From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753067AbdEHVoa (ORCPT ); Mon, 8 May 2017 17:44:30 -0400 Received: from bh-25.webhostbox.net ([208.91.199.152]:50795 "EHLO bh-25.webhostbox.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750835AbdEHVo2 (ORCPT ); Mon, 8 May 2017 17:44:28 -0400 Date: Mon, 8 May 2017 14:44:25 -0700 From: Guenter Roeck To: Dmitry Torokhov Cc: linux-input@vger.kernel.org, KT Liao , linux-kernel@vger.kernel.org Subject: Re: [PATCH] Input: elan_i2c - check if device is there before really probing Message-ID: <20170508214425.GA27206@roeck-us.net> References: <20170504062938.GA30771@dtor-ws> <20170508211031.GA31381@dtor-ws> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170508211031.GA31381@dtor-ws> User-Agent: Mutt/1.5.24 (2015-08-30) X-Authenticated_sender: guenter@roeck-us.net X-OutGoing-Spam-Status: No, score=-1.0 X-AntiAbuse: This header was added to track abuse, please include it with any abuse report X-AntiAbuse: Primary Hostname - bh-25.webhostbox.net X-AntiAbuse: Original Domain - vger.kernel.org X-AntiAbuse: Originator/Caller UID/GID - [47 12] / [47 12] X-AntiAbuse: Sender Address Domain - roeck-us.net X-Get-Message-Sender-Via: bh-25.webhostbox.net: authenticated_id: guenter@roeck-us.net X-Authenticated-Sender: bh-25.webhostbox.net: guenter@roeck-us.net X-Source: X-Source-Args: X-Source-Dir: Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, May 08, 2017 at 02:10:31PM -0700, Dmitry Torokhov wrote: > On Wed, May 03, 2017 at 11:42:54PM -0700, Guenter Roeck wrote: > > On 05/03/2017 11:29 PM, Dmitry Torokhov wrote: > > >Before trying to properly initialize the touchpad and generate bunch of > > >errors, let's first see it there is anything at the given address. If we > > >get error, fail silently with -ENXIO. > > > > > >Signed-off-by: Dmitry Torokhov > > >--- > > > drivers/input/mouse/elan_i2c_core.c | 9 +++++++++ > > > 1 file changed, 9 insertions(+) > > > > > >diff --git a/drivers/input/mouse/elan_i2c_core.c b/drivers/input/mouse/elan_i2c_core.c > > >index 5d3b53dd2fa2..0479730e7c5c 100644 > > >--- a/drivers/input/mouse/elan_i2c_core.c > > >+++ b/drivers/input/mouse/elan_i2c_core.c > > >@@ -1040,6 +1040,7 @@ static int elan_probe(struct i2c_client *client, > > > const struct elan_transport_ops *transport_ops; > > > struct device *dev = &client->dev; > > > struct elan_tp_data *data; > > >+ union i2c_smbus_data dummy; > > > unsigned long irqflags; > > > int error; > > > > > >@@ -1091,6 +1092,14 @@ static int elan_probe(struct i2c_client *client, > > > return error; > > > } > > > > > >+ /* Make sure there is something at this address */ > > >+ error = i2c_smbus_xfer(client->adapter, client->addr, 0, > > >+ I2C_SMBUS_READ, 0, I2C_SMBUS_BYTE, &dummy); > > > > Can't you just call i2c_smbus_read_byte_data(client, 0); and check if it returns > > an error ? > > Are we guaranteed to get a result from command "0"? I am not sure, and > looking at least at i2c_smbus_xfer_emulated() I2C_SMBUS_READ with > I2C_SMBUS_BYTE modifier works differently form > I2C_SMBUS_READ/I2C_SMBUS_BYTE_DATA (the former uses a single i2c message > vs 2 for the latter). > > Also the form above is what i2c core uses to do detection when adapter > does not implement I2C_SMBUS_QUICK, so I'd rather leave it as it was. > How about i2c_smbus_read_byte() ? status = i2c_smbus_xfer(client->adapter, client->addr, client->flags, I2C_SMBUS_READ, 0, I2C_SMBUS_BYTE, &data); return (status < 0) ? status : data.byte; Guenter