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

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Message-ID: <va65iv2kmvqtg4ikoakdtdpproz7nlxx3hdy6biqkfci445f75@btgh44vhvuc5>
Date: Tue, 4 Feb 2025 02:35:16 +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 dear Mika.

On Tue, Feb 04, 2025 at 01:39:55PM GMT, Mika Westerberg wrote:
> Hi Again,
> 
> On Tue, Feb 04, 2025 at 01:16:25PM +0200, Mika Westerberg wrote:
> > On Mon, Feb 03, 2025 at 02:59:07PM +0200, Mika Westerberg wrote:
> > > On Mon, Feb 03, 2025 at 12:43:04PM +0000, Mohammad Rahimi wrote:
> > > > Hello again.
> > > > 
> > > > On Mon, Feb 03, 2025 at 02:39:44PM GMT, Mika Westerberg wrote:
> > > > > Hi,
> > > > > 
> > > > > On Mon, Feb 03, 2025 at 12:25:21PM +0000, Mohammad Rahimi wrote:
> > > > > > 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?
> > > > > 
> > > > > Good question :) Looking at the ECR, does it actually say anywhere that the
> > > > > CM should needs to re-enable it? I'm thinking that we could just disable it
> > > > > and be done with it?
> > > > 
> > > > Right. Thanks for clearing that up.
> > > 
> > > I'll check with the HW/FW folks still if they have any suggestions. I'll
> > > keep you updated.
> > 
> > Did not hear anything from them yet but I adjusted the patch slightly to
> > restore ELR if tb_switch_set_link_width() and also added back the check > 0
> > which I missed. Let me know if you find issues with this one. Thanks!
> 
> Okay got response now. It turns out this feature is something CM needs to
> enable if needed (e.g it is not automatically enabled by any router) and we
> don't do that which means this patch is not necessary, sorry. I'm going to
> drop it for now. Let me know if you think otherwise. Thanks!

Oh, I also overlooked that CM has full discretion to enable or disable it.
Anyway, thank you for keeping me in the loop and for all your help with this patch.