On Tuesday, October 20, 2015 10:49:59 AM Dustin Byford wrote:
> Hi Mika,
>
> On Tue Oct 20 15:51, 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:
>
> I considered it, but I thought a default that fairly closely matches the
> old behavior was more convenient.
>
> On the other hand, leaving it up to the controllers makes it all very
> explicit and perhaps simpler to reason about.
>
>
> I could be convinced either way. But, if we move it to the controller
> drivers, which ones need the change?
>
> grep -i acpi drivers/i2c/busses/i2c*
>
> shows 18 drivers that might care.
>
> > adap->dev.parent = &pdev->dev;
> > adap->dev.of_node = pdev->dev.of_node;
> > ACPI_COMPANION_SET(&adap->dev, ACPI_COMPANION(&pdev->dev));
>
> Interesting, this code isn't in my tree. I wonder why it was added,
> what code looks at the acpi companion on the i2c dev? Before my change
> it was supposed to be NULL, and it is NULL on every other controller.
As I said, IMO it should be NULL for i2c devices (power management is the
main reason here).
Thanks,
Rafael
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