* [PATCH] MIPS: Boston: Fix earlycon baud rate selection
@ 2017-10-17 13:27 Matt Redfearn
2017-10-25 22:09 ` Paul Burton
0 siblings, 1 reply; 3+ messages in thread
From: Matt Redfearn @ 2017-10-17 13:27 UTC (permalink / raw)
To: Ralf Baechle
Cc: linux-mips, Matt Redfearn, devicetree, linux-kernel, Rob Herring,
Mark Rutland, Paul Burton
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.
Fixes: 31cb9a8575ca ("earlycon: initialise baud field of earlycon device structure")
Signed-off-by: Matt Redfearn <matt.redfearn@mips.com>
---
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
^ permalink raw reply related [flat|nested] 3+ messages in thread* RE: [PATCH] MIPS: Boston: Fix earlycon baud rate selection
2017-10-17 13:27 [PATCH] MIPS: Boston: Fix earlycon baud rate selection Matt Redfearn
@ 2017-10-25 22:09 ` Paul Burton
[not found] ` <0F3A6103614E5547AAE5309112E22E9102C5C4FA-8mq1oxvLakYkd5NFdqqD1Emw1/PebVxz@public.gmane.org>
0 siblings, 1 reply; 3+ messages in thread
From: Paul Burton @ 2017-10-25 22:09 UTC (permalink / raw)
To: Ralf Baechle
Cc: linux-mips@linux-mips.org, Matt Redfearn,
devicetree@vger.kernel.org, linux-kernel@vger.kernel.org,
Rob Herring, Mark Rutland, Paul Burton
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@mips.com>
>
> ---
>
> 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
^ permalink raw reply [flat|nested] 3+ messages in thread
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2017-10-17 13:27 [PATCH] MIPS: Boston: Fix earlycon baud rate selection Matt Redfearn
2017-10-25 22:09 ` Paul Burton
[not found] ` <0F3A6103614E5547AAE5309112E22E9102C5C4FA-8mq1oxvLakYkd5NFdqqD1Emw1/PebVxz@public.gmane.org>
2017-10-26 12:07 ` Matt Redfearn
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