diff options
Diffstat (limited to 'Documentation/i2c/slave-interface')
| -rw-r--r-- | Documentation/i2c/slave-interface | 24 |
1 files changed, 15 insertions, 9 deletions
diff --git a/Documentation/i2c/slave-interface b/Documentation/i2c/slave-interface index 61ed05cd9531..7e2a228f21bc 100644 --- a/Documentation/i2c/slave-interface +++ b/Documentation/i2c/slave-interface @@ -139,12 +139,17 @@ If you want to add slave support to the bus driver: * implement calls to register/unregister the slave and add those to the struct i2c_algorithm. When registering, you probably need to set the i2c slave address and enable slave specific interrupts. If you use runtime pm, you - should use pm_runtime_forbid() because your device usually needs to be powered - on always to be able to detect its slave address. When unregistering, do the - inverse of the above. + should use pm_runtime_get_sync() because your device usually needs to be + powered on always to be able to detect its slave address. When unregistering, + do the inverse of the above. * Catch the slave interrupts and send appropriate i2c_slave_events to the backend. +Note that most hardware supports being master _and_ slave on the same bus. So, +if you extend a bus driver, please make sure that the driver supports that as +well. In almost all cases, slave support does not need to disable the master +functionality. + Check the i2c-rcar driver as an example. @@ -173,13 +178,14 @@ During development of this API, the question of using buffers instead of just bytes came up. Such an extension might be possible, usefulness is unclear at this time of writing. Some points to keep in mind when using buffers: -* Buffers should be opt-in and slave drivers will always have to support - byte-based transactions as the ultimate fallback because this is how the - majority of HW works. +* Buffers should be opt-in and backend drivers will always have to support + byte-based transactions as the ultimate fallback anyhow because this is how + the majority of HW works. -* For backends simulating hardware registers, buffers are not helpful because - on writes an action should be immediately triggered. For reads, the data in - the buffer might get stale. +* For backends simulating hardware registers, buffers are largely not helpful + because after each byte written an action should be immediately triggered. + For reads, the data kept in the buffer might get stale if the backend just + updated a register because of internal processing. * A master can send STOP at any time. For partially transferred buffers, this means additional code to handle this exception. Such code tends to be |