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Mon, 23 Mar 2020 03:50:07 -0700 (PDT) Subject: [RFC PATCH 2/3] vt: Set as preferred console when a non-dummy backend, is bound To: Greg Kroah-Hartman , Jiri Slaby , Petr Mladek , Sergey Senozhatsky References: <44156595-0eee-58da-4376-fd25b634d21b@gmail.com> From: Alper Nebi Yasak Message-ID: <611f42ec-194c-a121-bba1-5f0ac8e2109b@gmail.com> Date: Mon, 23 Mar 2020 13:50:03 +0300 User-Agent: Mozilla/5.0 (X11; Linux aarch64; rv:68.0) Gecko/20100101 Thunderbird/68.6.0 MIME-Version: 1.0 In-Reply-To: <44156595-0eee-58da-4376-fd25b634d21b@gmail.com> Content-Language: en-US X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200323_035010_662564_92ECAB18 X-CRM114-Status: GOOD ( 18.15 ) X-Spam-Score: -0.2 (/) X-Spam-Report: SpamAssassin version 3.4.3 on bombadil.infradead.org summary: Content analysis details: (-0.2 points) pts rule name description ---- ---------------------- -------------------------------------------------- -0.0 RCVD_IN_DNSWL_NONE RBL: Sender listed at https://www.dnswl.org/, no trust [2a00:1450:4864:20:0:0:0:141 listed in] [list.dnswl.org] -0.0 SPF_PASS SPF: sender matches SPF record 0.0 SPF_HELO_NONE SPF: HELO does not publish an SPF Record 0.0 FREEMAIL_FROM Sender email is commonly abused enduser mail provider [alpernebiyasak[at]gmail.com] -0.1 DKIM_VALID_AU Message has a valid DKIM or DK signature from author's domain -0.1 DKIM_VALID Message has at least one valid DKIM or DK signature 0.1 DKIM_SIGNED Message has a DKIM or DK signature, not necessarily valid -0.1 DKIM_VALID_EF Message has a valid DKIM or DK signature from envelope-from domain X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, Steven Rostedt Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+patchwork-linux-arm=patchwork.kernel.org@lists.infradead.org When a machine's device-tree has a "chosen" node with a "stdout-path" property that specified console is added as the preferred console by of_console_check via an add_preferred_console call. The property is quite common in kernel device-tree definitions. As far as I can tell, it is set to provide a reasonable default value for earlycon, and the (usually serial) console is set as preferred to avoid output going to VT's dummy backend instead of a working console. However, a chosen stdout-path property is included even in device-trees of systems that are designed to be used with a built-in display, e.g. several ARM Chromebooks. In these cases where CONFIG_VT_CONSOLE is enabled and no console argument is given on the kernel commandline, tty0 is still registered (presumably based on the order of of_console_check and vt's register_console calls) but ends up not being the preferred console. As a result, it is possible for early userspace prompts (encryption passphrase requests, emergency shells) to end up in a console that the user doesn't expect or even have access to. This patch tries to set tty0 as the /dev/console whenever a non-dummy backend tries to register as its default, unless the preferred console was set from the kernel commandline arguments. On a Samsung Chromebook Plus (Google Kevin, rk3399-gru-kevin.dts), boot messages are still visible on the framebuffer without this patch, but it isn't the preferred console due to the device-tree having a stdout-path property (from rk3399-gru.dtsi): $ sudo dmesg | grep -i "console\|printk" [ 0.000000] printk: bootconsole [uart0] enabled [ 0.010232] Console: colour dummy device 80x25 [ 0.015107] printk: console [tty0] enabled [ 0.019601] printk: bootconsole [uart0] disabled [ 7.145478] printk: console [ttyS2] enabled [ 9.316094] Console: switching to colour frame buffer device 300x100 $ cat /proc/consoles ttyS2 -W- (EC p a) 4:66 tty0 -WU (E ) 4:7 And on the same machine, with this patch: $ sudo dmesg | grep -i "console\|printk" [ 0.000000] printk: bootconsole [uart0] enabled [ 0.010257] Console: colour dummy device 80x25 [ 0.015132] printk: console [tty0] enabled [ 0.019626] printk: bootconsole [uart0] disabled [ 4.741120] printk: console [ttyS2] enabled [ 6.779994] Console: switching to colour frame buffer device 300x100 [ 6.836117] printk: switching to console [tty0] $ cat /proc/consoles tty0 -WU (EC ) 4:7 ttyS2 -W- (E p a) 4:66 Signed-off-by: Alper Nebi Yasak --- drivers/tty/vt/vt.c | 7 +++++++ 1 file changed, 7 insertions(+) diff --git a/drivers/tty/vt/vt.c b/drivers/tty/vt/vt.c index bbc26d73209..0fc462ae8b2 100644 --- a/drivers/tty/vt/vt.c +++ b/drivers/tty/vt/vt.c @@ -3566,6 +3566,13 @@ static int do_bind_con_driver(const struct consw *csw, int first, int last, pr_cont("to %s\n", desc); } +#ifdef CONFIG_VT_CONSOLE + if (!console_set_on_cmdline && deflt && conswitchp != &dummy_con) { + add_preferred_console("tty", 0, NULL); + update_console_to_preferred(); + } +#endif + retval = 0; err: module_put(owner);