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Diffstat (limited to 'Documentation/devicetree/bindings/i2c/i2c-arb-gpio-challenge.txt')
-rw-r--r-- | Documentation/devicetree/bindings/i2c/i2c-arb-gpio-challenge.txt | 82 |
1 files changed, 0 insertions, 82 deletions
diff --git a/Documentation/devicetree/bindings/i2c/i2c-arb-gpio-challenge.txt b/Documentation/devicetree/bindings/i2c/i2c-arb-gpio-challenge.txt deleted file mode 100644 index 548a73cde796..000000000000 --- a/Documentation/devicetree/bindings/i2c/i2c-arb-gpio-challenge.txt +++ /dev/null @@ -1,82 +0,0 @@ -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. - -Note that this scheme works well enough but has some downsides: -* It is nonstandard (not using standard I2C multimaster) -* Having two masters on a bus in general makes it relatively hard to debug - problems (hard to tell if i2c issues were caused by one master, another, or - some device on the bus). - - -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. -- I2C arbitration bus node. See i2c-arb.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"; - - 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-arb { - #address-cells = <1>; - #size-cells = <0>; - - i2c@52 { - // Normal I2C device - }; - }; - }; |