_private *priv, struct vnt_rx_desc *curr_rd);
+void vnt_receive_frame(struct vnt_private *priv, struct vnt_rx_desc *curr_rd);
 
 #endif /* __RXTX_H__ */
-- 
2.25.1

[RFC PATCH v2 3/4] staging: vt6655: remove redundant assignment

[Nam Cao]

In function device_rx_srv, the assignment rd->rd0.owner = OWNED_BY_NIC
is redundant because this is already done in device_alloc_rx_buf() which
is called right above. Remove it.

Signed-off-by: Nam Cao <namcaov@gmail.com>
---
 drivers/staging/vt6655/device_main.c | 1 -
 1 file changed, 1 deletion(-)

diff --git a/drivers/staging/vt6655/device_main.c b/drivers/staging/vt6655/device_main.c
index 21d10d9fde47..c8cae6df7f51 100644
--- a/drivers/staging/vt6655/device_main.c
+++ b/drivers/staging/vt6655/device_main.c
@@ -839,7 +839,6 @@ static int device_rx_srv(struct vnt_private *priv, unsigned int idx)
 				"can not allocate rx buf\n");
 			break;
 		}
-		rd->rd0.owner = OWNED_BY_NIC;
 	}
 
 	priv->pCurrRD[idx] = rd;
-- 
2.25.1

[RFC PATCH v2 4/4] staging: vt6655: implement allocation failure handling

[Nam Cao]

The function device_rx_srv does not handle allocation failure very well.
Currently, it performs these steps:
        - Unmap DMA buffer and hand over the buffer to mac80211
        - Allocate and dma-map new buffer
        - If allocation fails, abort

The problem is that, it aborts while still marking the buffer as
OWNED_BY_HOST. So when this function is called again in the future, it
incorrectly perceives the same buffer as valid and dma-unmap and hand
over this buffer to mac80211 again.

Re-implement this function to do things in a different order:
        - Allocate and dma-map new buffer
        - If allocation fails, abort and give up the ownership of the
          buffer (so that the device can re-use this buffer)
        - If allocation does not fail: unmap dma buffer and hand over
          the buffer to mac80211

Thus, when the driver cannot allocate new buffer, it simply discards the
received data and re-use the current buffer.

Also split device_alloc_rx_buf() into 2 parts: allocating new buffer and
initializing the buffer, so that we can read the old buffer in between.

Signed-off-by: Nam Cao <namcaov@gmail.com>
---
 drivers/staging/vt6655/device_main.c | 33 ++++++++++++++++++----------
 1 file changed, 21 insertions(+), 12 deletions(-)

diff --git a/drivers/staging/vt6655/device_main.c b/drivers/staging/vt6655/device_main.c
index c8cae6df7f51..cc952acd9825 100644
--- a/drivers/staging/vt6655/device_main.c
+++ b/drivers/staging/vt6655/device_main.c
@@ -132,7 +132,8 @@ static int device_init_td1_ring(struct vnt_private *priv);
 
 static int  device_rx_srv(struct vnt_private *priv, unsigned int idx);
 static int  device_tx_srv(struct vnt_private *priv, unsigned int idx);
-static bool device_alloc_rx_buf(struct vnt_private *, struct vnt_rx_desc *);
+static bool device_alloc_rx_buf(struct vnt_private *, struct vnt_rd_info *);
+static void device_init_rx_desc(struct vnt_private *priv, struct vnt_rx_desc *rd);
 static void device_free_rx_buf(struct vnt_private *priv,
 			       struct vnt_rx_desc *rd);
 static void device_init_registers(struct vnt_private *priv);
@@ -611,12 +612,13 @@ static int device_init_rd0_ring(struct vnt_private *priv)
 			goto err_free_desc;
 		}
 
-		if (!device_alloc_rx_buf(priv, desc)) {
+		if (!device_alloc_rx_buf(priv, desc->rd_info)) {
 			dev_err(&priv->pcid->dev, "can not alloc rx bufs\n");
 			ret = -ENOMEM;
 			goto err_free_rd;
 		}
 
+		device_init_rx_desc(priv, desc);
 		desc->next = &priv->aRD0Ring[(i + 1) % priv->opts.rx_descs0];
 		desc->next_desc = cpu_to_le32(curr + sizeof(struct vnt_rx_desc));
 	}
@@ -657,12 +659,13 @@ static int device_init_rd1_ring(struct vnt_private *priv)
 			goto err_free_desc;
 		}
 
