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Date:   Tue, 9 Nov 2021 16:08:52 +0530
From:   Vihas Mak <makvihas@...il.com>
To:     Greg KH <gregkh@...uxfoundation.org>
Cc:     arnd@...db.de, linux-kernel@...r.kernel.org,
        sudipm.mukherjee@...il.com
Subject: 

> On Tue, Nov 09, 2021 at 12:28:18AM +0530, Vihas Mak wrote:
> > Make sure the mode is a valid IEEE1284 mode.
> What is a valid mode?

The valid IEEE1284 modes are the ones defined in
<uapi/linux/parport.h>. Currently there are 10 modes. Namely nibble
mode, byte mode, ECP, ECPRLE, EPP and some specials.

> How did you test this?  And why is this needed now?  What hardware was
> working that is now not going to work with this driver?

I tested this on my local pc using a parallel port and read the
incoming data on my Raspberry PI.
I also used https://github.com/strezh/VPPSniffer. It's a simple
virtual parallel port used for debugging and sniffing.

The mainline code wasn't validating the mode when a user-space program
does a ioctl call to change the current mode. It might
create some bugs if the new mode isn't one of the IEEE1284 modes
defined in <uapi/linux/parport.h>. So it's better to throw a EINVAL
beforehand, if the mode is invalid.

> > +static int pp_validate_mode(int mode)
> bool?

My bad. Will do a v2.

Thanks,
Vihas