On Tuesday, October 20, 2015 03:51:11 PM Mika Westerberg wrote:
> On Mon, Oct 19, 2015 at 03:29:00PM -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@xxxxxxxxxxxxxxxxxxx>
>
> In general this looks good to me.
>
> > ---
> > Documentation/acpi/i2c-muxes.txt | 58 ++++++++++++++++++++++++++++++++++++++++
> > drivers/i2c/i2c-core.c | 15 +++++++++--
> > drivers/i2c/i2c-mux.c | 8 ++++++
> > include/linux/acpi.h | 6 +++++
> > 4 files changed, 85 insertions(+), 2 deletions(-)
> > create mode 100644 Documentation/acpi/i2c-muxes.txt
> >
>
> [...]
>
> > + /*
> > + * By default, associate I2C adapters with their parent device's ACPI
> > + * node.
> > + */
> > + if (!has_acpi_companion(dev)) {
> > + struct acpi_device *adev = ACPI_COMPANION(dev->parent);
> > +
> > + if (adev)
> > + ACPI_COMPANION_SET(dev, adev);
>
> Instead of always doing this in the I2C core, maybe we can make it
> dependent on the host controller driver. For example the I2C designware
> driver already did this for both DT and ACPI:
>
> adap->dev.parent = &pdev->dev;
> adap->dev.of_node = pdev->dev.of_node;
> ACPI_COMPANION_SET(&adap->dev, ACPI_COMPANION(&pdev->dev));
>
> Also I would like to ask what Rafael thinks about this since he authored
> b34bb1ee71158d5b ("ACPI / I2C: Use parent's ACPI_HANDLE() in
> acpi_i2c_register_devices()").
>
> I don't see a problem multiple Linux devices sharing a single ACPI
> companion device like in this patch but I may be forgetting something ;-)
Well, we already have that in the MFD case, but in principle it may be
problematic for things like power management (say you want to put a
child device into D3, so you use _PS3 on its ACPI companion and then
the parent is powere down instead).
At least, devices in that setup should not be attached to the ACPI PM
domain.
Thanks,
Rafael
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