[RFC PATCH 0/1] i2c: scan ACPI enumerated I2C mux channels

From: Dustin Byford
Date: Thu Aug 13 2015 - 19:59:29 EST

I would like to add support for scanning I2C devices connected to ACPI
OF compatible muxes described in ASL like this:

Device (MUX0)
Name (_ADR, 0x70)
Name (_HID, "PRP0001")
Name (_CRS, ResourceTemplate()
I2cSerialBus (0x70, ControllerInitiated, I2C_SPEED,
AddressingMode7Bit, "^^SMB2", 0x00,
Name (_DSD, Package ()
Package () {
Package (2) { "compatible", "nxp,pca9548" },

// MUX channels
Device (CH00) { Name (_ADR, 0x0) }

Device (TMP0) {
/* Temp sensor ASL, for example. */

It seems like a reasonable way to describe a common I2C component and
kernel support is almost there.

I had to:

1) Find and set an ACPI companion for the "virtual" I2C adapters created
for each mux channel.

2) Make sure to scan adap.dev when registering devices under each mux

At first, I was confused about why adap.dev->parent is used in
acpi_i2c_register_devices(). I found b34bb1ee from 4/2013 (ACPI / I2C:
Use parent's ACPI_HANDLE()), which offers an explanation.

This patch works well, but I'm not sure about the code to just fall back
to using adap.dev when adap.dev->parent doesn't have an ACPI companion.
Is there a more explicit check I can make to determine if the adapter
represents a mux channel?

Any feedback would be welcome. Thanks,


Dustin Byford (1):
i2c: acpi: scan ACPI enumerated I2C mux channels

drivers/i2c/i2c-core.c | 10 ++++++++++
drivers/i2c/i2c-mux.c | 8 ++++++++
2 files changed, 18 insertions(+)


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