On 13.03.2018 17:27, Felipe Balbi wrote:
Hi,
Mathias Nyman <mathias.nyman@xxxxxxxxxxxxxxx> writes:
The USB 3.2 specification adds support for Dual-lane, doubling the
maximum rate to 20Gbps by taking into use another set of rx and tx
wires and pins in the Type-C cable and connector.
The changes to support this in USB core and xhci driver seems to be minor.
USB 3.1 support already added the extended port status request returning
lane count. it just wasn't used before.
I'd like to use these patches to start a discussion about which items
regarding Dual-lane and USB 3.2 should be exposed to userspace and how.
These patches add a variable "lanes" to store the number of lanes
in use, and adds the Gen XxY notion to the string displayed when a new
device is connected. X in Gen XxY stands for signaling rate,
Y for lane count, as described in the USB 3.2 specification.
Example for clarification:
Gen 1x1 = 5Gbps, SuperSpeed, one lane, same as USB3.0, and USB 3.1 Gen1
Gen 2x1 = 10Gbps, SuperSpeedPlus, one lane, same as USB 3.1 Gen2
Gen 1x2 = 10Gbps, SuperSpeed, Dual-lane (2 x 5Gbps)
Gen 2x2 = 20Gbps, SuperSpeedPlus, Dual-lane (2 x 10Gbps)
it's a little more interesting than that, no?
IIRC, we can Gen 2x2 RX and Gen 2x1 TX (and vice-versa).
My understanding is that Gen XxY notion is only used for symmetric devices
where tx lanes = rx lanes. Only SSIC devices can be asymmetric.
USB 3.2 spec mentions the (Gen 1x1, 1x2, 2x1 and 2x2) alternatives, nothing more.
Nothing about different lane counts on rx and tx related to Gen XxY.
USB 3.2 section 8.5.6.7:
"Asymmetric Lane Types may only be reported by SuperSpeed Interchip (SSIC) devices. A
Symmetric link is one that has the same Lane Speed and number of lanes for both the Rx and
Tx Sublinks. Enhanced SuperSpeed devices shall only support Symmetric links
SSIC spec doesn't mention Gen XxY or any "Gen" at all, SSIC can support x1, x2 or x4 lanes,
but only at SuperSpeed 5Gbps signaling rate per lane.
-Mathias
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