-		if (!device_alloc_rx_buf(priv, desc)) {
+		if (!device_alloc_rx_buf(priv, desc->rd_info)) {
 			dev_err(&priv->pcid->dev, "can not alloc rx bufs\n");
 			ret = -ENOMEM;
 			goto err_free_rd;
 		}
 
+		device_init_rx_desc(priv, desc);
 		desc->next = &priv->aRD1Ring[(i + 1) % priv->opts.rx_descs1];
 		desc->next_desc = cpu_to_le32(curr + sizeof(struct vnt_rx_desc));
 	}
@@ -821,6 +824,7 @@ static void device_free_td1_ring(struct vnt_private *priv)
 static int device_rx_srv(struct vnt_private *priv, unsigned int idx)
 {
 	struct vnt_rx_desc *rd;
+	struct vnt_rd_info new_info;
 	int works = 0;
 
 	for (rd = priv->pCurrRD[idx];
@@ -832,13 +836,18 @@ static int device_rx_srv(struct vnt_private *priv, unsigned int idx)
 		if (!rd->rd_info->skb)
 			break;
 
-		vnt_receive_frame(priv, rd);
-
-		if (!device_alloc_rx_buf(priv, rd)) {
+		if (!device_alloc_rx_buf(priv, &new_info)) {
 			dev_err(&priv->pcid->dev,
 				"can not allocate rx buf\n");
+			rd->rd0.owner = OWNED_BY_NIC;
+			rd = rd->next;
 			break;
 		}
+
+		vnt_receive_frame(priv, rd);
+
+		memcpy(rd->rd_info, &new_info, sizeof(new_info));
+		device_init_rx_desc(priv, rd);
 	}
 
 	priv->pCurrRD[idx] = rd;
@@ -847,10 +856,8 @@ static int device_rx_srv(struct vnt_private *priv, unsigned int idx)
 }
 
 static bool device_alloc_rx_buf(struct vnt_private *priv,
-				struct vnt_rx_desc *rd)
+				struct vnt_rd_info *rd_info)
 {
-	struct vnt_rd_info *rd_info = rd->rd_info;
-
 	rd_info->skb = dev_alloc_skb((int)priv->rx_buf_sz);
 	if (!rd_info->skb)
 		return false;
@@ -864,15 +871,17 @@ static bool device_alloc_rx_buf(struct vnt_private *priv,
 		rd_info->skb = NULL;
 		return false;
 	}
+	return true;
+}
 
+static void device_init_rx_desc(struct vnt_private *priv, struct vnt_rx_desc *rd)
+{
 	*((unsigned int *)&rd->rd0) = 0; /* FIX cast */
 
 	rd->rd0.res_count = cpu_to_le16(priv->rx_buf_sz);
 	rd->rd0.owner = OWNED_BY_NIC;
 	rd->rd1.req_count = cpu_to_le16(priv->rx_buf_sz);
-	rd->buff_addr = cpu_to_le32(rd_info->skb_dma);
-
-	return true;
+	rd->buff_addr = cpu_to_le32(rd->rd_info->skb_dma);
 }
 
 static void device_free_rx_buf(struct vnt_private *priv,
-- 
2.25.1

Re: [RFC PATCH v2 0/4] staging: vt6655: Implement allocation failure handling

[Philipp Hortmann]

On 9/28/22 19:21, Nam Cao wrote:
> This driver does not handle allocation failure when receiving data very
> well. This patchset implements better handling in the case of allocation
> failure.
> 
> Also do some necessary clean-up to implement this.
> 
> v2:
>    - squash 3 commits that were doing a single thing
>    - add new commit which removes a redundant assignment
>    - take device_init_rx_desc() out of unnecessary else condition.
>    - remove return statement at the end of void function
>    - add a missing rd = rd->next statement in device_rx_srv(): because
>      we already drop the current buffer, we should move on to the next
>      buffer in the ring where new data will be written to.
> 
> Nam Cao (4):
>    staging: vt6655: remove redundant if condition
>    staging: vt6655: change vnt_receive_frame return type to void
>    staging: vt6655: remove redundant assignment
>    staging: vt6655: implement allocation failure handling
> 
>   drivers/staging/vt6655/device_main.c | 40 +++++++++++++++++-----------
>   drivers/staging/vt6655/dpc.c         |  8 +++---
>   drivers/staging/vt6655/dpc.h         |  2 +-
>   3 files changed, 28 insertions(+), 22 deletions(-)
> 

Tested-by: Philipp Hortmann <philipp.g.hortmann@gmail.com>