From mboxrd@z Thu Jan 1 00:00:00 1970 From: zajec5@gmail.com (=?UTF-8?q?Rafa=C5=82=20Mi=C5=82ecki?=) Date: Thu, 20 Sep 2018 22:13:57 +0200 Subject: [PATCH] ARM: add serial.h and set BASE_BAUD to 0 Message-ID: <20180920201357.16426-1-zajec5@gmail.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org From: Rafa? Mi?ecki For years arm has been using serial.h from asm-generic which sets BASE_BAUD value to the (1843200 / 16). This is incorrect as: 1) This value obviously isn't correct for all devices 2) There are no device specific serial.h with CONFIG_ARCH_MULTIPLATFORM That value breaks early serial console e.g. on Broadcom Northstar boards (CONFIG_ARCH_BCM_5301X) which need BASE_BAUD = (99532800 / 16). The problem remained unnoticed until 4.14 and the commit 31cb9a8575ca0 ("earlycon: initialise baud field of earlycon device structure"). Above commit started filling "baud" in the "struct earlycon_device" (it seems to be a correct behavior) and changed behavior of the 8250/16550 early console driver. Starting with 4.14 kernel's 8250_early.c sets UART divisor if both: "uartclk" and "baud" are set. Having wrong value for BASE_BAUD (and so "uartclk") results in broken console setup. Solution to that has been introduced in commit 0ff3ab701963 ("serial: 8250_early: Only set divisor if valid clk & baud") and requires setting BASE_BAUD (and so "uartclk") to 0. A change similar to this action has been pushed for MIPS in the commit c8ec2041f549 ("MIPS: Add custom serial.h with BASE_BAUD override for generic kernel"). Another platform using 0 for BASE_BAUD is s390. Fixes: 31cb9a8575ca ("earlycon: initialise baud field of earlycon device structure") Cc: stable at vger.kernel.org # v4.14+ Signed-off-by: Rafa? Mi?ecki --- This problem has been originally reported by me in the e-mail: ns16550 earlycon baud broken on BCM5301X since commit 31cb9a8575ca0 ("earlycon: initialise baud field of earlycon device structure") https://www.spinics.net/lists/arm-kernel/msg644295.html --- arch/arm/include/asm/serial.h | 8 ++++++++ 1 file changed, 8 insertions(+) create mode 100644 arch/arm/include/asm/serial.h diff --git a/arch/arm/include/asm/serial.h b/arch/arm/include/asm/serial.h new file mode 100644 index 000000000000..e12f262290ad --- /dev/null +++ b/arch/arm/include/asm/serial.h @@ -0,0 +1,8 @@ +/* SPDX-License-Identifier: GPL-2.0 */ +#ifndef _ASM_ARM_SERIAL_H +#define _ASM_ARM_SERIAL_H + +/* ARM kernels support multiple devices so there isn't a single valid value. */ +#define BASE_BAUD 0 + +#endif /* _ASM_ARM_SERIAL_H */ -- 2.13.7