linux-kernel - Re: Does braille console work?

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Message-ID: <6657242f-e4a9-f142-a6eb-f0c07a7d04f3@gmail.com>
Date:   Fri, 17 Mar 2017 12:00:02 +0300
From:   Aleksey Makarov <amakarov.linux@...il.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Samuel Thibault <samuel.thibault@...-lyon.org>,
        Aleksey Makarov <aleksey.makarov@...aro.org>,
        linux-serial@...r.kernel.org, Petr Mladek <pmladek@...e.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Joe Perches <joe@...ches.com>, linux-kernel@...r.kernel.org
Subject: Re: Does braille console work?



On 03/17/2017 03:53 AM, Samuel Thibault wrote:
> Hello,
> 
> Aleksey Makarov, on jeu. 16 mars 2017 17:02:53 +0300, wrote:
>> There can be 3 outcomes from this function:
>> 1) it returns NULL and does not set brl_options
>> 2) it returns NULL and set the variable pointed by str to NULL
>> 3) it returns non-NULL
> 
> Uh, that's odd indeed, the intent was that it'd return an error code
> only.
> 
>> To register a braille console (i. e. to call __add_preferred_console()
>> with non-NULL brl_options) function _braille_console_setup() should
>> return NULL and initialize brl_options. 
> 
> return 0 (as in no error), actually, in the intent.
> 
>> 1) in this case brl_options is NULL and non-braille console is registered
>> 2) kernel produces oops later in console_setup().  I reproduced it
>>    passing "console=brl=aaa" parameter to kernel, see below.
>> 3) no console is registered
>>
>> So braille console registration should not work.  What do I miss?
> 
> Nothing, the code transformation was broken :/

So the kernel contains seemingly unmaintained code that does not work
for at least 3 years.  Its parts in printk.c considerably complicate
code support.

>> So it looks like braille console has not been used for more than 3 years.
>> Should we remote it?
> 
> Please, no :)
> 
> It is indeed not often useful, since one would usually use a userland
> daemon to access the system, but when one's system does not boot
> properly or something similar, it's useful to have the braille
> console. That's just very not often useful.

Why should we keep the code which does not work?  And which is used
more than 3 years ago and usage requires patching.
I think removing it is a good idea

Thank you
Aleksey Makarov

> Samuel
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