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Summary: The hardware does not expose a classic SMBus interface. Instead it has a lower level interface that can express a far richer I2C protocol than what smbus offers. However, the interface does not provide a way to explicitly generate the I2C stop and start conditions. It's only possible to request that the stop condition is generated after transferring the next byte in either direction. So, at least one data byte must always be transferred. Thus, some I2C sequences are impossible to generate, e.g., an equivalent of smbus quick command (<start>-<slave addr>-<r/w bit>-<stop>). At the same time isl(4) and cyapa(4) are moved to iicbus and now they use iicbus_transfer for communication. Previously they used smbus_trans() interface that is not defined by the SMBus protocol and was implemented only by ig4(4). In fact, that interface was impossible to implement for the typical SMBus controllers like intpm(4) or ichsmb(4) where a type of the SMBus command must be programmed. The plan is to remove smbus_trans() and all its uses. As an aside, the smbus_trans() method deviates from the standard, but perhaps backwards, FreeBSD convention of using 8-bit slave addresses (shifted by 1 bit to the left). The method expects 7-bit addresses. There is a user facing consequence of this change. A user must now provide device hints for isl and cyapa that specify an iicbus to use and a slave address on it. On Chromebook hardware where isl and cyapa devices are commonly found it is also possible to use a new chromebook_platform(4) driver that automatically configures isl and cyapa devices. There is no need to provide the device hints in that case, Right now smbus(4) driver tries to discover all slaves on the bus. That is very dangerous. Fortunately, the probing code uses smbus_trans() to do its job, so it is really enabled for ig4 only. The plan is to remove that auto-probing code and smbus_trans(). Tested by: grembo, Matthias Apitz <guru@unixarea.de> (w/o chromebook_platform) Discussed with: grembo, imp Reviewed by: wblock (docs) MFC after: 1 month Relnotes: yes Differential Revision: https://reviews.freebsd.org/D8172
83 lines
2.7 KiB
Groff
83 lines
2.7 KiB
Groff
.\" Copyright (c) 2015 Michael Gmelin <freebsd@grem.de>
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.\" All rights reserved.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" $FreeBSD$
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.\"
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.Dd October 03, 2016
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.Dt IG4 4
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.Os
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.Sh NAME
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.Nm ig4
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.Nd Intel(R) fourth generation mobile CPU integrated I2C driver
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.Sh SYNOPSIS
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To compile this driver into the kernel, place the following lines into
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the kernel configuration file:
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.Bd -ragged -offset indent
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.Cd "device ig4"
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.Cd "device iicbus"
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.Ed
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.Pp
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Alternatively, to load the driver as a module at boot time, place the following line in
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.Xr loader.conf 5 :
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.Bd -literal -offset indent
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ig4_load="YES"
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.Ed
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.Sh DESCRIPTION
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The
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.Nm
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driver provides access to peripherals attached to an I2C controller.
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.Sh HARDWARE
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.Nm
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supports the I2C controllers found in fourth generation Intel(R) Core(TM)
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processors based on the mobile U-processor line for intelligent systems.
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This includes the i7-4650U, i5-4300U, i3-4010U, and 2980U.
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.Sh SYSCTL VARIABLES
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These
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.Xr sysctl 8
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variables are available:
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.Bl -tag -width "debug.ig4_dump"
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.It Va debug.ig4_dump
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This sysctl is a zero-based bit mask.
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When any of the bits are set, a register dump is printed for
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every I2C transfer on an
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.Nm
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device with the same unit number.
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.El
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.Sh SEE ALSO
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.Xr iic 4 ,
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.Xr iicbus 4
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.Sh AUTHORS
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.An -nosplit
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The
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.Nm
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driver was written for DragonFly BSD by
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.An Matthew Dillon
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and subsequently ported to
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.Fx
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by
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.An Michael Gmelin Aq Mt freebsd@grem.de .
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.Pp
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This manual page was written by
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.An Michael Gmelin Aq Mt freebsd@grem.de .
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