From: Aleksey Makarov <amakarov.linux@gmail.com>
To: Petr Mladek <pmladek@suse.com>,
Aleksey Makarov <aleksey.makarov@linaro.org>
Cc: linux-serial@vger.kernel.org, linux-kernel@vger.kernel.org,
Sudeep Holla <sudeep.holla@arm.com>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Peter Hurley <peter@hurleysoftware.com>,
Jiri Slaby <jslaby@suse.com>, Robin Murphy <robin.murphy@arm.com>,
Steven Rostedt <rostedt@goodmis.org>,
"Nair, Jayachandran" <Jayachandran.Nair@cavium.com>,
Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Subject: Re: [PATCH v5 3/3] printk: fix double printing with earlycon
Date: Fri, 17 Mar 2017 13:32:23 +0300 [thread overview]
Message-ID: <a22a7007-1781-399e-4d75-2696db2d2e02@gmail.com> (raw)
In-Reply-To: <20170316135422.GK3977@pathway.suse.cz>
On 03/16/2017 04:54 PM, Petr Mladek wrote:
> On Thu 2017-03-16 13:36:35, Aleksey Makarov wrote:
>>
>>
>> On 03/15/2017 07:58 PM, Petr Mladek wrote:
>>> On Wed 2017-03-15 13:28:52, Aleksey Makarov wrote:
[..]
> I personally prefer v4. The braille console adds an unexpected
> twist into the code because it skips the rest of the function.
> IMHO, it is better when it is is tested separately with clear
> conditions and comments.
>
> I would personally add the following into
> kernel/printk/console_cmdline.h
>
> #define for_each_console_cmdline(c, i) \
> for (i = 0, c = console_cmdline; \
> i < MAX_CMDLINECONSOLES && c->name[0]; \
> i++, c++)
>
> It can be used in both __add_preferred_console()
> and register_console().
Ok
> Also I would add the following into kernel/printk/braille.h
>
> static inline bool
> is_braille_console(struct console_cmdline *c)
> {
> return !!c->brl_options;
> }
>
> Then the braille-specific code in register_console() might
> look like:
>
> /*
> * Braille console is handled a very special way.
> * Is is not listed in the console_drivers list.
> * Instead it registers its own keyboard and vt notifiers.
> *
> * Be careful and avoid calling c->match() here
> * because it might have side effects!
> */
> if (is_braille_console(c) &&
> match_console_name(newcon, c) &&
> _braille_register_console(newcon, c))
> return;
Yes, this is exactly what I was going to do.
> Finally, I would prefer to move
>
> newcon->flags |= CON_ENABLED;
>
> outside the match_console() function. The function will still
> have side effects because of the c->match() calls. But we should
> not make it worse. In fact, it would be great to remove side effects
> from the c->match() functions in the long term (not in this patch set).
I see the motivation but I am afraid this is not possible until
side effects are removed from newcon->match() and match_console().
The point is that match_console() also calls newcon->setup() (side effect)
and this CON_ENABLED flag indicates if this call was successful.
>> I am going to fix v5 preserving both the check for duplicates
>> and the invariant, but tell me please if you prefer the v4 approach.
>
> I guess that you planed to shuffle console_cmdline entries to keep
> the preferred console first/last. I am afraid that it won't be
> a nice code either. But I might be wrong.
You are right, I tried that, the code was awful.
Thank you
Aleksey Makarov
>>> The
>>> newcon->setup() call is called only when the console matches.
>>> AFAIK, there is only one braille console. We should be on
>>> the safe side if this one does not implement the match()
>>> callback. Or is it even more complicated?
>>
>> As you can see from the original code, the check for braille console
>> was performed in that branch of code where we missed newcon->match(),
>> so yes, it looks like braille console(s) does not have the match() method.
>> I used that in v4 to factor out matching for braille from the loop.
>
> The check for blr_options is sufficient and better.
>
> I suggest to wait at least two days until you spend to much time
> on reshuffling the code. It is possible that others would prefer
> v5 or suggest even other solution.
>
> Best Regards,
> Petr
> --
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>
next prev parent reply other threads:[~2017-03-17 10:43 UTC|newest]
Thread overview: 47+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-03-15 10:28 [PATCH v5 0/3] printk: fix double printing with earlycon Aleksey Makarov
2017-03-15 10:28 ` [PATCH v5 1/3] printk: fix name/type/scope of preferred_console var Aleksey Makarov
2017-03-15 10:28 ` [PATCH v5 2/3] printk: rename selected_console -> preferred_console Aleksey Makarov
2017-03-15 10:28 ` [PATCH v5 3/3] printk: fix double printing with earlycon Aleksey Makarov
2017-03-15 16:58 ` Petr Mladek
2017-03-16 7:30 ` Sergey Senozhatsky
2017-03-16 10:36 ` Aleksey Makarov
2017-03-16 13:54 ` Petr Mladek
2017-03-17 10:32 ` Aleksey Makarov [this message]
2017-03-17 11:43 ` [PATCH v6 " Aleksey Makarov
2017-03-17 13:34 ` Aleksey Makarov
2017-03-17 13:43 ` [PATCH v7 " Aleksey Makarov
2017-03-20 6:16 ` Sergey Senozhatsky
2017-03-20 10:03 ` [PATCH v8 " Aleksey Makarov
2017-03-27 14:14 ` Petr Mladek
2017-03-27 16:28 ` Aleksey Makarov
2017-03-28 2:04 ` Sergey Senozhatsky
2017-03-28 12:56 ` Petr Mladek
2017-03-30 5:55 ` Sergey Senozhatsky
2017-04-04 11:12 ` Petr Mladek
2017-04-05 18:26 ` Aleksey Makarov
2017-04-05 20:20 ` [PATCH v9 " Aleksey Makarov
2017-04-05 21:57 ` Andy Shevchenko
2017-04-06 4:44 ` Aleksey Makarov
2017-04-10 14:22 ` Petr Mladek
2017-04-10 18:00 ` Aleksey Makarov
2017-04-11 1:54 ` Sergey Senozhatsky
2017-04-11 7:43 ` Petr Mladek
2017-04-12 6:24 ` Aleksey Makarov
2017-05-09 8:29 ` Sabrina Dubroca
2017-05-11 8:24 ` Sergey Senozhatsky
2017-05-11 8:41 ` Sergey Senozhatsky
2017-05-11 11:32 ` Sergey Senozhatsky
2017-05-11 21:17 ` Aleksey Makarov
2017-05-12 1:11 ` Sergey Senozhatsky
2017-05-11 21:13 ` Aleksey Makarov
2017-05-12 12:57 ` Petr Mladek
2017-05-12 13:46 ` Petr Mladek
2017-05-14 21:01 ` Aleksey Makarov
2017-05-13 11:48 ` Sergey Senozhatsky
2017-05-14 20:37 ` Aleksey Makarov
2017-05-18 15:49 ` Petr Mladek
2017-05-26 9:37 ` Aleksey Makarov
2017-06-01 12:03 ` Petr Mladek
2017-06-06 14:31 ` Petr Mladek
2017-06-06 16:03 ` Petr Mladek
2017-06-07 9:13 ` Sergey Senozhatsky
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