diff options
| author | Stephan Gerhold <stephan.gerhold@linaro.org> | 2025-04-08 20:22:47 +0300 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2025-04-11 17:58:47 +0300 |
| commit | 7094832b5ac861b0bd7ed8866c93cb15ef619996 (patch) | |
| tree | d54788e2573dfdc314fe77f9ba36ac84e41c9515 /drivers/tty | |
| parent | 0af2f6be1b4281385b618cb86ad946eded089ac8 (diff) | |
| download | linux-7094832b5ac861b0bd7ed8866c93cb15ef619996.tar.xz | |
serial: msm: Configure correct working mode before starting earlycon
The MSM UART DM controller supports different working modes, e.g. DMA or
the "single-character mode", where all reads/writes operate on a single
character rather than 4 chars (32-bit) at once. When using earlycon,
__msm_console_write() always writes 4 characters at a time, but we don't
know which mode the bootloader was using and we don't set the mode either.
This causes garbled output if the bootloader was using the single-character
mode, because only every 4th character appears in the serial console, e.g.
"[ 00oni pi 000xf0[ 00i s 5rm9(l)l s 1 1 SPMTA 7:C 5[ 00A ade k d[
00ano:ameoi .Q1B[ 00ac _idaM00080oo'"
If the bootloader was using the DMA ("DM") mode, output would likely fail
entirely. Later, when the full serial driver probes, the port is
re-initialized and output works as expected.
Fix this also for earlycon by clearing the DMEN register and
reset+re-enable the transmitter to apply the change. This ensures the
transmitter is in the expected state before writing any output.
Cc: stable <stable@kernel.org>
Fixes: 0efe72963409 ("tty: serial: msm: Add earlycon support")
Signed-off-by: Stephan Gerhold <stephan.gerhold@linaro.org>
Reviewed-by: Neil Armstrong <neil.armstrong@linaro.org>
Link: https://lore.kernel.org/r/20250408-msm-serial-earlycon-v1-1-429080127530@linaro.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'drivers/tty')
| -rw-r--r-- | drivers/tty/serial/msm_serial.c | 6 |
1 files changed, 6 insertions, 0 deletions
diff --git a/drivers/tty/serial/msm_serial.c b/drivers/tty/serial/msm_serial.c index 1b137e068444..3449945493ce 100644 --- a/drivers/tty/serial/msm_serial.c +++ b/drivers/tty/serial/msm_serial.c @@ -1746,6 +1746,12 @@ msm_serial_early_console_setup_dm(struct earlycon_device *device, if (!device->port.membase) return -ENODEV; + /* Disable DM / single-character modes */ + msm_write(&device->port, 0, UARTDM_DMEN); + msm_write(&device->port, MSM_UART_CR_CMD_RESET_RX, MSM_UART_CR); + msm_write(&device->port, MSM_UART_CR_CMD_RESET_TX, MSM_UART_CR); + msm_write(&device->port, MSM_UART_CR_TX_ENABLE, MSM_UART_CR); + device->con->write = msm_serial_early_write_dm; return 0; } |