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Date:   Mon, 30 Oct 2023 20:51:06 -0700
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Subject: Re: Gaps in logs while using usb-serial as a console
To:     Alan Stern <stern@rowland.harvard.edu>,
        Greg KH <gregkh@linuxfoundation.org>
Cc:     ariel marcovitch <arielmarcovitch@gmail.com>, johan@kernel.org,
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From:   Randy Dunlap <rdunlap@infradead.org>
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On 10/30/23 07:19, Alan Stern wrote:
> On Mon, Oct 30, 2023 at 09:30:15AM +0100, Greg KH wrote:
>> On Mon, Oct 30, 2023 at 10:15:30AM +0200, ariel marcovitch wrote:
>>>> Please realize that usb-serial console was the result of me loosing a
>>>> drunken bet.  It's amazing it works at all.  For "fake" devices like
>>> LOL your drunken bet was quite helpful to some people
>>> Because modern PCs come without a serial port, I wanted to use it to
>>> see early logs on my crashing kernel without having to use printk
>>> delay and things like that.
>>> I'm curious as to how kernel people debug PCs in general...
>>
>> We use a usb debug port connection (it's a special cable).

For EHCI it is a special cable. For XHCI you can use a special cable but
it is not required. (I saw a few people on LKML say that a normal data cable
works so I tested it and it does work.)

But if you want the special cable (for XHCI), this one works:
  https://www.datapro.net/products/usb-3-0-super-speed-a-a-debugging-cable.html

So I tested with both the special debug cable and a normal A-A data cable,
both with satisfactory results.

> Sometimes people use netconsole (see 
> Documentation/networking/netconsole.rst).  I don't know how common it is 
> nowadays, and it may not be quite as reliable as a debug port device, 
> but it should still work.  And it doesn't require special hardware.

It would be great if netconsole worked with wifi and not wired (ethernet).

-- 
~Randy