On Tue, 22 Apr 2014, Doug Anderson wrote: > On ARM Chromebooks we have a few devices that are accessed by both the > AP (the main "Application Processor") and the EC (the Embedded > Controller). These are: > * The battery (sbs-battery). > * The power management unit tps65090. > > On the original Samsung ARM Chromebook these devices were on an I2C > bus that was shared between the AP and the EC and arbitrated using > some extranal GPIOs (see i2c-arb-gpio-challenge). > > The original arbitration scheme worked well enough but had some > downsides: > * It was nonstandard (not using standard I2C multimaster) > * It only worked if the EC-AP communication was I2C > * It was relatively hard to debug problems (hard to tell if i2c issues > were caused by the EC, the AP, or some device on the bus). > > On the HP Chromebook 11 the design was changed to: > * The AP/EC comms were still i2c, but the battery/tps65090 were no > longer on the bus used for AP/EC communication. The battery was > exposed to the AP through a limited i2c tunnel and tps65090 was > exposed to the AP through a custom Linux driver. > > On the Samsung ARM Chromebook 2 the scheme is changed yet again, now: > * The AP/EC comms are now using SPI for faster speeds. > * The EC's i2c bus is exposed to the AP through a full i2c tunnel. > > The upstream "tegra124-venice2" uses the same scheme as the Samsung > ARM Chromebook 2, though it has a different set of components on the > other side of the bus. > > This driver supports the scheme used by the Samsung ARM Chromebook 2. > Future patches to this driver could add support for the battery tunnel > on the HP Chromebook 11 (and perhaps could even be used to access > tps65090 on the HP Chromebook 11 instead of using a special driver, > but I haven't researched that enough). > > Signed-off-by: Vincent Palatin <vpalatin@xxxxxxxxxxxx> > Signed-off-by: Simon Glass <sjg@xxxxxxxxxxxx> > Signed-off-by: Doug Anderson <dianders@xxxxxxxxxxxx> > Tested-by: Andrew Bresticker <abrestic@xxxxxxxxxxxx> > Tested-by: Stephen Warren <swarren@xxxxxxxxxx> > --- > Changes in v2: > - Update tunnel binding as per swarren > > .../devicetree/bindings/i2c/i2c-cros-ec-tunnel.txt | 39 +++ > drivers/i2c/busses/Kconfig | 9 + > drivers/i2c/busses/Makefile | 1 + > drivers/i2c/busses/i2c-cros-ec-tunnel.c | 304 +++++++++++++++++++++ > drivers/mfd/cros_ec.c | 5 + For the MFD changes: Acked-by: Lee Jones <lee.jones@xxxxxxxxxx> -- Lee Jones Linaro STMicroelectronics Landing Team Lead Linaro.org │ Open source software for ARM SoCs Follow Linaro: Facebook | Twitter | Blog -- To unsubscribe from this list: send the line "unsubscribe linux-i2c" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
