Re: [PATCH v4] thunderbolt: Disable Gen 4 Recovery on Asymmetric Transitions

Mohammad Rahimi
2025-02-03T12:25:26Z

Hello.

On Mon, Feb 03, 2025 at 10:42:24AM GMT, Mika Westerberg wrote:
> Hi,
>
> On Fri, Jan 31, 2025 at 01:41:27AM +0000, Mohammad Rahimi wrote:
> > Updates the Connection Manager to disable the Gen 4 Link Recovery
> > flow before transitioning from a Symmetric Link to an Asymmetric
> > Link, as specified in recent changes to the USB4 v2 specification.
> >
> > According to the "USB4 2.0 ENGINEERING CHANGE NOTICE FORM"
> > published in September 2024, the rationale for this change is:
> >
> > "Since the default value of the Target Asymmetric Link might be
> > different than Symmetric Link and Gen 4 Link Recovery flow checks
> > this field to make sure it matched the actual Negotiated Link Width,
> > we’re removing the condition for a Disconnect in the Gen 4 Link
> > Recovery flow when Target Asymmetric Link doesn’t match the actual
> > Link width and adding a Connection Manager note to Disable Gen 4 Link
> > Recovery flow before doing Asymmetric Transitions."
> >
> > Signed-off-by: Mohammad Rahimi <rahimi.mhmmd@gmail.com>
>
> I did some minor modifications and applied to thunderbolt.git/next. Please
> let me know if I missed something.
>

Looks great. Just one question:

In tb_configure_asym(), if tb_switch_set_link_width() fails, we won’t restore
the link recovery status. Is that okay?

> I tested on Intel reference hardware as well but on those link recovery is
> already disabled so it pretty much does nothing. Below are the steps that I
> followed:
>
> 1. Boot with "thunderbolt.asym_threshold=10000" so that the driver switches
> links to asymmetric already upon first DP connect.
>
> 2. Connect USB4 v2 hub.
> 3. Check link and PORT_CS_19:
>
> # tblist -v
> Domain 0 Route 0: 8087:5781 Intel Barlow Host Router
> Type: Router
> UUID: c9680000...
> Generation: USB4
> NVM version: 56.81
>
> Domain 0 Route 1: 8087:1234 Intel Barlow HUB Router
> Type: Router
> Speed (Rx/Tx): 80/80 Gb/s
> Authorized: No
> UUID: e9688780...
> Generation: USB4
> NVM version: 56.81
>
> # tbdump -r 0 -a 1 -vv -N 1 PORT_CS_19
> 0x00d3 0x0004000e 0b00000000 00000100 00000000 00001110 .... PORT_CS_19
> [00:00] 0x0 Downstream Port Reset (DPR)
> [01:01] 0x1 Request RS-FEC Gen 2 (RS2)
> [02:02] 0x1 Request RS-FEC Gen 3 (RS3)
> [03:03] 0x1 USB4 Port is Configured (PC)
> [04:04] 0x0 USB4 Port is Inter-Domain (PID)
> [16:16] 0x0 Enable Wake on Connect
> [17:17] 0x0 Enable Wake on Disconnect
> [18:18] 0x1 Enable Wake on USB4 Wake
> [19:19] 0x0 Enable Wake on Inter-Domain
> [24:24] 0x0 StartAsymmetricFlow
> [30:30] 0x0 Initiate Gen 4 Link Recovery (ILR)
> [31:31] 0x0 Enable Gen 4 Link Recovery (ELR)
>
> # tbdump -r 1 -a 1 -vv -N 1 PORT_CS_19
> 0x00d3 0x0004000e 0b00000000 00000100 00000000 00001110 .... PORT_CS_19
> [00:00] 0x0 Downstream Port Reset (DPR)
> [01:01] 0x1 Request RS-FEC Gen 2 (RS2)
> [02:02] 0x1 Request RS-FEC Gen 3 (RS3)
> [03:03] 0x1 USB4 Port is Configured (PC)
> [04:04] 0x0 USB4 Port is Inter-Domain (PID)
> [16:16] 0x0 Enable Wake on Connect
> [17:17] 0x0 Enable Wake on Disconnect
> [18:18] 0x1 Enable Wake on USB4 Wake
> [19:19] 0x0 Enable Wake on Inter-Domain
> [24:24] 0x0 StartAsymmetricFlow
> [30:30] 0x0 Initiate Gen 4 Link Recovery (ILR)
> [31:31] 0x0 Enable Gen 4 Link Recovery (ELR)
>
> 3. Connect monitor to USB4 v2 hub.
> 4. Check link and PORT_CS_19.
>
> # tblist -v
> Domain 0 Route 0: 8087:5781 Intel Barlow Host Router
> Type: Router
> UUID: c9680000...
> Generation: USB4
> NVM version: 56.81
>
> Domain 0 Route 1: 8087:1234 Intel Barlow HUB Router
> Type: Router
> Speed (Rx/Tx): 120/40 Gb/s
> Authorized: No
> UUID: e9688780...
> Generation: USB4
> NVM version: 56.81
>
> # tbdump -r 0 -a 1 -vv -N 1 PORT_CS_19
> 0x00d3 0x0004000e 0b00000000 00000100 00000000 00001110 .... PORT_CS_19
> [00:00] 0x0 Downstream Port Reset (DPR)
> [01:01] 0x1 Request RS-FEC Gen 2 (RS2)
> [02:02] 0x1 Request RS-FEC Gen 3 (RS3)
> [03:03] 0x1 USB4 Port is Configured (PC)
> [04:04] 0x0 USB4 Port is Inter-Domain (PID)
> [16:16] 0x0 Enable Wake on Connect
> [17:17] 0x0 Enable Wake on Disconnect
> [18:18] 0x1 Enable Wake on USB4 Wake
> [19:19] 0x0 Enable Wake on Inter-Domain
> [24:24] 0x0 StartAsymmetricFlow
> [30:30] 0x0 Initiate Gen 4 Link Recovery (ILR)
> [31:31] 0x0 Enable Gen 4 Link Recovery (ELR)
>
> # tbdump -r 1 -a 1 -vv -N 1 PORT_CS_19
> 0x00d3 0x0004000e 0b00000000 00000100 00000000 00001110 .... PORT_CS_19
> [00:00] 0x0 Downstream Port Reset (DPR)
> [01:01] 0x1 Request RS-FEC Gen 2 (RS2)
> [02:02] 0x1 Request RS-FEC Gen 3 (RS3)
> [03:03] 0x1 USB4 Port is Configured (PC)
> [04:04] 0x0 USB4 Port is Inter-Domain (PID)
> [16:16] 0x0 Enable Wake on Connect
> [17:17] 0x0 Enable Wake on Disconnect
> [18:18] 0x1 Enable Wake on USB4 Wake
> [19:19] 0x0 Enable Wake on Inter-Domain
> [24:24] 0x0 StartAsymmetricFlow
> [30:30] 0x0 Initiate Gen 4 Link Recovery (ILR)
> [31:31] 0x0 Enable Gen 4 Link Recovery (ELR)