From 725cf89512eba9a49d447f009e0b97fdf2ae5dd6 Mon Sep 17 00:00:00 2001 From: Stephan Gerhold Date: Mon, 28 Jun 2021 10:40:09 +0200 Subject: [PATCH] serial: serial_msm: Ensure BAM/single character mode are disabled At the moment, the U-Boot serial_msm driver does not initialize the UART_DM_DMEN register with the required value. Usually this does not cause any problems, because there is Qualcomm's LK bootloader running before U-Boot which initializes the register with the correct value. It's important that this register is initialized correctly, because the U-Boot driver does not make use of the BAM/DMA or single character mode functionality of the UART controller. A different bootloader before U-Boot might initialize the register differently. For example, on DragonBoard 410c U-Boot can also be installed to the "aboot" partition (replacing LK entirely). In this case U-Boot is loaded directly by SBL, which seems to use the single-character mode for some reason. In single character mode there is always just one char in the FIFO, instead of the 4 characters expected by msm_serial_fetch(). It also causes issues with "earlycon" later in the Linux kernel, which tries to output 4 chars at once, but only the first char will be written. This causes early UART log in Linux to be corrupted like this: [ 00ano:ameoi .Q1B[ 00ac _idaM00080oo'ahani-lcle._20). 15NdNii 5 SPMSJ20:U2 [ 00rkoolmsamel [ 00Fw ]elamletopsioble [ 00ore instead of [ 0.000000] Booting Linux on physical CPU 0x0000000000 [0x410fd030] [ 0.000000] Machine model: Qualcomm Technologies, Inc. APQ 8016 SBC [ 0.000000] earlycon: msm_serial_dm0 at MMIO 0x00000000078b0000 (options '') [ 0.000000] printk: bootconsole [msm_serial_dm0] enabled Make sure to initialize UART_DM_DMEN correctly to fix this issue when loading U-Boot directly after SBL (instead of through LK). There is no functional difference when loading U-Boot through LK since LK also initializes UART_DM_DMEN to 0x0. [1] [1]: https://git.linaro.org/landing-teams/working/qualcomm/lk.git/tree/platform/msm_shared/uart_dm.c?h=dragonboard410c-LA.BR.1.2.7-03810-8x16.0-linaro3#n203 Cc: Ramon Fried Signed-off-by: Stephan Gerhold Reviewed-by: Ramon Fried --- drivers/serial/serial_msm.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/drivers/serial/serial_msm.c b/drivers/serial/serial_msm.c index d8c6c2f6b5..d8dd5c1104 100644 --- a/drivers/serial/serial_msm.c +++ b/drivers/serial/serial_msm.c @@ -23,6 +23,7 @@ /* Serial registers - this driver works in uartdm mode*/ #define UARTDM_DMRX 0x34 /* Max RX transfer length */ +#define UARTDM_DMEN 0x3C /* DMA/data-packing mode */ #define UARTDM_NCF_TX 0x40 /* Number of chars to TX */ #define UARTDM_RXFS 0x50 /* RX channel status register */ @@ -197,6 +198,9 @@ static void uart_dm_init(struct msm_serial_data *priv) writel(MSM_BOOT_UART_DM_8_N_1_MODE, priv->base + UARTDM_MR2); writel(MSM_BOOT_UART_DM_CMD_RESET_RX, priv->base + UARTDM_CR); writel(MSM_BOOT_UART_DM_CMD_RESET_TX, priv->base + UARTDM_CR); + + /* Make sure BAM/single character mode is disabled */ + writel(0x0, priv->base + UARTDM_DMEN); } static int msm_serial_probe(struct udevice *dev) { -- 2.39.5