diff options
Diffstat (limited to 'Documentation/i2c')
| -rw-r--r-- | Documentation/i2c/busses/i2c-piix4.rst | 13 | ||||
| -rw-r--r-- | Documentation/i2c/dev-interface.rst | 2 | ||||
| -rw-r--r-- | Documentation/i2c/i2c-topology.rst | 214 | ||||
| -rw-r--r-- | Documentation/i2c/slave-interface.rst | 6 | ||||
| -rw-r--r-- | Documentation/i2c/writing-clients.rst | 4 |
5 files changed, 126 insertions, 113 deletions
diff --git a/Documentation/i2c/busses/i2c-piix4.rst b/Documentation/i2c/busses/i2c-piix4.rst index cc9000259223..07fe6f6f4b18 100644 --- a/Documentation/i2c/busses/i2c-piix4.rst +++ b/Documentation/i2c/busses/i2c-piix4.rst @@ -64,7 +64,7 @@ correct address for this module, you could get in big trouble (read: crashes, data corruption, etc.). Try this only as a last resort (try BIOS updates first, for example), and backup first! An even more dangerous option is 'force_addr=<IOPORT>'. This will not only enable the PIIX4 like -'force' foes, but it will also set a new base I/O port address. The SMBus +'force' does, but it will also set a new base I/O port address. The SMBus parts of the PIIX4 needs a range of 8 of these addresses to function correctly. If these addresses are already reserved by some other device, you will get into big trouble! DON'T USE THIS IF YOU ARE NOT VERY SURE @@ -86,15 +86,15 @@ If you own Force CPCI735 motherboard or other OSB4 based systems you may need to change the SMBus Interrupt Select register so the SMBus controller uses the SMI mode. -1) Use lspci command and locate the PCI device with the SMBus controller: +1) Use ``lspci`` command and locate the PCI device with the SMBus controller: 00:0f.0 ISA bridge: ServerWorks OSB4 South Bridge (rev 4f) The line may vary for different chipsets. Please consult the driver source - for all possible PCI ids (and lspci -n to match them). Lets assume the + for all possible PCI ids (and ``lspci -n`` to match them). Let's assume the device is located at 00:0f.0. 2) Now you just need to change the value in 0xD2 register. Get it first with - command: lspci -xxx -s 00:0f.0 + command: ``lspci -xxx -s 00:0f.0`` If the value is 0x3 then you need to change it to 0x1: - setpci -s 00:0f.0 d2.b=1 + ``setpci -s 00:0f.0 d2.b=1`` Please note that you don't need to do that in all cases, just when the SMBus is not working properly. @@ -109,6 +109,3 @@ which can easily get corrupted due to a state machine bug. These are mostly Thinkpad laptops, but desktop systems may also be affected. We have no list of all affected systems, so the only safe solution was to prevent access to the SMBus on all IBM systems (detected using DMI data.) - -For additional information, read: -http://www.lm-sensors.org/browser/lm-sensors/trunk/README diff --git a/Documentation/i2c/dev-interface.rst b/Documentation/i2c/dev-interface.rst index 73ad34849f99..c277a8e1202b 100644 --- a/Documentation/i2c/dev-interface.rst +++ b/Documentation/i2c/dev-interface.rst @@ -148,7 +148,7 @@ You can do plain I2C transactions by using read(2) and write(2) calls. You do not need to pass the address byte; instead, set it through ioctl I2C_SLAVE before you try to access the device. -You can do SMBus level transactions (see documentation file smbus-protocol +You can do SMBus level transactions (see documentation file smbus-protocol.rst for details) through the following functions:: __s32 i2c_smbus_write_quick(int file, __u8 value); diff --git a/Documentation/i2c/i2c-topology.rst b/Documentation/i2c/i2c-topology.rst index 7cb53819778e..48fce0f7491b 100644 --- a/Documentation/i2c/i2c-topology.rst +++ b/Documentation/i2c/i2c-topology.rst @@ -5,6 +5,8 @@ I2C muxes and complex topologies There are a couple of reasons for building more complex I2C topologies than a straight-forward I2C bus with one adapter and one or more devices. +Some example use cases are: + 1. A mux may be needed on the bus to prevent address collisions. 