On Thursday 17 November 2011 00:15:42 Michael Büsch wrote:
> On Thu, 17 Nov 2011 00:12:03 +0100
> Christian Lamparter <chunkeey@xxxxxxxxxxxxxx> wrote:
> > BTW: I always wondered if it would make sense to have a
> > cached rx skb ready in p54spi_rx(). This way we don't
> > have to do DMA onto the stack [which is really ugly and
> > possibly illegal] and might even get a better rx
> > performance. I could write the code but as you know I don't
> > have the hardware to test it.
>
> I'll test it, if you can come up with a patch.
---
[RFC] p54spi: don't DMA onto the stack
DMA transfers should not be done onto the kernel stack.
---
diff --git a/drivers/net/wireless/p54/p54spi.c b/drivers/net/wireless/p54/p54spi.c
index 2d5cf5b..b3b1ff7 100644
--- a/drivers/net/wireless/p54/p54spi.c
+++ b/drivers/net/wireless/p54/p54spi.c
@@ -339,22 +339,55 @@ static void p54spi_int_ready(struct p54s_priv *priv)
}
}
+static int p54spi_alloc_rx_skb(struct p54s_priv *priv)
+{
+ if (priv->rx_cache != NULL)
+ return 0;
+
+ /*
+ * Add extra space for spi rx header and reserve some space since the
+ * firmware may insert up to 4 padding bytes after the lmac header,
+ * but it does not amend the size of SPI data transfer. Such packets
+ * has correct data size in header, thus referencing past the end of
+ * allocated skb. Reserve extra 4 bytes for this case.
+ */
+#define RX_EXTRA_SPACE (sizeof(__le16) + sizeof(struct p54_rx_data) + 4)
+
+ priv->rx_cache = dev_alloc_skb(priv->common.rx_mtu + RX_EXTRA_SPACE);
+ if (!priv->rx_cache)
+ return -ENOMEM;
+
+ /* reserve head space for spi transfer length. */
+ skb_reserve(priv->rx_cache, 2);
+ return 0;
+}
+
static int p54spi_rx(struct p54s_priv *priv)
{
struct sk_buff *skb;
+ __le16 *rx_head;
+ int err;
u16 len;
- u16 rx_head[2];
-#define READAHEAD_SZ (sizeof(rx_head)-sizeof(u16))
+
+#define READAHEAD (sizeof(__le16))
if (p54spi_wakeup(priv) < 0)
return -EBUSY;
- /* Read data size and first data word in one SPI transaction
+ err = p54spi_alloc_rx_skb(priv);
+ if (err)
+ return err;
+
+ /*
+ * Read data size and first data word in one SPI transaction
* This is workaround for firmware/DMA bug,
* when first data word gets lost under high load.
*/
- p54spi_spi_read(priv, SPI_ADRS_DMA_DATA, rx_head, sizeof(rx_head));
- len = rx_head[0];
+ skb = priv->rx_cache;
+ rx_head = (__le16 *)(unsigned long)(priv->rx_cache->data -
+ sizeof(__le16));
+ p54spi_spi_read(priv, SPI_ADRS_DMA_DATA, rx_head, 4);
+ len = le16_to_cpu(rx_head[0]);
if (len == 0) {
p54spi_sleep(priv);
@@ -362,36 +395,41 @@ static int p54spi_rx(struct p54s_priv *priv)
return 0;
}
- /* Firmware may insert up to 4 padding bytes after the lmac header,
- * but it does not amend the size of SPI data transfer.
- * Such packets has correct data size in header, thus referencing
- * past the end of allocated skb. Reserve extra 4 bytes for this case */
- skb = dev_alloc_skb(len + 4);
- if (!skb) {
+ if (len >= (RX_EXTRA_SPACE + priv->common.rx_mtu)) {
p54spi_sleep(priv);
- dev_err(&priv->spi->dev, "could not alloc skb");
- return -ENOMEM;
+ dev_err(&priv->spi->dev, "rx request larger than max rx mtu\n");
+ return 0;
}
- if (len <= READAHEAD_SZ) {
- memcpy(skb_put(skb, len), rx_head + 1, len);
+ if (len <= READAHEAD) {
+ skb_put(skb, len);
} else {
- memcpy(skb_put(skb, READAHEAD_SZ), rx_head + 1, READAHEAD_SZ);
+ skb_put(skb, READAHEAD);
p54spi_spi_read(priv, SPI_ADRS_DMA_DATA,
- skb_put(skb, len - READAHEAD_SZ),
- len - READAHEAD_SZ);
+ skb_put(skb, len - READAHEAD),
+ len - READAHEAD);
}
p54spi_sleep(priv);
- /* Put additional bytes to compensate for the possible
- * alignment-caused truncation */
+ /*
+ * Put additional bytes to compensate for the possible
+ * alignment-caused truncation
+ */
skb_put(skb, 4);
- if (p54_rx(priv->hw, skb) == 0)
- dev_kfree_skb(skb);
+ if (p54_rx(priv->hw, skb) == 0) {
+ /* skb was not used up, can be recycled */
+ skb_reset_tail_pointer(skb);
+ skb_trim(skb, 0);
+ } else {
+ /* get next skb ready */
+ priv->rx_cache = NULL;
+ return p54spi_alloc_rx_skb(priv);
+ }
return 0;
}
-
+#undef RX_EXTRA_SPACE
+#undef READAHEAD
static irqreturn_t p54spi_interrupt(int irq, void *config)
{
@@ -666,6 +704,8 @@ static int __devinit p54spi_probe(struct spi_device *spi)
if (ret)
goto err_free_common;
+ p54spi_alloc_rx_skb(priv);
+
ret = p54_register_common(hw, &priv->spi->dev);
if (ret)
goto err_free_common;
@@ -691,6 +731,7 @@ static int __devexit p54spi_remove(struct spi_device *spi)
mutex_destroy(&priv->mutex);
+ kfree_skb(priv->rx_cache);
p54_free_common(priv->hw);
return 0;
diff --git a/drivers/net/wireless/p54/p54spi.h b/drivers/net/wireless/p54/p54spi.h
index dfaa62a..3e19d26 100644
--- a/drivers/net/wireless/p54/p54spi.h
+++ b/drivers/net/wireless/p54/p54spi.h
@@ -25,7 +25,7 @@
#include <linux/mutex.h>
#include <linux/list.h>
#include <net/mac80211.h>
-
+#include <linux/skbuff.h>
#include "p54.h"
/* Bit 15 is read/write bit; ON = READ, OFF = WRITE */
@@ -118,6 +118,8 @@ struct p54s_priv {
/* protected by tx_lock */
struct list_head tx_pending;
+ struct sk_buff *rx_cache;
+
enum fw_state fw_state;
const struct firmware *firmware;
};
--
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