Re: [PATCH] i2c-designware: Intel BayTrail PMIC I2C bus support

[Mika Westerberg <mika.westerberg@linux.intel.com>]

On Fri, Sep 12, 2014 at 10:36:07AM -0700, David E. Box wrote:
> This patch implements an I2C bus sharing mechanism between the host and platform
> hardware on select Intel BayTrail SoC platforms using the XPower AXP288 PMIC.
> 
> On these platforms access to the PMIC must be shared with platform hardware. The
> hardware unit assumes full control of the I2C bus and the host must request
> access through a special semaphore. Hardware control of the bus also makes it
> necessary to disable runtime pm to avoid interfering with hardware transactions.

Is this because we need to access the PMIC from host as well? I mean
from some PMIC driver (which driver btw)?

Otherwise it would be best to just detect _SEM and return -ENODEV.

> 
> Signed-off-by: David E. Box <david.e.box@linux.intel.com>
> ---
>  drivers/i2c/busses/Kconfig                  |  10 +++
>  drivers/i2c/busses/Makefile                 |   1 +
>  drivers/i2c/busses/i2c-designware-core.h    |  14 ++++
>  drivers/i2c/busses/i2c-designware-platdrv.c |  78 +++++++++++++++++++--
>  drivers/i2c/busses/i2c-shared-controller.c  | 101 ++++++++++++++++++++++++++++
>  5 files changed, 200 insertions(+), 4 deletions(-)
>  create mode 100644 drivers/i2c/busses/i2c-shared-controller.c
> 
> diff --git a/drivers/i2c/busses/Kconfig b/drivers/i2c/busses/Kconfig
> index 2ac87fa..672ef23 100644
> --- a/drivers/i2c/busses/Kconfig
> +++ b/drivers/i2c/busses/Kconfig
> @@ -441,6 +441,16 @@ config I2C_DESIGNWARE_PCI
>  	  This driver can also be built as a module.  If so, the module
>  	  will be called i2c-designware-pci.
>  
> +config I2C_SHARED_CONTROLLER
> +	tristate "Intel Baytrail PMIC shared I2C bus support"
> +	depends on ACPI
> +	select IOSF_MBI
> +	select I2C_DESIGNWARE_CORE
> +	help
> +	  This driver enables shared access to the PMIC I2C bus on select Intel
> +	  BayTrail platforms using the XPower AXP288 PMIC. This driver is
> +	  required for host access to the PMIC on these platforms.

Can't we detect this runtime in the i2c-designware-platdrv.c code so
that you look (in the ACPI part of the driver) for _SEM and in that case
change the xfer function behaviour a bit to return -EBUSY or whatever?

Without this horrible #ifdeffery.