[PATCH v2] stmmac: troubleshoot unexpected bits in des0 & des1

Alexey Brodkin
2015-06-24T08:07:54Z

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.

Signed-off-by: Alexey Brodkin <abrodkin@synopsys.com>
Cc: Giuseppe Cavallaro <peppe.cavallaro@st.com>
Cc: arc-linux-dev@synopsys.com
Cc: linux-kernel@vger.kernel.org
Cc: stable@vger.kernel.org
Cc: David Miller <davem@davemloft.net>
---
drivers/net/ethernet/stmicro/stmmac/descs.h | 2 ++
drivers/net/ethernet/stmicro/stmmac/enh_desc.c | 3 ++-
drivers/net/ethernet/stmicro/stmmac/norm_desc.c | 3 ++-
drivers/net/ethernet/stmicro/stmmac/stmmac_main.c | 8 ++++----
4 files changed, 10 insertions(+), 6 deletions(-)

diff --git a/drivers/net/ethernet/stmicro/stmmac/descs.h b/drivers/net/ethernet/stmicro/stmmac/descs.h
index ad39960..799c292 100644
--- a/drivers/net/ethernet/stmicro/stmmac/descs.h
+++ b/drivers/net/ethernet/stmicro/stmmac/descs.h
@@ -158,6 +158,8 @@ struct dma_desc {
u32 buffer2_size:13;
u32 reserved4:3;
} etx; /* -- enhanced -- */
+
+ u64 all_flags;
} des01;
unsigned int des2;
unsigned int des3;
diff --git a/drivers/net/ethernet/stmicro/stmmac/enh_desc.c b/drivers/net/ethernet/stmicro/stmmac/enh_desc.c
index 1e2bcf5..7d94444 100644
--- a/drivers/net/ethernet/stmicro/stmmac/enh_desc.c
+++ b/drivers/net/ethernet/stmicro/stmmac/enh_desc.c
@@ -240,6 +240,7 @@ static int enh_desc_get_rx_status(void *data, struct stmmac_extra_stats *x,
static void enh_desc_init_rx_desc(struct dma_desc *p, int disable_rx_ic,
int mode, int end)
{
+ p->des01.all_flags = 0;
p->des01.erx.own = 1;
p->des01.erx.buffer1_size = BUF_SIZE_8KiB - 1;

@@ -254,7 +255,7 @@ static void enh_desc_init_rx_desc(struct dma_desc *p, int disable_rx_ic,

static void enh_desc_init_tx_desc(struct dma_desc *p, int mode, int end)
{
- p->des01.etx.own = 0;
+ p->des01.all_flags = 0;
if (mode == STMMAC_CHAIN_MODE)
ehn_desc_tx_set_on_chain(p, end);
else
diff --git a/drivers/net/ethernet/stmicro/stmmac/norm_desc.c b/drivers/net/ethernet/stmicro/stmmac/norm_desc.c
index 35ad4f4..48c3456 100644
--- a/drivers/net/ethernet/stmicro/stmmac/norm_desc.c
+++ b/drivers/net/ethernet/stmicro/stmmac/norm_desc.c
@@ -123,6 +123,7 @@ static int ndesc_get_rx_status(void *data, struct stmmac_extra_stats *x,
static void ndesc_init_rx_desc(struct dma_desc *p, int disable_rx_ic, int mode,
int end)
{
+ p->des01.all_flags = 0;
p->des01.rx.own = 1;
p->des01.rx.buffer1_size = BUF_SIZE_2KiB - 1;

@@ -137,7 +138,7 @@ static void ndesc_init_rx_desc(struct dma_desc *p, int disable_rx_ic, int mode,

static void ndesc_init_tx_desc(struct dma_desc *p, int mode, int end)
{
- p->des01.tx.own = 0;
+ p->des01.all_flags = 0;
if (mode == STMMAC_CHAIN_MODE)
ndesc_tx_set_on_chain(p, end);
else
diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
index 18c46bb..3309b98 100644
--- a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
+++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
@@ -1172,7 +1172,7 @@ static int alloc_dma_desc_resources(struct stmmac_priv *priv)
goto err_tx_skbuff;

if (priv->extend_desc) {
- priv->dma_erx = dma_alloc_coherent(priv->device, rxsize *
+ priv->dma_erx = dma_zalloc_coherent(priv->device, rxsize *
sizeof(struct
dma_extended_desc),
&priv->dma_rx_phy,
@@ -1180,7 +1180,7 @@ static int alloc_dma_desc_resources(struct stmmac_priv *priv)
if (!priv->dma_erx)
goto err_dma;

- priv->dma_etx = dma_alloc_coherent(priv->device, txsize *
+ priv->dma_etx = dma_zalloc_coherent(priv->device, txsize *
sizeof(struct
dma_extended_desc),
&priv->dma_tx_phy,
@@ -1192,14 +1192,14 @@ static int alloc_dma_desc_resources(struct stmmac_priv *priv)
goto err_dma;
}
} else {
- priv->dma_rx = dma_alloc_coherent(priv->device, rxsize *
+ priv->dma_rx = dma_zalloc_coherent(priv->device, rxsize *
sizeof(struct dma_desc),
&priv->dma_rx_phy,
GFP_KERNEL);
if (!priv->dma_rx)
goto err_dma;

- priv->dma_tx = dma_alloc_coherent(priv->device, txsize *
+ priv->dma_tx = dma_zalloc_coherent(priv->device, txsize *
sizeof(struct dma_desc),
&priv->dma_tx_phy,
GFP_KERNEL);
--
2.4.2