diff options
author | Linus Torvalds <torvalds@linux-foundation.org> | 2013-05-02 14:38:53 -0700 |
---|---|---|
committer | Linus Torvalds <torvalds@linux-foundation.org> | 2013-05-02 14:38:53 -0700 |
commit | 99bece775f988a4ee21ad3db9fd413caf1704ff6 (patch) | |
tree | 5975cdcd92301e54dfe1424ec5d008898b5c9331 /Documentation | |
parent | 736a2dd2571ac56b11ed95a7814d838d5311be04 (diff) | |
parent | c39e8e4354ce4daf23336de5daa28a3b01f00aa6 (diff) |
Merge branch 'i2c/for-next' of git://git.kernel.org/pub/scm/linux/kernel/git/wsa/linux
Pull i2c changes from Wolfram Sang:
- an arbitration driver. While the driver is quite simple, it caused
discussion if we need additional arbitration on top of the one
specified in the I2C standard. Conclusion is that I accept a few
generic mechanisms, but not very specific ones.
- the core lost the detach_adapter() call. It has no users anymore and
was in the way for other cleanups. attach_adapter() is sadly still
there since there are users waiting to be converted.
- the core gained a bus recovery infrastructure. I2C defines a way to
recover if the data line is stalled. This mechanism is now in the
core and drivers can now pass some data to make use of it.
- bigger driver cleanups for designware, s3c2410
- removing superfluous refcounting from drivers
- removing Ben Dooks as second maintainer due to inactivity. Thanks
for all your work so far, Ben!
- bugfixes, feature additions, devicetree fixups, simplifications...
* 'i2c/for-next' of git://git.kernel.org/pub/scm/linux/kernel/git/wsa/linux: (38 commits)
i2c: xiic: must always write 16-bit words to TX_FIFO
i2c: octeon: use HZ in timeout value
i2c: octeon: Fix i2c fail problem when a process is terminated by a signal
i2c: designware-pci: drop superfluous {get|put}_device
i2c: designware-plat: drop superfluous {get|put}_device
i2c: davinci: drop superfluous {get|put}_device
MAINTAINERS: Ben Dooks is inactive regarding I2C
i2c: mux: Add i2c-arb-gpio-challenge 'mux' driver
i2c: at91: convert to dma_request_slave_channel_compat()
i2c: mxs: do error checking and handling in PIO mode
i2c: mxs: remove races in PIO code
i2c-designware: switch to use runtime PM autosuspend
i2c-designware: use usleep_range() in the busy-loop
i2c-designware: enable/disable the controller properly
i2c-designware: use dynamic adapter numbering on Lynxpoint
i2c-designware-pci: use managed functions pcim_* and devm_*
i2c-designware-pci: use dev_err() instead of printk()
i2c-designware: move to managed functions (devm_*)
i2c: remove CONFIG_HOTPLUG ifdefs
i2c: s3c2410: Add SMBus emulation for block read
...
Diffstat (limited to 'Documentation')
-rw-r--r-- | Documentation/devicetree/bindings/i2c/i2c-arb-gpio-challenge.txt | 80 |
1 files changed, 80 insertions, 0 deletions
diff --git a/Documentation/devicetree/bindings/i2c/i2c-arb-gpio-challenge.txt b/Documentation/devicetree/bindings/i2c/i2c-arb-gpio-challenge.txt new file mode 100644 index 000000000000..1ac8ea8ade1d --- /dev/null +++ b/Documentation/devicetree/bindings/i2c/i2c-arb-gpio-challenge.txt @@ -0,0 +1,80 @@ +GPIO-based I2C Arbitration Using a Challenge & Response Mechanism +================================================================= +This uses GPIO lines and a challenge & response mechanism to arbitrate who is +the master of an I2C bus in a multimaster situation. + +In many cases using GPIOs to arbitrate is not needed and a design can use +the standard I2C multi-master rules. Using GPIOs is generally useful in +the case where there is a device on the bus that has errata and/or bugs +that makes standard multimaster mode not feasible. + + +Algorithm: + +All masters on the bus have a 'bus claim' line which is an output that the +others can see. These are all active low with pull-ups enabled. We'll +describe these lines as: + +- OUR_CLAIM: output from us signaling to other hosts that we want the bus +- THEIR_CLAIMS: output from others signaling that they want the bus + +The basic algorithm is to assert your line when you want the bus, then make +sure that the other side doesn't want it also. A detailed explanation is best +done with an example. + +Let's say we want to claim the bus. We: +1. Assert OUR_CLAIM. +2. Waits a little bit for the other sides to notice (slew time, say 10 + microseconds). +3. Check THEIR_CLAIMS. If none are asserted then the we have the bus and we are + done. +4. Otherwise, wait for a few milliseconds and see if THEIR_CLAIMS are released. +5. If not, back off, release the claim and wait for a few more milliseconds. +6. Go back to 1 (until retry time has expired). + + +Required properties: +- compatible: i2c-arb-gpio-challenge +- our-claim-gpio: The GPIO that we use to claim the bus. +- their-claim-gpios: The GPIOs that the other sides use to claim the bus. + Note that some implementations may only support a single other master. +- Standard I2C mux properties. See mux.txt in this directory. +- Single I2C child bus node at reg 0. See mux.txt in this directory. + +Optional properties: +- slew-delay-us: microseconds to wait for a GPIO to go high. Default is 10 us. +- wait-retry-us: we'll attempt another claim after this many microseconds. + Default is 3000 us. +- wait-free-us: we'll give up after this many microseconds. Default is 50000 us. + + +Example: + i2c@12CA0000 { + compatible = "acme,some-i2c-device"; + #address-cells = <1>; + #size-cells = <0>; + }; + + i2c-arbitrator { + compatible = "i2c-arb-gpio-challenge"; + #address-cells = <1>; + #size-cells = <0>; + + i2c-parent = <&{/i2c@12CA0000}>; + + our-claim-gpio = <&gpf0 3 1>; + their-claim-gpios = <&gpe0 4 1>; + slew-delay-us = <10>; + wait-retry-us = <3000>; + wait-free-us = <50000>; + + i2c@0 { + reg = <0>; + #address-cells = <1>; + #size-cells = <0>; + + i2c@52 { + // Normal I2C device + }; + }; + }; |