linux-kernel - Re: [usb-serial] Support for console read from usb serial driver

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Date:   Thu, 1 Feb 2018 21:15:09 +0100
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Ivid Suvarna <ivid.suvarna@...il.com>
Cc:     USB list <linux-usb@...r.kernel.org>,
        Stanislaw Gruszka <stf_xl@...pl>,
        Peter Chen <Peter.Chen@....com>,
        Alan Stern <stern@...land.harvard.edu>,
        Mathias Nyman <mathias.nyman@...el.com>,
        Bin Liu <b-liu@...com>, Felipe Balbi <balbi@...nel.org>,
        Kernel development list <linux-kernel@...r.kernel.org>,
        kernelnewbies@...nelnewbies.org
Subject: Re: [usb-serial] Support for console read from usb serial driver

On Thu, Feb 01, 2018 at 11:52:18PM +0530, Ivid Suvarna wrote:
> Hi All,
> 
> I was going through usb serial driver console related source code
> (drivers/usb/serial/console.c) in linux kernel and came across
> "usb_console_write" function and was wondering if any usb serial
> convertor drivers were using this function? If so any pointers on how
> it is being used?

Yes, they all can use it.  Have you tried?

> Also can we implement something like "usb_console_read" which can be
> useful for interactive debugging like in kgdb. I saw kgdb using
> something like "poll_get_char and poll_put_char". I found them in most
> of serial drivers like 8250 and so on.

kgdb needs to run without interrupts enabled, which is impossible for
USB normally.  There has been external patches to get USB to work for
debugging, but that might have only been for simple keyboards.

> I am using pl2303 usb to serial convertor for getting a serial
> console. Is there any way to implement something like usb_console_read
> in usb serial drivers? Can you guys give me some pointers on this.

It should "just work" today for you.  What did you try that was not
working properly?

thanks,

greg k-h