Re: [PATCH net-next 06/19] net: usb: aqc111: Introduce link management

Hi Andrew,

quoted

 	aqc111_read_fw_version(dev, aqc111_data);
+	aqc111_data->autoneg = AUTONEG_ENABLE;
+	aqc111_data->advertised_speed = (usb_speed == USB_SPEED_SUPER) ?
+					 SPEED_5000 : SPEED_1000;

USB 3 has a raw bandwidth of 5Gbps. But it is a shared bus. So you
have no guaranteed you are actually going to get the needed bandwidth
to support line rate.

USB 2.0 only gives you 480Mbps. So it won't even give you the full
1G. So using the same reasoning for USB3, maybe you should limit it to
100Mbps?

I personally would not apply restrictions on the PHY depending on what
USB is being used.

First argument here is to reduce power consumption on USB2.
2.5G/5G uses OCSGMII/XFI serdes which consumes more power.
Of course in normal conditions usb2 is capable to feed that, but
the risk still exists on legacy usb2 hardware.

This becomes more important when using SFPs. If i have an SFP peer
which is expecting 2500Base-X, but because the device is plugged into
USB 2 port it is forced to use 1000Base-X, it is not going to get
link.

Do you mean here 2500Base-T? This particular device is an integrated
mac+phy, thus we can't easily link it with -X SFP endpoint.

Although its not a common usecase for the consumer dongle to connect to SFP
endpoints, think your comment is quite reasonable.
We'll clarify this internally.


Regards,
  Igor