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

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Message-ID: <wxgsteiuto6qivnfttzuyw6jijs6ypcq4oyepqr6zbjgeez3ac@flvlpzswuyco>
Date: Mon, 3 Feb 2025 12:25:21 +0000
From: Mohammad Rahimi <rahimi.mhmmd@...il.com>
To: Mika Westerberg <mika.westerberg@...ux.intel.com>
Cc: andreas.noever@...il.com, michael.jamet@...el.com, 
	YehezkelShB@...il.com, linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4] thunderbolt: Disable Gen 4 Recovery on Asymmetric
 Transitions

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@...il.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)