On Mon, Jun 28, 2021 at 10:40:09AM +0200, Stephan Gerhold wrote: > 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 <rfried....@gmail.com> > Signed-off-by: Stephan Gerhold <step...@gerhold.net> > Reviewed-by: Ramon Fried <rfried....@gmail.com>
Applied to u-boot/master, thanks! -- Tom
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