From: Baruch Siach Subject: [PATCH] enc28j60: reduce the number of spi transfers in enc28j60_set_bank() Date: Thu, 18 Dec 2008 09:57:32 +0200 Message-ID: <20081218075732.GA1880@diamond.tkos.co.il> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: netdev@vger.kernel.org To: Claudio Lanconelli Return-path: Received: from tango.tkos.co.il ([62.219.50.35]:58548 "EHLO tango.tkos.co.il" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750888AbYLRH5u (ORCPT ); Thu, 18 Dec 2008 02:57:50 -0500 Content-Disposition: inline Sender: netdev-owner@vger.kernel.org List-ID: 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 --- --- drivers/net/enc28j60.c-git 2008-12-18 09:29:49.000000000 +0200 +++ drivers/net/enc28j60.c 2008-12-18 09:33:14.000000000 +0200 @@ -196,16 +196,32 @@ static void enc28j60_soft_reset(struct e */ 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_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 | ECON1_BSEL0); - if (b != 0) - spi_write_op(priv, ENC28J60_BIT_FIELD_SET, ECON1, b); - priv->bank = (addr & BANK_MASK); + ECON1_BSEL1); } + priv->bank = b; } /* -- ~. .~ Tk Open Systems =}------------------------------------------------ooO--U--Ooo------------{= - baruch@tkos.co.il - tel: +972.2.679.5364, http://www.tkos.co.il -