Hi Matt,
On Tuesday, October 17, 2017 at 6:28 AM Matt Redfearn wrote:
> During set up of the early console, the earlycon driver will attempt to
> configure a baud rate, if one is set in the earlycon structure.
> Previously, of_setup_earlycon left this field as 0, ignoring any baud
> rate selected by the DT. Commit 31cb9a8575ca ("earlycon: initialise baud
> field of earlycon device structure") changed this behaviour such that
> any selected baud rate is now set. The earlycon driver must deduce the
> divisor from the configured uartclk, which of_setup_earlycon sets to
> BASE_BAUD. MIPS generic kernels do not set BASE_BAUD (there is no
> practical way to set this generically for all supported platforms), so
> when the early console is configured an incorrect divisor is calculated
> for the selected baud rate, and garbage is printed to the console during
> boot.
>
> Fix this by removing the configured baud rate from the device tree.
> This causes the early console to inherit the baud rate settings from the
> bootloader. By the time the real console is probed, the clock drivers
> necessary to calculate the divisor are enabled and the kernel can
> correctly configure the baud rate.
Sadly I think this breaks the proper console - my current understanding
is that we end up with it set to 9600 baud due to the defaults in
serial8250_console_setup(). So with your patch I see correct output from
the early console, then nothing when the proper console registers until
my userland starts a getty on ttyS0 which reconfigures it to 115200 baud.
Thanks,
Paul
> Fixes: 31cb9a8575ca ("earlycon: initialise baud field of earlycon device
> structure")
> Signed-off-by: Matt Redfearn <matt.redfearn@xxxxxxxx>
>
> ---
>
> arch/mips/boot/dts/img/boston.dts | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/mips/boot/dts/img/boston.dts
> b/arch/mips/boot/dts/img/boston.dts
> index 53bfa29a7093..179691aae7d7 100644
> --- a/arch/mips/boot/dts/img/boston.dts
> +++ b/arch/mips/boot/dts/img/boston.dts
> @@ -11,7 +11,7 @@
> compatible = "img,boston";
>
> chosen {
> - stdout-path = "uart0:115200";
> + stdout-path = "uart0";
> };
>
> aliases {
> --
> 2.7.4
