On Tue, Sep 29, 2015 at 04:19:12PM -0700, Dustin Byford wrote:
> Hi Mika,
>
> On Mon Aug 17 15:03, Mika Westerberg wrote:
> > I think the current code in I2C core is not actually doing the right
> > thing according the ACPI spec at least. To my understanding you can have
> > device with I2cSerialBus resource _anywhere_ in the namespace, not just
> > directly below the host controller. It's the ResourceSource attribute
> > that tells the corresponding host controller.
> >
> > I wonder if it helps if we scan the whole namespace for devices with
> > I2cSerialBus that matches the just registered adapter? Something like
> > the patch below.
>
> I've been working with the patch you suggested below.
>
> > diff --git a/drivers/i2c/i2c-core.c b/drivers/i2c/i2c-core.c
> > index c83e4d13cfc5..2a309d27421a 100644
> > --- a/drivers/i2c/i2c-core.c
> > +++ b/drivers/i2c/i2c-core.c
>
> ...
>
> > static void acpi_i2c_register_devices(struct i2c_adapter *adap)
> > {
> > - acpi_handle handle;
> > acpi_status status;
> >
> > - if (!adap->dev.parent)
> > - return;
> > -
> > - handle = ACPI_HANDLE(adap->dev.parent);
> > - if (!handle)
> > + if (!adap->dev.parent || !has_acpi_companion(adap->dev.parent))
> > return;
> >
> > - status = acpi_walk_namespace(ACPI_TYPE_DEVICE, handle, 1,
> > + status = acpi_walk_namespace(ACPI_TYPE_DEVICE, ACPI_ROOT_OBJECT,
> > + ACPI_I2C_MAX_SCAN_DEPTH,
> > acpi_i2c_add_device, NULL,
> > adap, NULL);
>
> On my systems (which admittedly all define their i2c clients below the
> controller) this works as expected, i.e. there's no change in behavior.
> As far as I can tell it more accurately implements the spec.
>
>
> However, it doesn't quite solve my problem. When
> acpi_i2c_register_devices(adap) is called on the "virtual" controller
> that is created for an i2c mux channel, the adap->dev.parent (set to the
> parent i2c bus for the mux) does not have an acpi companion. That
> ultimately causes acpi_i2c_add_device() to never find a match.
>
> I'll recap a bit since it's been a while and I've learned a few things
> that might affect the discussion. For now, I'll focus on my proposed
> ASL for an I2C mux using device properties.
>
> Lets say we have i2c hardware attached like this:
>
> i801 controller (PCI)
> pca9548 8-channel mux (address 0x70)
> lm75 temperature sensor (channel 0 on the mux with address 0x50)
>
> I think this is a sensible way to represent it:
>
> Device (MUX0) {
> Name (_ADR, 0x70)
This..
> Name (_HID, "PRP0001")
> Name (_CRS, ResourceTemplate()
> {
> I2cSerialBus (0x70, ControllerInitiated, I2C_SPEED,
> AddressingMode7Bit, "^^SMB2", 0x00,
> ResourceConsumer,,)
> })
> Name (_DSD, Package ()
> {
> ToUUID("daffd814-6eba-4d8c-8a91-bc9bbf4aa301"),
> Package () {
> Package (2) { "compatible", "nxp,pca9548" },
> }
> })
>
> // MUX channel 0
> Device (CH00) {
> Name (_ADR, 0x0)
>
> Device (TMP0) {
> Name (_ADR, 0x50)
... and this are not needed. I2cSerialBus already contains the address.
Also I think you need to have "PRP0001" here as well.
> Name (_CRS, ResourceTemplate()
> {
> I2cSerialBus (0x60, ControllerInitiated, I2C_SPEED,
> AddressingMode7Bit, "^CH00", 0x00,
> ResourceConsumer,,)
> })
> Name (_DSD, Package ()
> {
> ToUUID("daffd814-6eba-4d8c-8a91-bc9bbf4aa301"),
> Package () {
> Package (2) { "compatible", "national,lm75" },
> }
> })
> }
> }
> }
>
> The new thing here is using _ADR to treat each mux channel as a device
> and referencing those devices elsewhere (CH00). I arrived at this
> because it seems to fit the ACPI model reasonably well* and it's easy to
> implement (just like in other callers to acpi_preset_companion())
>
> * by reasonably well, I think it's clear and works naturally but this
> use of _ADR isn't explicitly defined in the spec [ACPI 6, Table 6-168
> (page 278)]
>
> Hopefully the spec ambiguity isn't too much effort to clarify. I think
> it's a good change. But, perhaps it's unnecessary. Any feedback on
> whether this ASL seem like the right way to go for device property i2c
> muxes?
Well to me your ASL looks reasonable. Usage of _ADR to specify mux
channel seems natural and follows other buses which have an entry in
that table. I don't know if it is forbidden to invent this kind of
things that are not explicitly mentioned in the spec, though.
> If not, is there an acceptable alternative? I wonder how muxes are
> handled otherwise? Hopefully not ASL methods :)
I cannot think of any better way. I have never seen ACPI DSDT/SSDT
containing I2C mux before.
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