Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932241AbcDYLvd (ORCPT ); Mon, 25 Apr 2016 07:51:33 -0400 Received: from mga14.intel.com ([192.55.52.115]:40217 "EHLO mga14.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932118AbcDYLvb (ORCPT ); Mon, 25 Apr 2016 07:51:31 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.24,532,1455004800"; d="scan'208";a="965931327" Subject: Re: [PATCH] i2c: designware: do not disable adapter after transfer To: Lucas De Marchi , "linux-i2c@vger.kernel.org" References: <5707B9B4.6020402@alitech.com> <1461337687-2484-1-git-send-email-lucas.demarchi@intel.com> Cc: "wsa@the-dreams.de" , "linux-kernel@vger.kernel.org" , "mika.westerberg@linux.intel.com" From: Jarkko Nikula Message-ID: <571E04BA.3030301@linux.intel.com> Date: Mon, 25 Apr 2016 14:51:22 +0300 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Icedove/38.6.0 MIME-Version: 1.0 In-Reply-To: <1461337687-2484-1-git-send-email-lucas.demarchi@intel.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2434 Lines: 69 On 04/22/2016 06:08 PM, Lucas De Marchi wrote: > Disabling the adapter after each transfer is pretty bad for sensors and > other devices doing small transfers at a high rate. It slows down the > transfer rate a lot since each of them have to wait the adapter to be > enabled again. > > During the transfer init we check the status register for no activity > and TX buffer being empty since otherwise we can't change IC_TAR > dynamically. > > When a transfer fails the adapter will still be disabled - this is a > conservative approach. When transfers succeed, the adapter is left > enabled and it's configured so to disable interrupts. > > With a small program test to read/write registers in a sensor the speed > doubled. Example below with write sequences of 16 bytes: > > Before: > i2c-transfer-time -w -a 0x40 -x 6 -n 20000 -- 0 0 0xd0 0x07 0 0 0xd0 0x07 0 0 0xd0 0x07 0 0 0xd0 0x07 > num_transfers=20000 > transfer_time_avg=1032.728500us > > After: > i2c-transfer-time -w -a 0x40 -x 6 -n 20000 -- 0 0 0xd0 0x07 0 0 0xd0 0x07 0 0 0xd0 0x07 0 0 0xd0 0x07 > num_transfers=20000 > transfer_time_avg=470.256050us > > Signed-off-by: Lucas De Marchi > --- > drivers/i2c/busses/i2c-designware-core.c | 48 ++++++++++++++++++++------------ > drivers/i2c/busses/i2c-designware-core.h | 1 + > 2 files changed, 31 insertions(+), 18 deletions(-) > > diff --git a/drivers/i2c/busses/i2c-designware-core.c b/drivers/i2c/busses/i2c-designware-core.c > index 99b54be..8a08e68 100644 > --- a/drivers/i2c/busses/i2c-designware-core.c > +++ b/drivers/i2c/busses/i2c-designware-core.c > @@ -90,6 +90,7 @@ > DW_IC_INTR_STOP_DET) > > #define DW_IC_STATUS_ACTIVITY 0x1 > +#define DW_IC_STATUS_TX_EMPTY 0x2 ... > @@ -413,8 +416,16 @@ static void i2c_dw_xfer_init(struct dw_i2c_dev *dev) > struct i2c_msg *msgs = dev->msgs; > u32 ic_con, ic_tar = 0; > > - /* Disable the adapter */ > - __i2c_dw_enable(dev, false); > + if (dev->enabled) { > + u32 ic_status; > + > + /* check ic_tar and ic_con can be dynamically updated */ > + ic_status = dw_readl(dev, DW_IC_STATUS); > + if (ic_status & DW_IC_STATUS_ACTIVITY > + || !(ic_status & DW_IC_STATUS_TX_EMPTY)) { > + __i2c_dw_enable(dev, false); > + } > + } > Worth to double check this. I see bit 1 means TX FIFO not full and bit 2 is TX FIFO completely empty. Otherwise I'm fine with the patch as long as it works for Christian. -- Jarkko