HW:APCIe - AsahiLinux/docs GitHub Wiki
The PCIe host bridge includes at least some Synopsys DesignWare derived logic. The release version encoded at offset 0x8f8/0x8fc in PCIE config space indicates version 530*-ea15 (5.30a-ea15).
| Property | Value | Meaning |
|---|---|---|
| compatible | apcie,t8103 | compatible string |
| #address-cells | 3 | normal PCI DT: <BAR type><addr>len>
|
| #size-cells | 2 | normal PCI DT |
| interrupt-parent | - | phandle of AIC |
| interrupts | (0x2b7, 0x2ba, 0x2bd) | Administrative interrupts. Maybe AER? |
| msi-parent-controller | - | phandle of AIC |
| #msi-vectors | 32 | number of IRQs in AIC for MSI |
| msi-address | 0xfffff000 | program this into the MSI-X address BAR |
| msi-vector-offset | 0x2c0 | (this + msi_id) go to the MSI-X value field in the MSI-X device BAR |
| #ports | 3 | number of DART bindings |
| apcie-common-tunables | 0x2c, 0x4, 0xff, 0x0, 0x1, 0x0, 0x54, 0x4, 0xffffffff, 0x0, 0x140, 0x0 | ? |
| apcie-axi2af-tunables | todo | ? |
| apcie-phy-tunables | todo | ? |
| apcie-phy-ip-pll-tunables | todo | ? |
| apcie-phy-ip-auspma-tunables | todo | ? |
| Address | Length | Meaning |
|---|---|---|
| 0x690000000 | 0x10000000 | ECAM space |
| 0x680000000 | 0x40000 | Ctrl |
| 0x680080000 | 0x90000 | Phy config |
| 0x6800c0000 | 0x20000 | ? |
| 0x68c000000 | 0x4000 | ? |
| 0x3d2bc000 | 0x1000 | ? |
| 0x681000000 | 0x8000 | port0 link / control registers |
| 0x681010000 | 0x1000 | port0 |
| 0x680084000 | 0x4000 | port0 phy |
| 0x6800c8000 | 0x16610 | port0 |
| 0x682000000 | 0x8000 | port1 link / control registers |
| 0x682010000 | 0x1000 | port1 |
| 0x680088000 | 0x4000 | port1 phy |
| 0x6800d0000 | 0x6000 | port1 |
| 0x683000000 | 0x8000 | port2 link / control registers |
| 0x683010000 | 0x1000 | port2 |
| 0x68008c000 | 0x4000 | port2 phy |
| 0x6800d8000 | 0x6000 | port2 |
| Space | Offset | name | Meaning / Values |
|---|---|---|---|
| Ctrl | 0x28 | Refclk | 1 << 4 is good |
| Ctrl | 0x50 | ? | Write 1 to enable PCIe |
| Ctrl | 0x58 | ? | Reads 1 after 0x50 write |
| Phy config | 0x0 | ? | Writing bits 0x1 and 0x2 toggle 0x4 and 0x8 respectively |
| portX link | 0x100 | pcielint | |
| portX link | 0x208 | linksts | Bit 0x1 means link is enabled. Requires write to 0x804 |
| portX link | 0x210 | linkcdmsts | |
| portX link | 0x800 | ? | Read in initializeRootComplex() |
| portX link | 0x804 | ? | Read in enablePortHardware() |
| portX phy | 0x0 | PhyGlueLaneReg / RefClockBuffer | Writing bits 0x1 and 0x2 toggle bits 0x4 and 0x2 respectively |
The following set of tunables operate on config space of the per-port PCIe bridge devices.
On the 2020 M1 mini, this set of register writes modifies some bits on standardized capability structures as well as some other registers.
| register | capability | effect |
|---|---|---|
| 0x194 | L1 PM Substates | clear Port Common_Mode_Restore_Time |
| clear Port T_POWER_ON Scale | ||
| clear Port T_POWER_ON Value | ||
| 0x2a4 | Data Link Feature | clear Data Link Feature Exchange Enable |
| 0xb80 | not part of an (extended) capability structure | |
| 0xb84 | not part of an (extended) capability structure | |
| 0x78 | PCI Express | clear Max_Read_Request_Size |
| register | capability | effect |
|---|---|---|
| 0x154 | Secondary PCI Express | set Downstream Port 8.0 GT/s Transmitter Preset |
| set Upstream Port 8.0 GT/s Transmitter Preset | ||
| 0x890 | not part of an (extended) capability structure | |
| appears to be the Synopsys Designware PCIe GEN3_RELATED register | ||
| 0x8a8 | not part of an (extended) capability structure | |
| appears to be the Synopsys Designware PCIe GEN3_EQ_CONTROL register |
| register | capability | effect |
|---|---|---|
| 0x178 | Physical Layer 16.0 GT/s | set Downstream Port 16.0 GT/s Transmitter Preset |
| set Upstream Port 16.0 GT/s Transmitter Preset | ||
| 0x890 | not part of an (extended) capability structure | |
| (see above) | ||
| 0x8a8 | not part of an (extended) capability structure | |
| (see above) |
So the changes to documented registers seem to disable some (buggy?) features as well do some lane equalization tuning. Maybe Apple hopes to re-enable this in a future respin of the silicon without having to specify specific silicon revs in their xnu driver?
Device tree bindings have been accepted upstream.
Some open questions remain:
- How do we enable the WiFi/BT PCIe device? This device needs to be explicitly enabled through the SMC before it shows up as a PCIe device. It has been suggested that this is how Apple implements "Airplane Mode" and there is a separate "amfm" node in the ADT for this. So maybe it makes sense to have some sort of rfkill device/node that takes care of this. Hopefully this means the APCIe device gets an interrupt when it is turned on such that we can (re)train the PCIe link.
This proposed binding has been successfully implemented/tested in u-boot and OpenBSD. However, we still need clock, pinctrl/gpio and DART bindings to make this all work.