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From: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
To: Alper Nebi Yasak <alpernebiyasak@gmail.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Jiri Slaby <jslaby@suse.com>, Petr Mladek <pmladek@suse.com>,
	Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
	linux-serial@vger.kernel.org,
	Steven Rostedt <rostedt@goodmis.org>,
	linux-arm-kernel@lists.infradead.org,
	linux-kernel@vger.kernel.org,
	Andrew Morton <akpm@linux-foundation.org>,
	Arvind Sankar <nivedita@alum.mit.edu>,
	Benjamin Herrenschmidt <benh@kernel.crashing.org>,
	"David S. Miller" <davem@davemloft.net>,
	Feng Tang <feng.tang@intel.com>
Subject: Re: [RFC PATCH v2 1/3] printk: Add function to set console to preferred console's driver
Date: Thu, 30 Apr 2020 19:46:29 +0300	[thread overview]
Message-ID: <20200430164629.GW185537@smile.fi.intel.com> (raw)
In-Reply-To: <20200430161438.17640-2-alpernebiyasak@gmail.com>

On Thu, Apr 30, 2020 at 07:14:35PM +0300, Alper Nebi Yasak wrote:
> Currently, add_preferred_console sets a preferred console, but doesn't
> actually change /dev/console to match it. That part is handled within
> register_device, where a newly registered console driver will be set as
> /dev/console if it matches the preferred console.
> 
> However, if the relevant driver is already registered, the only way to
> set it as /dev/console is by un-registering and re-registering it. An
> example is the xenfb_make_preferred_console() function:
> 
> 	console_lock();
> 	for_each_console(c) {
> 		if (!strcmp(c->name, "tty") && c->index == 0)
> 			break;
> 	}
> 	console_unlock();
> 	if (c) {
> 		unregister_console(c);
> 		c->flags |= CON_CONSDEV;
> 		c->flags &= ~CON_PRINTBUFFER; /* don't print again */
> 		register_console(c);
> 	}
> 
> The code above was introduced in commit 9e124fe16ff2 ("xen: Enable
> console tty by default in domU if it's not a dummy"). In short, it's aim
> is to set VT as the preferred console only after a working framebuffer
> is registered and thus VT is not the dummy device.
> 
> This patch introduces an update_console_to_preferred function that
> handles the necessary /dev/console change. With this change, the example
> above can be replaced with:
> 
> 	console_lock();
> 	add_preferred_console("tty", 0, NULL);
> 	update_console_to_preferred();
> 	console_unlock();
> 
> More importantly, these two calls can be moved to vt.c in order to bump
> its priority when a non-dummy backend for it is introduced, solving that
> problem in general.

Even w/o looking into the code I believe it breaks more platforms than fixes
anything. It was not first time one tries to do something about preferred
consoles and it appeared to break working configurations.

I would wait for PRINTK maintainers to tell, but to me it sounds like papering
over the real issue which you don't understand (yet).

-- 
With Best Regards,
Andy Shevchenko



  reply	other threads:[~2020-04-30 16:46 UTC|newest]

Thread overview: 19+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-04-30 16:14 [RFC PATCH v2 0/3] Prefer working VT console over SPCR and device-tree chosen stdout-path Alper Nebi Yasak
2020-04-30 16:14 ` [RFC PATCH v2 1/3] printk: Add function to set console to preferred console's driver Alper Nebi Yasak
2020-04-30 16:46   ` Andy Shevchenko [this message]
2020-05-01  1:44   ` Sergey Senozhatsky
2020-05-01 11:48     ` Alper Nebi Yasak
2020-05-13  5:35   ` Sergey Senozhatsky
2020-05-24 10:01     ` Daniel Vetter
2020-04-30 16:14 ` [RFC PATCH v2 2/3] vt: Set as preferred console when a non-dummy backend is bound Alper Nebi Yasak
2020-04-30 16:14 ` [RFC PATCH v2 3/3] printk: Preset tty0 as a pseudo-preferred console Alper Nebi Yasak
2020-04-30 16:44 ` [RFC PATCH v2 0/3] Prefer working VT console over SPCR and device-tree chosen stdout-path Andy Shevchenko
2020-04-30 19:32   ` Alper Nebi Yasak
2020-05-01  1:30 ` Sergey Senozhatsky
2020-05-01 11:08   ` Alper Nebi Yasak
2020-05-01 13:16     ` Andy Shevchenko
2020-05-01 15:07       ` Alper Nebi Yasak
2020-05-13 14:37 ` Petr Mladek
2020-05-13 22:22   ` Benjamin Herrenschmidt
2020-05-15 19:27   ` Alper Nebi Yasak
2020-05-25 13:04     ` Petr Mladek

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