linux-kernel - Re: [PATCH v2 1/2] xhci: Add a quirk for full reset on removal

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Message-ID: <20250516083328.228813ec@foxbook>
Date: Fri, 16 May 2025 08:33:28 +0200
From: Michał Pecio <michal.pecio@...il.com>
To: Thinh Nguyen <Thinh.Nguyen@...opsys.com>
Cc: Roy Luo <royluo@...gle.com>, "mathias.nyman@...el.com"
 <mathias.nyman@...el.com>, "quic_ugoswami@...cinc.com"
 <quic_ugoswami@...cinc.com>, "gregkh@...uxfoundation.org"
 <gregkh@...uxfoundation.org>, "linux-usb@...r.kernel.org"
 <linux-usb@...r.kernel.org>, "linux-kernel@...r.kernel.org"
 <linux-kernel@...r.kernel.org>, "stable@...r.kernel.org"
 <stable@...r.kernel.org>
Subject: Re: [PATCH v2 1/2] xhci: Add a quirk for full reset on removal

On Thu, 15 May 2025 23:42:50 +0000, Thinh Nguyen wrote:
> In any case, this is basically a revert of this change:
> 6ccb83d6c497 ("usb: xhci: Implement xhci_handshake_check_state()
> helper")
> 
> Can't we just revert or fix the above patch that causes a regression?

Also note that 6ccb83d6c497 claimed to fix actual problems, so
disabling it on selected hardware could bring the old bug back:

> In some situations where xhci removal happens parallel to
> xhci_handshake, we encounter a scenario where the xhci_handshake
> can't succeed, and it polls until timeout.
> 
> If xhci_handshake runs until timeout it can on some platforms result
> in a long wait which might lead to a watchdog timeout.

But on the other hand, xhci_handshake() has long timeouts because
the handshakes themselves can take a surprisingly long time (and
sometimes still succeed), so any reliance on handshake completing
before timeout is frankly a bug in itself.

Regards,
Michal