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Message-ID: <20151012105023.GX1506@lahna.fi.intel.com>
Date: Mon, 12 Oct 2015 13:50:23 +0300
From: Mika Westerberg <mika.westerberg@...ux.intel.com>
To: Dustin Byford <dustin@...ulusnetworks.com>
Cc: Wolfram Sang <wsa@...-dreams.de>, linux-i2c@...r.kernel.org,
linux-kernel@...r.kernel.org, rjw@...ysocki.net
Subject: Re: [PATCH 2/2] i2c: add ACPI support for I2C mux ports
On Fri, Oct 09, 2015 at 05:41:47PM -0700, Dustin Byford wrote:
> Although I2C mux devices are easily enumerated using ACPI (_HID/_CID or
> device property compatible string match) enumerating I2C client devices
> connected through a I2C mux device requires a little extra work.
>
> This change implements a method for describing an I2C device hierarchy that
> includes mux devices by using an ACPI Device() for each mux channel along
> with an _ADR to set the channel number for the device. See
> Documentation/acpi/i2c-muxes.txt for a simple example.
>
> Signed-off-by: Dustin Byford <dustin@...ulusnetworks.com>
> ---
> Documentation/acpi/i2c-muxes.txt | 58 ++++++++++++++++++++++++++++++++++++++++
> drivers/i2c/i2c-core.c | 18 +++++++++++--
> drivers/i2c/i2c-mux.c | 8 ++++++
> 3 files changed, 82 insertions(+), 2 deletions(-)
> create mode 100644 Documentation/acpi/i2c-muxes.txt
>
> diff --git a/Documentation/acpi/i2c-muxes.txt b/Documentation/acpi/i2c-muxes.txt
> new file mode 100644
> index 0000000..efdcf0d
> --- /dev/null
> +++ b/Documentation/acpi/i2c-muxes.txt
> @@ -0,0 +1,58 @@
> +ACPI I2C Muxes
> +--------------
> +
> +Describing an I2C device hierarchy that includes I2C muxes requires an ACPI
> +Device() scope per mux channel.
> +
> +Consider this topology:
> +
> ++------+ +------+
> +| SMB1 |-->| MUX0 |--CH00--> i2c client A (0x50)
> +| | | 0x70 |--CH01--> i2c client B (0x50)
> ++------+ +------+
> +
> +which corresponds to the following ASL:
> +
> +Device(SMB1)
> +{
> + Name (_HID, ...)
> + Device(MUX0)
Nit: please be consistent:
Name ()
Device ()
> + {
> + Name (_HID, ...)
> + Name (_CRS, ResourceTemplate () {
> + I2cSerialBus (0x70, ControllerInitiated, I2C_SPEED,
> + AddressingMode7Bit, "^SMB1", 0x00,
> + ResourceConsumer,,)
> + }
> +
> + Device(CH00)
> + {
> + Name (_ADR, 0)
> +
> + Device(CLIA)
> + {
> + Name (_HID, ...)
> + Name (_CRS, ResourceTemplate () {
> + I2cSerialBus (0x50, ControllerInitiated, I2C_SPEED,
> + AddressingMode7Bit, "^CH00", 0x00,
> + ResourceConsumer,,)
> + }
> + }
> + }
> +
> + Device(CH01)
> + {
> + Name (_ADR, 1)
> +
> + Device(CLIB)
> + {
> + Name (_HID, ...)
> + Name (_CRS, ResourceTemplate () {
> + I2cSerialBus (0x50, ControllerInitiated, I2C_SPEED,
> + AddressingMode7Bit, "^CH01", 0x00,
> + ResourceConsumer,,)
> + }
> + }
> + }
> + }
> +}
> diff --git a/drivers/i2c/i2c-core.c b/drivers/i2c/i2c-core.c
> index 3a4c54e..a2de010 100644
> --- a/drivers/i2c/i2c-core.c
> +++ b/drivers/i2c/i2c-core.c
> @@ -156,7 +156,10 @@ static acpi_status acpi_i2c_add_device(acpi_handle handle, u32 level,
> info.fwnode = acpi_fwnode_handle(adev);
>
> memset(&lookup, 0, sizeof(lookup));
> - lookup.adapter_handle = ACPI_HANDLE(adapter->dev.parent);
> + if (i2c_parent_is_i2c_adapter(adapter))
> + lookup.adapter_handle = ACPI_HANDLE(&adapter->dev);
> + else
> + lookup.adapter_handle = ACPI_HANDLE(adapter->dev.parent);
So I don't really like this.
Isn't there any other way to figure out the right companion for the
device?
> lookup.device_handle = handle;
> lookup.info = &info;
>
> @@ -210,9 +213,20 @@ static acpi_status acpi_i2c_add_device(acpi_handle handle, u32 level,
> */
> static void acpi_i2c_register_devices(struct i2c_adapter *adap)
> {
> + struct device *dev;
> acpi_status status;
>
> - if (!adap->dev.parent || !has_acpi_companion(adap->dev.parent))
> + /*
> + * Typically we look at the ACPI device's parent for an ACPI companion.
> + * However, in the case of an I2C-connected I2C mux, the "virtual" I2C
> + * adapter allocated for the mux channel has that association.
> + */
> + if (i2c_parent_is_i2c_adapter(adap))
> + dev = &adap->dev;
> + else
> + dev = adap->dev.parent;
Ditto.
> +
> + if (!has_acpi_companion(dev))
> return;
>
> status = acpi_walk_namespace(ACPI_TYPE_DEVICE, ACPI_ROOT_OBJECT,
> diff --git a/drivers/i2c/i2c-mux.c b/drivers/i2c/i2c-mux.c
> index 2ba7c0f..00fc5b1 100644
> --- a/drivers/i2c/i2c-mux.c
> +++ b/drivers/i2c/i2c-mux.c
> @@ -25,6 +25,7 @@
> #include <linux/i2c.h>
> #include <linux/i2c-mux.h>
> #include <linux/of.h>
> +#include <linux/acpi.h>
>
> /* multiplexer per channel data */
> struct i2c_mux_priv {
> @@ -173,6 +174,13 @@ struct i2c_adapter *i2c_add_mux_adapter(struct i2c_adapter *parent,
> }
> }
>
> + /*
> + * Associate the mux channel with an ACPI node.
> + */
> + if (has_acpi_companion(mux_dev))
> + acpi_preset_companion(&priv->adap.dev, ACPI_COMPANION(mux_dev),
> + chan_id);
> +
> if (force_nr) {
> priv->adap.nr = force_nr;
> ret = i2c_add_numbered_adapter(&priv->adap);
> --
> 2.1.4
--
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