2. The bus may be accessible from some external bus master, and arbitration @@ -14,10 +16,10 @@ than a straight-forward I2C bus with one adapter and one or more devices. from the I2C bus, at least most of the time, and sits behind a gate that has to be operated before the device can be accessed. -Etc -=== +Several types of hardware components such as I2C muxes, I2C gates and I2C +arbitrators allow to handle such needs. -These constructs are represented as I2C adapter trees by Linux, where +These components are represented as I2C adapter trees by Linux, where each adapter has a parent adapter (except the root adapter) and zero or more child adapters. The root adapter is the actual adapter that issues I2C transfers, and all adapters with a parent are part of an "i2c-mux" @@ -35,46 +37,7 @@ Locking ======= There are two variants of locking available to I2C muxes, they can be -mux-locked or parent-locked muxes. As is evident from below, it can be -useful to know if a mux is mux-locked or if it is parent-locked. The -following list was correct at the time of writing: - -In drivers/i2c/muxes/: - -====================== ============================================= -i2c-arb-gpio-challenge Parent-locked -i2c-mux-gpio Normally parent-locked, mux-locked iff - all involved gpio pins are controlled by the - same I2C root adapter that they mux. -i2c-mux-gpmux Normally parent-locked, mux-locked iff - specified in device-tree. -i2c-mux-ltc4306 Mux-locked -i2c-mux-mlxcpld Parent-locked -i2c-mux-pca9541 Parent-locked -i2c-mux-pca954x Parent-locked -i2c-mux-pinctrl Normally parent-locked, mux-locked iff - all involved pinctrl devices are controlled - by the same I2C root adapter that they mux. -i2c-mux-reg Parent-locked -====================== ============================================= - -In drivers/iio/: - -====================== ============================================= -gyro/mpu3050 Mux-locked -imu/inv_mpu6050/ Mux-locked -====================== ============================================= - -In drivers/media/: - -======================= ============================================= -dvb-frontends/lgdt3306a Mux-locked -dvb-frontends/m88ds3103 Parent-locked -dvb-frontends/rtl2830 Parent-locked -dvb-frontends/rtl2832 Mux-locked -dvb-frontends/si2168 Mux-locked -usb/cx231xx/ Parent-locked -======================= ============================================= +mux-locked or parent-locked muxes. Mux-locked muxes @@ -89,40 +52,8 @@ full transaction, unrelated I2C transfers may interleave the different stages of the transaction. This has the benefit that the mux driver may be easier and cleaner to implement, but it has some caveats. -==== ===================================================================== -ML1. If you build a topology with a mux-locked mux being the parent - of a parent-locked mux, this might break the expectation from the - parent-locked mux that the root adapter is locked during the - transaction. - -ML2. It is not safe to build arbitrary topologies with two (or more) - mux-locked muxes that are not siblings, when there are address - collisions between the devices on the child adapters of these - non-sibling muxes. - - I.e. the select-transfer-deselect transaction targeting e.g. device - address 0x42 behind mux-one may be interleaved with a similar - operation targeting device address 0x42 behind mux-two. The - intension with such a topology would in this hypothetical example - be that mux-one and mux-two should not be selected simultaneously, - but mux-locked muxes do not guarantee that in all topologies. - -ML3. A mux-locked mux cannot be used by a driver for auto-closing - gates/muxes, i.e. something that closes automatically after a given - number (one, in most cases) of I2C transfers. Unrelated I2C transfers - may creep in and close prematurely. - -ML4. If any non-I2C operation in the mux driver changes the I2C mux state, - the driver has to lock the root adapter during that operation. - Otherwise garbage may appear on the bus as seen from devices - behind the mux, when an unrelated I2C transfer is in flight during - the non-I2C mux-changing operation. -==== ===================================================================== - - Mux-locked Example ------------------- - +~~~~~~~~~~~~~~~~~~ :: @@ -153,6 +84,43 @@ This means that accesses to D2 are lockout out for the full duration of the