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Tue, 21 Jul 2020 15:57:26 -0700 (PDT) Date: Tue, 21 Jul 2020 15:57:24 -0700 From: Nathan Chancellor To: Nicolas Saenz Julienne , linux-rpi-kernel@lists.infradead.org Subject: Issues attempting to use Raspberry Pi 4 serial console on mainline Message-ID: <20200721225724.GA1005852@ubuntu-n2-xlarge-x86> MIME-Version: 1.0 Content-Disposition: inline X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200721_185730_104330_7CC1C9C5 X-CRM114-Status: GOOD ( 13.73 ) 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: clang-built-linux@googlegroups.com, bcm-kernel-feedback-list@broadcom.com, linux-arm-kernel@lists.infradead.org Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org Hi all, Thank you for all of the hard work that has been done on supporting the Raspberry Pi 4 upstream. It has been a great platform so far for testing various clang technologies on actual hardware. I am investigating a panic that occurs when running a guest under KVM when clang's Shadow Call Stack is enabled and it would be handy to grab the kernel panic via serial console as the device panics and I lose my ssh connection. I picked up a USB to TTL cable and I am able to get connected with the following config.txt options and cmdline.txt options: $ head -n4 /boot/config.txt enable_uart=1 kernel=Image os_prefix=custom-mainline-arm64/ upstream_kernel=1 $ cat /boot/custom-mainline-arm64/cmdline.txt console=ttyS1,115200 console=tty1 root=PARTUUID=45a8dd8a-02 rootfstype=ext4 elevator=deadline fsck.repair=yes rootwait plymouth.ignore-serial-consoles However, when I connect to the serial console via PuTTY, I get nothing but garbage output: https://imgur.com/a/ekFlLYq As I understand it, that is due to the mini UART not being as good as a regular PL011. On the downstream kernel, one would apply 'dtoverlay=disable-bt' which would free up the first PL011 to be used as the primary UART but the device tree overlays do not work on a mainline kernel. Is there an easy way to disable Bluetooth via the device tree? If not, is there any recommended or documented way to use the mini UART successfully? I have seen information around using 'core_freq=...' but the documentation says that does not work for the Raspberry Pi 4. Any guidance or documentation that you could point me to would be much appreciated. Cheers, Nathan _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel