Commit graph

5 commits

Author SHA1 Message Date
Simon Glass
4082fce924 dm: i2c: Allow muxes to be enabled for SPL separately
Since I2C muxes are seldom needed in SPL, and the code for this increases
the size somewhat, add a separate option to enable I2C muxes for SPL.

Signed-off-by: Simon Glass <sjg@chromium.org>
2016-01-21 20:42:35 -07:00
Michal Simek
0305be1087 Kconfig: i2c: Fix indentation
Use tabs instead of space for indentation.

Signed-off-by: Michal Simek <michal.simek@xilinx.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
2015-12-11 06:30:01 +01:00
Michal Simek
61d815a2cb Kconfig: i2c: Fix typo Suport -> Support
Fix typo in command description.

Signed-off-by: Michal Simek <michal.simek@xilinx.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
2015-12-11 06:29:54 +01:00
Simon Glass
b725dc458f i2c: Add a mux for GPIO-based I2C bus arbitration
While I2C supports multi-master buses this is difficult to get right.
The implementation on the master side in software is quite complex.
Clock-stretching and the arbitrary time that an I2C transaction can take
make it difficult to share the bus fairly in the face of high traffic.
When one or more masters can be reset independently part-way through a
transaction it is hard to know the state of the bus.

This driver provides a scheme based on two 'claim' GPIOs, one driven by the
AP (Application Processor, meaning the main CPU) and one driven by the EC
(Embedded Controller, a small CPU aimed at handling system tasks). With
these they can communicate and reliably share the bus. This scheme has
minimal overhead and involves very little code. It is used on snow to
permit the EC and the AP to share access to the main system PMIC and
battery. The scheme can survive reboots by either side without difficulty.
This scheme has been tested in the field with millions of devices.

Since U-Boot runs on the AP, the terminology used is 'our' claim GPIO,
meaning the AP's, and 'their' claim GPIO, meaning the EC's. This terminology
is used by the device tree bindings in Linux also.

Signed-off-by: Simon Glass <sjg@chromium.org>
2015-08-05 21:06:10 -06:00
Simon Glass
3d1957f0ea dm: i2c: Add support for multiplexed I2C buses
Add a new I2C_MUX uclass. Devices in this class can multiplex between
several I2C buses, selecting them one at a time for use by the system.
The multiplexing mechanism is left to the driver to decide - it may be
controlled by GPIOs, for example.

The uclass supports only two methods: select() and deselect().

The current mux state is expected to be stored in the mux itself since
it is the only thing that knows how to make things work. The mux can
record the current state and then avoid switching unless it is necessary.
So select() can be skipped if the mux is already in the correct state.
Also deselect() can be made a nop if required.

Signed-off-by: Simon Glass <sjg@chromium.org>
2015-08-05 21:06:10 -06:00