On Fri, Jan 19, 2018 at 07:07:29PM +0100, Marcin Wojtas wrote:

Hi Mika,

Hi,

2018-01-18 14:00 GMT+01:00 Andrew Lunn [off-list ref]:

quoted

quoted

I CC'ed Mika since he is more familiar with handling these bits of ACPI
specs - I wonder whether this is a problem that cropped up on x86
systems too.

Hi Lorenzo

There is nothing about MDIO, PHYs, Ethernet switches, etc in version
6.2 of the spec. If x86 has this, it must be after 6.2 was released.
I would not be too surprised if x86 has none of this. If you look at
the typical drives used on x86, i210, e1000e, ixgb, r8169, etc. They
are all PCI devices, and hide all this.

quoted

I do not think there is one and only answer but there must be a single
set of bindings and if the ACPI specs already cater for some of them
we have to reuse them.

Agreed. Due diligence so far suggests there is nothing already
defined. But im a newbie to ACPI, so could be looking in the wrong
place. I really hope there is somebody like Rob Herring, the DT
maintainer, who keeps an eye on all ACPI talk and would tell us if we
are heading off in the wrong direction.

My initial approach with MDIO bus with PHYs as child nodes was super
easy to describe and handle in Linux - please refer to:
- typical representation of mdio bus with the phys -
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/devicetree/bindings/net/mdio.txt?h=v4.15-rc8
- my patches in the initial series
However I guess it would be more proper to use the
GenericSerialBus-based description, as advised in ACPI Spec. The
question is, whether we should define new type of a bus or not
(MdioSerialBus, similar to e.g. I2cSerialBus).

I'm not familiar with MDIO bus but an alternative to GeneriSerialBus
would be to follow what SDIO is doing, e.g have the PHY devices listed
below the MDIO controller and use _ADR to describe their "address" on
that bus. You can see how _ADR applies to SDIO bus from ACPI spec.

Of course ACPI spec should then be updated accordingly to describe what
_ADR means for devices on MDIO bus.

Since I have a code that can be tested and easily modified to use
different ACPI approaches with real platform MDIO controller
(mvmdio.c) and NIC (mvpp2.c), in coming weeks I may be able to find
some time to prepare a proof of concept based on GenericSerialBus.
Please expect some RFC patches hopefully right after the coming merge
window is closed.

Of course, if I come up on some ACPI - specific implementation
questions, I won't hesitate to ask in this thred. I will also
appreciate any hints. For now my two main concerns are:
- The PHY address on the mdio bus - should it be put into _CRS ->
GenericSerialBus() field or separate _ADR? I'd lean towards first
option.
- The PHY type - in Linux it's resolved basing on two generic
compatible strings
(https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/devicetree/bindings/net/phy.txt?h=v4.15-rc8).
I'd put it as a sort of ID into GenericSerialBus(). If you agree - any
specific filed that you would try to use?

If you go with the SDIO way then each PHY is described as normal ACPI
device and you can use ACPI _HID/_CID to match the device to the
corresponding driver.

Do I understand correctly that the MDIO controller node should
comprise OperationRegion() definition of the GenericSerialBus?

I don't think OpRegions are useful in this case because they are mainly
used to allow BIOS AML code to access the hardware through OS driver.