linux-kernel - Re: Embedded USB Debug(EUD) driver

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Date:   Sat, 7 Aug 2021 07:54:57 -0700
From:   Randy Dunlap <rdunlap@...radead.org>
To:     Subhashini Rao Beerisetty <subhashbeerisetty@...il.com>,
        Greg KH <gregkh@...uxfoundation.org>
Cc:     linux-usb@...r.kernel.org,
        kernelnewbies <kernelnewbies@...nelnewbies.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: Embedded USB Debug(EUD) driver

On 8/7/21 7:23 AM, Subhashini Rao Beerisetty wrote:
> On Sat, Jul 31, 2021 at 11:12 AM Greg KH <gregkh@...uxfoundation.org> wrote:
>>
>> On Fri, Jul 30, 2021 at 11:33:09PM +0530, Subhashini Rao Beerisetty wrote:
>>> Hi All,
>>>
>>> I'm currently looking for the Embedded USB Debug (EUD) interface driver.
>>
>> For what specific hardware?  Do you have the needed "special" cable?  We
>> have support in the kernel for some types of these cables, what kernel
>> versions have you tried that did not work for this?

> It's for MSM hardware and yes we have the "special" cable.
> I could not find the device driver for this in the mainline tree. It
> would be helpful if you could point me to the kernel tree which
> supports this feature. We will compile this suggested kernel and
> necessary drivers and then will give a try on our hardware

Hi,
See USB_SERIAL_DEBUG in drivers/usb/serial/.
That symbol builds usb_debug.c in that same directory.

It may help to read Documentation/x86/earlyprintk.rst.

My own cheat sheet (quick reference) says this: (it may or
may not help you) (it might need some updating for XHCI):
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Using USB debug port (on a USB EHCI controller)

On the system under test:

CONFIG_USB_EHCI_HCD=y

kernel command line:
	earlyprintk=dbgpN,keep

With an XHCI controller, use:
	earlyprintk=xdbcN,keep

Also add:
	console=tty0
or	console=ttyUSB0
for console output to go to the serial port.

Make sure that USB_SERIAL=y, USB_SERIAL_CONSOLE=y,
and USB_SERIAL_DEBUG=y.

------
On the logging system:
(requires CONFIG_USB_SERIAL_DEBUG=y)

Run minicom and tell it to connect to /dev/ttyUSB#.
Optionally have it log all messages to a file.

#####

-- 
~Randy