linux-kernel - Re: [PATCH v3 04/12] usb: xhci: dbc: add support for Intel xHCI dbc quirk

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Date:	Tue, 17 Nov 2015 10:28:59 +0000
From:	Dmitry Malkin <DMalkin@...ecurity.com>
To:	Lu Baolu <baolu.lu@...ux.intel.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>
Subject: Re: [PATCH v3 04/12] usb: xhci: dbc: add support for Intel xHCI dbc
 quirk

On Mon, 16 Nov 2015 10:18:42 +0800, Lu Baolu wrote:
> This quirk works as well if debug host doesn't have DBC. I didn't try a
> DBC-capable debug host yet.

Hi,

I went through it again, with your v3 patch series on top of vanilla v4.3.0.

Two targets, one host, all with Intel chipset (XHCI device 0:14.0 with VID:8086).
Targets DIDs are 9c31 (8-series chipset) and 9d2f (100-series chipset).
Host DID is 8c31 (8-series).

I can only further confirm my previous observations.  The host cannot
see the target (there is no debug device) at all, until I manually
re-plug a debug cable.  Cable plugged in, prior to starting the target.

I think that trying a Hot Reset for all disconnected USB 3.0 ports on
the debug target *just before* setting DCE bit is inherently racy.

What if the number of disconnected ports changes or if someone will insert
a print statement or refactors your code?

Also sending TS2 to the debug host port will either:
 - get dropped by its hub as unsupported upstream request, or
 - get ignored due to SS.Inactive port state

Could you explain what exactly you workaround does at the low level?

--
with best regards,
Dmitry Malkin
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