This RFC adds an interface for Ethernet PCS (Physical Coding
Sublayer) devices and a driver for the Synopsys DesignWare Ethernet
PCS (DW XPCS) that implements it. I would like feedback on the
interface and on how the driver is structured before I post the MAC
driver that uses it.
Background
----------
On SoCs with a DW XPCS between the MAC and the SerDes, the MAC driver
has to configure the PCS and read back its link and auto-negotiation
state to bring up 1000BASE-KX, 10GBASE-R and 10GBASE-KR links in
U-Boot, for example for network boot.
U-Boot has no reusable driver for this IP.
What is in the series
---------------------
1/2 net: pcs: Add generic PCS interface
2/2 net: pcs: Add Synopsys DesignWare XPCS driver
Patch 1 adds include/pcs.h. Patch 2 adds the driver in
drivers/net/pcs/ with its Kconfig and Makefile, and hooks them into
drivers/net.
Architecture
------------
+--------------------+
| MAC driver | (follow-up patch, not in this series)
+---------+----------+
| pcs_set_config() pcs_get_state() pcs_disable()
v
+--------------------+
| include/pcs.h | patch 1: struct pcs_ops, pcs_config,
| | pcs_state
+---------+----------+
| ops of the PCS device
v
+--------------------+
| pcs-xpcs.c | patch 2: UCLASS_MISC, "snps,dw-xpcs"
| indirect window: | page register + register offset
+---------+----------+
| MMIO reg-names = "indirect", reg-io-width = <4>
v
+--------------------+ +--------------+
| DW XPCS |<----->| PMA / SerDes |<--> link partner
+--------------------+ +--------------+
1000BASE-KX: C37 AN 10GBASE-R: no AN 10GBASE-KR: C73 AN
Interface (patch 1)
-------------------
include/pcs.h defines struct pcs_ops with three operations, and an
inline wrapper for each one. A wrapper returns -ENOSYS if the driver
does not provide the operation.
pcs_set_config() select the interface mode, the auto-negotiation
type (none, Clause 37 or Clause 73) and the
speed, using struct pcs_config
pcs_get_state() report link, auto-negotiation complete and speed,
using struct pcs_state
pcs_disable() stop auto-negotiation and power the PCS down
Semantics:
- set_config() can be called again later, including after
pcs_disable(). If it fails, the PCS is left unconfigured.
- get_state() reports the speed as soon as the PCS is configured,
not when the link comes up. A powered down or unconfigured PCS
reports link, an_complete and speed as 0.
- A negative return from get_state() is an error, for example a
failed Clause 73 negotiation.
- Calling pcs_disable() again has no effect.
Driver (patch 2)
----------------
drivers/net/pcs/pcs-xpcs.c is a driver model driver for the
"snps,dw-xpcs" compatible. It is a UCLASS_MISC device and is enabled
with PCS_XPCS, which depends on MISC.
The XPCS registers are Clause 45 registers in the PMA/PMD, PCS, AN and
vendor MMDs. They are reached through the memory mapped indirect
window: the driver writes the page number of the register to the page
register of the window, then accesses the register at its offset in
the page. The selected page is cached to avoid redundant writes.
At probe the driver waits for the PCS to come out of reset and checks
the Clause 45 device ID. It does not configure a mode. The MAC driver
does that with pcs_set_config(). The driver checks the whole request
before it touches the hardware, so a bad request does not leave the
PCS half configured. It then stops auto-negotiation, programs the
mode, power cycles the PCS to latch it, and starts auto-negotiation if
the mode uses it.
Supported modes:
1000BASE-KX Clause 37 auto-negotiation
10GBASE-R fixed speed, no auto-negotiation
10GBASE-KR Clause 73 auto-negotiation
pcs_set_config() accepts only these combinations. Anything else is
rejected before the hardware is touched, with -EOPNOTSUPP for a wrong
auto-negotiation type and -EINVAL for a wrong speed or interface.
iface an_mode speed_mbps
1000BASE-KX PCS_AN_C37 0 or 1000
10GBASE-R PCS_AN_FORCED 10000 (required)
10GBASE-KR PCS_AN_C73 0 or 10000
Auto-negotiation completion is polled from pcs_get_state(). The link
status bit is latched low, so it is read twice and the second value is
reported. For Clause 73, pcs_get_state() returns an error if the link
partner cannot do 10GBASE-KR or uses Next Pages.
Devicetree
----------
The driver uses the existing "snps,dw-xpcs" binding from dts/upstream
(Bindings/net/pcs/snps,dw-xpcs.yaml), so no binding change is needed.
Only part of the binding is implemented. reg-names must be "indirect",
the window must be at least 1 KiB, and reg-io-width must be <4>. The
binding default of 2 is rejected, so the property cannot be left out.
The clocks and the interrupt are not used. The driver does not enable
clocks, so they must already be running when it probes. The gen*-PMA
compatibles are not matched.
Example node:
pcs@1f05d000 {
compatible = "snps,dw-xpcs";
reg = <0x1f05d000 0x1000>;
reg-names = "indirect";
reg-io-width = <4>;
};
Origin of the code
------------------
Some parts of the driver are influenced by the Linux XPCS driver
(drivers/net/pcs/pcs-xpcs*.c).
Design choices
--------------
UCLASS_MISC: a PCS is a UCLASS_MISC device and the MAC driver is
expected to get it by phandle. This is what the Airoha PCS driver and
airoha_eth do today. A dedicated UCLASS_PCS would be cleaner, but I
left it out of this series on purpose to keep the scope small.
No in-tree user yet: the MAC driver that calls this interface will
follow as a separate patch in about a month. Until then PCS_XPCS is
not selected by anything and not enabled in any defconfig. This is
why this is an RFC.
Questions for reviewers
-----------------------
1. Is UCLASS_MISC with the ops in include/pcs.h acceptable as a
starting point?
2. Are struct pcs_config and struct pcs_state enough for other PCS
drivers, or is something missing?
3. Auto-negotiation completion is polled from get_state() and the
interrupt is not used. Is that fine for U-Boot?
Testing
-------
Not tested on hardware yet.
Build tested with CONFIG_PCS_XPCS=y on qemu_arm64.
checkpatch.pl --strict reports no errors.
Not done
--------
- Interface modes other than the three above. More modes are planned
once this is approved.
- Clause 73 Next Pages: a link partner that uses them is rejected
- Register access over MDIO and the "direct" mapping
- Clocks and the interrupt from the binding
- PMA/SerDes initialisation: not done by this driver, it must be set
up before pcs_set_config() is called
- SPDX tags and a MAINTAINERS entry (checkpatch warnings)
- Sandbox emulation and a dm test
- A dedicated UCLASS_PCS
Akash Nair (2):
net: pcs: Add generic PCS interface
net: pcs: Add Synopsys DesignWare XPCS driver
drivers/net/Kconfig | 1 +
drivers/net/Makefile | 1 +
drivers/net/pcs/Kconfig | 12 +
drivers/net/pcs/Makefile | 1 +
drivers/net/pcs/pcs-xpcs.c | 881 +++++++++++++++++++++++++++++++++++++
include/pcs.h | 140 ++++++
6 files changed, 1036 insertions(+)
create mode 100644 drivers/net/pcs/Kconfig
create mode 100644 drivers/net/pcs/Makefile
create mode 100644 drivers/net/pcs/pcs-xpcs.c
create mode 100644 include/pcs.h
--
2.43.0