entire operation. But accesses to D3 are possibly interleaved at any point. +Mux-locked caveats +~~~~~~~~~~~~~~~~~~ + +When using a mux-locked mux, be aware of the following restrictions: + +[ML1] + If you build a topology with a mux-locked mux being the parent + of a parent-locked mux, this might break the expectation from the + parent-locked mux that the root adapter is locked during the + transaction. + +[ML2] + It is not safe to build arbitrary topologies with two (or more) + mux-locked muxes that are not siblings, when there are address + collisions between the devices on the child adapters of these + non-sibling muxes. + + I.e. the select-transfer-deselect transaction targeting e.g. device + address 0x42 behind mux-one may be interleaved with a similar + operation targeting device address 0x42 behind mux-two. The + intent with such a topology would in this hypothetical example + be that mux-one and mux-two should not be selected simultaneously, + but mux-locked muxes do not guarantee that in all topologies. + +[ML3] + A mux-locked mux cannot be used by a driver for auto-closing + gates/muxes, i.e. something that closes automatically after a given + number (one, in most cases) of I2C transfers. Unrelated I2C transfers + may creep in and close prematurely. + +[ML4] + If any non-I2C operation in the mux driver changes the I2C mux state, + the driver has to lock the root adapter during that operation. + Otherwise garbage may appear on the bus as seen from devices + behind the mux, when an unrelated I2C transfer is in flight during + the non-I2C mux-changing operation. + Parent-locked muxes ------------------- @@ -161,28 +129,10 @@ Parent-locked muxes lock the parent adapter during the full select- transfer-deselect transaction. The implication is that the mux driver has to ensure that any and all I2C transfers through that parent adapter during the transaction are unlocked I2C transfers (using e.g. -__i2c_transfer), or a deadlock will follow. There are a couple of -caveats. - -==== ==================================================================== -PL1. If you build a topology with a parent-locked mux being the child - of another mux, this might break a possible assumption from the - child mux that the root adapter is unused between its select op - and the actual transfer (e.g. if the child mux is auto-closing - and the parent mux issues I2C transfers as part of its select). - This is especially the case if the parent mux is mux-locked, but - it may also happen if the parent mux is parent-locked. - -PL2. If select/deselect calls out to other subsystems such as gpio, - pinctrl, regmap or iio, it is essential that any I2C transfers - caused by these subsystems are unlocked. This can be convoluted to - accomplish, maybe even impossible if an acceptably clean solution - is sought. -==== ==================================================================== - +__i2c_transfer), or a deadlock will follow. Parent-locked Example ---------------------- +~~~~~~~~~~~~~~~~~~~~~ :: @@ -212,10 +162,30 @@ When there is an access to D1, this happens: 9. M1 unlocks its parent adapter. 10. M1 unlocks muxes on its parent. - This means that accesses to both D2 and D3 are locked out for the full duration of the entire operation. +Parent-locked Caveats +~~~~~~~~~~~~~~~~~~~~~ + +When using a parent-locked mux, be aware of the following restrictions: + +[PL1] + If you build a topology with a parent-locked mux being the child + of another mux, this might break a possible assumption from the + child mux that the root adapter is unused between its select op + and the actual transfer (e.g. if the child mux is auto-closing + and the parent mux issues I2C transfers as part of its select). + This is especially the case if the parent mux is mux-locked, but + it may also happen if the parent mux is parent-locked. + +[PL2] + If select/deselect calls out to other subsystems such as gpio, + pinctrl, regmap or iio, it is essential that any I2C transfers + caused by these subsystems are unlocked. This can be convoluted to + accomplish, maybe even impossible if an acceptably clean solution + is