On Wednesday, September 30, 2015 12:43:36 PM Mika Westerberg wrote:
> 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.
The idea is to use _ADR kind of instead of "PRP0001" to express the "you
don't need a driver for this" idea AFAICS.
> > 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)]
Yes, it is a gray area, but I think it is reasonable.
> > 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.
Me neither.
Thanks,
Rafael
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