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enc28j60: reduce the number of spi transfers in enc28j60_set_bank()

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A major source of overhead in the enc28j60 driver is the SPI transfers. Each
SPI transfer entails two kernel thread context switches. One major source of
SPI transfers is the enc28j60_set_bank() functions which runs before every
register access. This patch reduces the number of SPI transfers that
enc28j60_set_bank() performs in two ways:

  1. removes unnecessary bank switch for the registers that are present in all
	 banks

  2. when switching from banks 0 or 3 to banks 1 or 2 (i.e. only one bit
	 changes) enc28j60_set_bank() does only one SPI transfer instead of two

According to my tests these changes reduce the number of SPI transfers in
about 25%.

Signed-off-by: Baruch Siach <baruch@tkos.co.il>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Baruch Siach 2008-12-18 19:39:14 -08:00 committed by David S. Miller
parent b88a2a22c6
commit 5664dd5561
1 changed files with 23 additions and 7 deletions
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30
drivers/net/enc28j60.c
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@ -196,16 +196,32 @@ static void enc28j60_soft_reset(struct enc28j60_net *priv)
*/
static void enc28j60_set_bank(struct enc28j60_net *priv, u8 addr)
{
if ((addr & BANK_MASK) != priv->bank) {
u8 b = (addr & BANK_MASK) >> 5;
u8 b = (addr & BANK_MASK) >> 5;
if (b != (ECON1_BSEL1 | ECON1_BSEL0))
/* These registers (EIE, EIR, ESTAT, ECON2, ECON1)
* are present in all banks, no need to switch bank
*/
if (addr >= EIE && addr <= ECON1)
return;
/* Clear or set each bank selection bit as needed */
if ((b & ECON1_BSEL0) != (priv->bank & ECON1_BSEL0)) {
if (b & ECON1_BSEL0)
spi_write_op(priv, ENC28J60_BIT_FIELD_SET, ECON1,
ECON1_BSEL0);
else
spi_write_op(priv, ENC28J60_BIT_FIELD_CLR, ECON1,
ECON1_BSEL1 | ECON1_BSEL0);
if (b != 0)
spi_write_op(priv, ENC28J60_BIT_FIELD_SET, ECON1, b);
priv->bank = (addr & BANK_MASK);
ECON1_BSEL0);
}
if ((b & ECON1_BSEL1) != (priv->bank & ECON1_BSEL1)) {
if (b & ECON1_BSEL1)
spi_write_op(priv, ENC28J60_BIT_FIELD_SET, ECON1,
ECON1_BSEL1);
else
spi_write_op(priv, ENC28J60_BIT_FIELD_CLR, ECON1,
ECON1_BSEL1);
}
priv->bank = b;
}
/*