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From:   Sven Schnelle <svens@linux.ibm.com>
To:     Peter Zijlstra <peterz@infradead.org>
Cc:     Mathias Nyman <mathias.nyman@linux.intel.com>,
        Greg KH <gregkh@linuxfoundation.org>,
        Dave Hansen <dave.hansen@intel.com>,
        Lu Baolu <baolu.lu@linux.intel.com>, x86@kernel.org,
        linux-kernel@vger.kernel.org, linux-usb@vger.kernel.org,
        Chunfeng Yun <chunfeng.yun@mediatek.com>
Subject: Re: earlyprintk=xdbc seems broken
References: <88f466ff-a065-1e9a-4226-0abe2e71b686@linux.intel.com>
        <972a0e28-ad63-9766-88da-02743f80181b@intel.com>
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        <c2b5c9bb-1b75-bf56-3754-b5b18812d65e@linux.intel.com>
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Date:   Tue, 25 Jan 2022 14:09:18 +0100
In-Reply-To: <Ye/w/lOf4f8+8fDt@hirez.programming.kicks-ass.net> (Peter
        Zijlstra's message of "Tue, 25 Jan 2022 13:45:50 +0100")
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Peter Zijlstra <peterz@infradead.org> writes:

> Now the documentation states we need this super speed A<->A cable, but
> could you also update the documentation for usb-c ? There's a fair
> number of usb-c only devices out there now.

Stupid beginners question: Would every USB3 A-A cable work, or are the
debug cables special? I've read the RX/TX pairs have to be swapped, but
to me it looks like that's always the case?

I'm just asking because i tried to debug a before-framebuffer crash on
my Thinkpad X1, but didn't have any luck getting xdbc running. Maybe
because of the bug above. Would be nice if someone could confirm whether
that should work with every USB3 A-A cable.

Thanks,
Sven