On Mon, Jun 28, 2021 at 10:04:29PM +0300, Ramon Fried wrote: > On Mon, Jun 28, 2021 at 9:59 PM Stephan Gerhold <step...@gerhold.net> wrote: > > > > On Mon, Jun 28, 2021 at 08:15:28PM +0300, Ramon Fried wrote: > > > On Mon, Jun 28, 2021 at 11:40 AM Stephan Gerhold <step...@gerhold.net> > > > 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> > > > > --- > > > > > > > > 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) > > > > { > > > > -- > > > > 2.32.0 > > > > > > > Hi. > > > This is strange, I never encountered the behaviour, and I did boot > > > Linux after U-boot without LK in the way. > > > > It happens for me if the boot flow is SBL -> U-Boot -> Linux instead of > > SBL -> LK -> U-Boot -> Linux (The latter is the suggested setup > > according to dragonboard410c_defconfig and the dragonboard410c > > readme.txt, but I wanted to eliminate LK entirely). > > > > If you tried the same, perhaps you didn't have earlycon enabled? > > It also happens only during early boot with earlycon enabled > > ("earlycon" in kernel parameters). It stops happening later on boot > > when the kernel fully re-initializes the UART controller. (The idea of > > earlycon is to reuse the existing UART configuration to report errors > > that occur very early during boot.) > > > > Thanks, > > Stephan > It's interesting, I wanted to eliminate LK entirely, but I encountered > an error I couldn't understand. > You can run U-boot compiled to 64bit and 32bit, in 64bit the boot is > stuck for some reason, and Tom refused to merge a patch where a 32bit > U-boot would boot a 64bit Linux. > Did you compile U-boot for 64 or 32 ? How far did you get ?
Ah, right. I run U-Boot in 64-bit mode. But I think I'm familiar with the problem you are talking about (Linux getting stuck when booting U-Boot directly in 64-bit mode). Basically it's a bug in the PSCI implementation on DragonBoard 410c (part of the TrustZone/tz firmware). Unless you have *something* that triggers the 32-bit -> 64-bit switch via the TZ syscalls, the PSCI implementation will boot all other CPU cores in 32-bit mode (since it does not know the switch to 64-bit has occurred). I have a workaround for this in my open-source "hyp" firmware replacement for DB410c: https://github.com/msm8916-mainline/qhypstub (The README has further detailed information about the bug and the workaround, it's a bit hard to explain shortly...) If you use this "hyp" firmware it shouldn't get stuck anymore. As another nice side effect both U-Boot and Linux will start in EL2 so you can use KVM or other hypervisors. :) Stephan