Re: [PATCH v12 2/4] phy: Add ethernet serdes configuration option

Hi Steen,

On 15/01/21 9:44 pm, Steen Hegelund wrote:

Hi Kishon,

On Fri, 2021-01-15 at 21:22 +0530, Kishon Vijay Abraham I wrote:

quoted

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Hi,

On 07/01/21 2:49 pm, Steen Hegelund wrote:

quoted

Provide a new ethernet phy configuration structure, that
allow PHYs used for ethernet to be configured with
speed, media type and clock information.

Signed-off-by: Lars Povlsen <redacted>
Signed-off-by: Steen Hegelund <steen.hegelund@microchip.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
---
 include/linux/phy/phy-ethernet-serdes.h | 30
+++++++++++++++++++++++++
 include/linux/phy/phy.h                 |  4 ++++
 2 files changed, 34 insertions(+)
 create mode 100644 include/linux/phy/phy-ethernet-serdes.h

diff --git a/include/linux/phy/phy-ethernet-serdes.h

b/include/linux/phy/phy-ethernet-serdes.h
new file mode 100644
index 000000000000..d2462fadf179

--- /dev/null
+++ b/include/linux/phy/phy-ethernet-serdes.h

@@ -0,0 +1,30 @@
+/* SPDX-License-Identifier: (GPL-2.0 OR MIT) */
+/*
+ * Microchip Sparx5 Ethernet SerDes driver
+ *
+ * Copyright (c) 2020 Microschip Inc
+ */
+#ifndef __PHY_ETHERNET_SERDES_H_
+#define __PHY_ETHERNET_SERDES_H_
+
+#include <linux/types.h>
+
+enum ethernet_media_type {
+     ETH_MEDIA_DEFAULT,
+     ETH_MEDIA_SR,
+     ETH_MEDIA_DAC,
+};

I'm not familiar with Ethernet. Are these generic media types? what
does
SR or DAC refer to? 

The SR stands for Short Reach and is a fiber type connection used by
SFPs.  There also other "reach" variants.

DAC stands for Direct Attach Copper and is a type of cable that plugs
into an SFP cage and provides information back to the user via its
EEPROM regarding supported speed and capabilities in general.  These
typically supports speed of 5G or more.

The SFP/Phylink is the "out-of-band" method that provides the type of
connection: speed and media type that allows the client to adapt the
SerDes configuration to the type of media selected by the user.

quoted

Are there other media types? What is the out-of-band
mechanism by which the controller gets the media type? Why was this
not
required for other existing Ethernet SERDES? 

This is probably a matter of the interface speed are now getting higher
and the amount of configuration needed for the SerDes have increased,
at the same time as this is not being a static setup, because the user
an plug and unplug media to the SFP cage.

quoted

Are you aware of any other
vendors who might require this?

I suspect that going forward it will become more widespread, at least
we have more chips in the pipeline that need this SerDes for high speed
connectivity.

For this case I would recommend to add new API, something like
phy_set_media(). Configure() and Validate() is more for probing
something that is supported by SERDES and changing the parameters. But
in this case, I'd think the media type is determined by the cable that
is connected and cannot be changed.

Thanks
Kishon