sought. + Complex Examples ================ @@ -261,8 +231,10 @@ This is a good topology:: When device D1 is accessed, accesses to D2 are locked out for the full duration of the operation (muxes on the top child adapter of M1 are locked). But accesses to D3 and D4 are possibly interleaved at -any point. Accesses to D3 locks out D1 and D2, but accesses to D4 -are still possibly interleaved. +any point. + +Accesses to D3 locks out D1 and D2, but accesses to D4 are still possibly +interleaved. Mux-locked mux as parent of parent-locked mux @@ -394,3 +366,47 @@ This is a good topology:: When D1 or D2 are accessed, accesses to D3 and D4 are locked out while accesses to D5 may interleave. When D3 or D4 are accessed, accesses to all other devices are locked out. + + +Mux type of existing device drivers +=================================== + +Whether a device is mux-locked or parent-locked depends on its +implementation. The following list was correct at the time of writing: + +In drivers/i2c/muxes/: + +====================== ============================================= +i2c-arb-gpio-challenge Parent-locked +i2c-mux-gpio Normally parent-locked, mux-locked iff + all involved gpio pins are controlled by the + same I2C root adapter that they mux. +i2c-mux-gpmux Normally parent-locked, mux-locked iff + specified in device-tree. +i2c-mux-ltc4306 Mux-locked +i2c-mux-mlxcpld Parent-locked +i2c-mux-pca9541 Parent-locked +i2c-mux-pca954x Parent-locked +i2c-mux-pinctrl Normally parent-locked, mux-locked iff + all involved pinctrl devices are controlled + by the same I2C root adapter that they mux. +i2c-mux-reg Parent-locked +====================== ============================================= + +In drivers/iio/: + +====================== ============================================= +gyro/mpu3050 Mux-locked +imu/inv_mpu6050/ Mux-locked +====================== ============================================= + +In drivers/media/: + +======================= ============================================= +dvb-frontends/lgdt3306a Mux-locked +dvb-frontends/m88ds3103 Parent-locked +dvb-frontends/rtl2830 Parent-locked +dvb-frontends/rtl2832 Mux-locked +dvb-frontends/si2168 Mux-locked +usb/cx231xx/ Parent-locked +======================= ============================================= diff --git a/Documentation/i2c/slave-interface.rst b/Documentation/i2c/slave-interface.rst index 82ea3e1d6fe4..58fb143baee4 100644 --- a/Documentation/i2c/slave-interface.rst +++ b/Documentation/i2c/slave-interface.rst @@ -32,9 +32,9 @@ User manual =========== I2C slave backends behave like standard I2C clients. So, you can instantiate -them as described in the document 'instantiating-devices'. The only difference -is that i2c slave backends have their own address space. So, you have to add -0x1000 to the address you would originally request. An example for +them as described in the document instantiating-devices.rst. The only +difference is that i2c slave backends have their own address space. So, you +have to add 0x1000 to the address you would originally request. An example for instantiating the slave-eeprom driver from userspace at the 7 bit address 0x64 on bus 1:: diff --git a/Documentation/i2c/writing-clients.rst b/Documentation/i2c/writing-clients.rst index e3b126cf4a3b..47f7cbf4ed1a 100644 --- a/Documentation/i2c/writing-clients.rst +++ b/Documentation/i2c/writing-clients.rst @@ -364,7 +364,7 @@ stop condition is issued between transaction. The i2c_msg structure contains for each message the client address, the number of bytes of the message and the message data itself. -You can read the file ``i2c-protocol`` for more information about the +You can read the file i2c-protocol.rst for more information about the actual I2C protocol. @@ -414,7 +414,7 @@ transactions return 0 on success; the 'read' transactions return the read value, except for block transactions, which return the number of values read. The block buffers need not be longer than 32 bytes. -You can read the file ``smbus-protocol`` for more information about the +You can read the file smbus-protocol.rst for more information about the actual SMBus protocol. |