linux-kernel - [PATCH 3.2 047/110] stmmac: troubleshoot unexpected bits in des0 & des1

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Date:	Mon, 10 Aug 2015 12:12:31 +0200
From:	Ben Hutchings <ben@...adent.org.uk>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:	akpm@...ux-foundation.org,
	"Alexey Brodkin" <abrodkin@...opsys.com>,
	"David Miller" <davem@...emloft.net>, arc-linux-dev@...opsys.com,
	"Giuseppe Cavallaro" <peppe.cavallaro@...com>,
	"Alexey Brodkin" <Alexey.Brodkin@...opsys.com>
Subject: [PATCH 3.2 047/110] stmmac: troubleshoot unexpected bits in des0
 & des1

3.2.71-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Alexey Brodkin <Alexey.Brodkin@...opsys.com>

commit f1590670ce069eefeb93916391a67643e6ad1630 upstream.

Current implementation of descriptor init procedure only takes
care about setting/clearing ownership flag in "des0"/"des1"
fields while it is perfectly possible to get unexpected bits
set because of the following factors:

 [1] On driver probe underlying memory allocated with
     dma_alloc_coherent() might not be zeroed and so
     it will be filled with garbage.

 [2] During driver operation some bits could be set by SD/MMC
     controller (for example error flags etc).

And unexpected and/or randomly set flags in "des0"/"des1"
fields may lead to unpredictable behavior of GMAC DMA block.

This change addresses both items above with:

 [1] Use of dma_zalloc_coherent() instead of simple
     dma_alloc_coherent() to make sure allocated memory is
     zeroed. That shouldn't affect performance because
     this allocation only happens once on driver probe.

 [2] Do explicit zeroing of both "des0" and "des1" fields
     of all buffer descriptors during initialization of
     DMA transfer.

And while at it fixed identation of dma_free_coherent()
counterpart as well.

Signed-off-by: Alexey Brodkin <abrodkin@...opsys.com>
Cc: Giuseppe Cavallaro <peppe.cavallaro@...com>
Cc: arc-linux-dev@...opsys.com
Cc: linux-kernel@...r.kernel.org
Cc: David Miller <davem@...emloft.net>
Signed-off-by: David S. Miller <davem@...emloft.net>
[bwh: Backported to 3.2:
 - Adjust context, indentation
 - Normal and extended descriptors are allocated in the same place here]
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
--- a/drivers/net/ethernet/stmicro/stmmac/descs.h
+++ b/drivers/net/ethernet/stmicro/stmmac/descs.h
@@ -153,6 +153,8 @@ struct dma_desc {
 			u32 buffer2_size:13;
 			u32 reserved4:3;
 		} etx;		/* -- enhanced -- */
+
+		u64 all_flags;
 	} des01;
 	unsigned int des2;
 	unsigned int des3;
--- a/drivers/net/ethernet/stmicro/stmmac/enh_desc.c
+++ b/drivers/net/ethernet/stmicro/stmmac/enh_desc.c
@@ -232,6 +232,7 @@ static void enh_desc_init_rx_desc(struct
 {
 	int i;
 	for (i = 0; i < ring_size; i++) {
+		p->des01.all_flags = 0;
 		p->des01.erx.own = 1;
 		p->des01.erx.buffer1_size = BUF_SIZE_8KiB - 1;
 
@@ -248,7 +249,7 @@ static void enh_desc_init_tx_desc(struct
 	int i;
 
 	for (i = 0; i < ring_size; i++) {
-		p->des01.etx.own = 0;
+		p->des01.all_flags = 0;
 		ehn_desc_tx_set_on_ring_chain(p, (i == ring_size - 1));
 		p++;
 	}
--- a/drivers/net/ethernet/stmicro/stmmac/norm_desc.c
+++ b/drivers/net/ethernet/stmicro/stmmac/norm_desc.c
@@ -126,6 +126,7 @@ static void ndesc_init_rx_desc(struct dm
 {
 	int i;
 	for (i = 0; i < ring_size; i++) {
+		p->des01.all_flags = 0;
 		p->des01.rx.own = 1;
 		p->des01.rx.buffer1_size = BUF_SIZE_2KiB - 1;
 
@@ -141,7 +142,7 @@ static void ndesc_init_tx_desc(struct dm
 {
 	int i;
 	for (i = 0; i < ring_size; i++) {
-		p->des01.tx.own = 0;
+		p->des01.all_flags = 0;
 		ndesc_tx_set_on_ring_chain(p, (i == (ring_size - 1)));
 		p++;
 	}
--- a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
+++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
@@ -441,19 +441,17 @@ static void init_dma_desc_rings(struct n
 	priv->rx_skbuff =
 	    kmalloc(sizeof(struct sk_buff *) * rxsize, GFP_KERNEL);
 	priv->dma_rx =
-	    (struct dma_desc *)dma_alloc_coherent(priv->device,
-						  rxsize *
-						  sizeof(struct dma_desc),
-						  &priv->dma_rx_phy,
-						  GFP_KERNEL);
+	    (struct dma_desc *)dma_zalloc_coherent(priv->device, rxsize *
+						   sizeof(struct dma_desc),
+						   &priv->dma_rx_phy,
+						   GFP_KERNEL);
 	priv->tx_skbuff = kmalloc(sizeof(struct sk_buff *) * txsize,
 				       GFP_KERNEL);
 	priv->dma_tx =
-	    (struct dma_desc *)dma_alloc_coherent(priv->device,
-						  txsize *
-						  sizeof(struct dma_desc),
-						  &priv->dma_tx_phy,
-						  GFP_KERNEL);
+	    (struct dma_desc *)dma_zalloc_coherent(priv->device, txsize *
+						   sizeof(struct dma_desc),
+						   &priv->dma_tx_phy,
+						   GFP_KERNEL);
 
 	if ((priv->dma_rx == NULL) || (priv->dma_tx == NULL)) {
 		pr_err("%s:ERROR allocating the DMA Tx/Rx desc\n", __func__);

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