* [PATCH] arm64: dts: arm: juno: Fix UART frequency
@ 2019-11-19 12:03 Andre Przywara
2019-11-19 12:16 ` Liviu Dudau
2019-11-25 17:43 ` Sudeep Holla
0 siblings, 2 replies; 3+ messages in thread
From: Andre Przywara @ 2019-11-19 12:03 UTC (permalink / raw)
To: Liviu Dudau, Sudeep Holla, Lorenzo Pieralisi
Cc: Rob Herring, Mark Rutland, linux-arm-kernel, devicetree, linux-kernel
Older versions of the Juno *SoC* TRM [1] recommended that the UART clock
source should be 7.2738 MHz, whereas the *system* TRM [2] stated a more
correct value of 7.3728 MHz. Somehow the wrong value managed to end up in
our DT.
Doing a prime factorisation, a modulo divide by 115200 and trying
to buy a 7.2738 MHz crystal at your favourite electronics dealer suggest
that the old value was actually a typo. The actual UART clock is driven
by a PLL, configured via a parameter in some board.txt file in the
firmware, which reads 7.37 MHz (sic!).
Fix this to correct the baud rate divisor calculation on the Juno board.
Signed-off-by: Andre Przywara <andre.przywara@arm.com>
[1] http://infocenter.arm.com/help/topic/com.arm.doc.ddi0515b.b/DDI0515B_b_juno_arm_development_platform_soc_trm.pdf
[2] http://infocenter.arm.com/help/topic/com.arm.doc.100113_0000_07_en/arm_versatile_express_juno_development_platform_(v2m_juno)_technical_reference_manual_100113_0000_07_en.pdf
---
arch/arm64/boot/dts/arm/juno-clocks.dtsi | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/arch/arm64/boot/dts/arm/juno-clocks.dtsi b/arch/arm64/boot/dts/arm/juno-clocks.dtsi
index e5e265dfa902..2870b5eeb198 100644
--- a/arch/arm64/boot/dts/arm/juno-clocks.dtsi
+++ b/arch/arm64/boot/dts/arm/juno-clocks.dtsi
@@ -8,10 +8,10 @@
*/
/ {
/* SoC fixed clocks */
- soc_uartclk: refclk7273800hz {
+ soc_uartclk: refclk7372800hz {
compatible = "fixed-clock";
#clock-cells = <0>;
- clock-frequency = <7273800>;
+ clock-frequency = <7372800>;
clock-output-names = "juno:uartclk";
};
--
2.17.1
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [PATCH] arm64: dts: arm: juno: Fix UART frequency
2019-11-19 12:03 [PATCH] arm64: dts: arm: juno: Fix UART frequency Andre Przywara
@ 2019-11-19 12:16 ` Liviu Dudau
2019-11-25 17:43 ` Sudeep Holla
1 sibling, 0 replies; 3+ messages in thread
From: Liviu Dudau @ 2019-11-19 12:16 UTC (permalink / raw)
To: Andre Przywara
Cc: Sudeep Holla, Lorenzo Pieralisi, Rob Herring, Mark Rutland,
linux-arm-kernel, devicetree, linux-kernel
On Tue, Nov 19, 2019 at 12:03:31PM +0000, Andre Przywara wrote:
> Older versions of the Juno *SoC* TRM [1] recommended that the UART clock
> source should be 7.2738 MHz, whereas the *system* TRM [2] stated a more
> correct value of 7.3728 MHz. Somehow the wrong value managed to end up in
> our DT.
> Doing a prime factorisation, a modulo divide by 115200 and trying
> to buy a 7.2738 MHz crystal at your favourite electronics dealer suggest
> that the old value was actually a typo. The actual UART clock is driven
> by a PLL, configured via a parameter in some board.txt file in the
> firmware, which reads 7.37 MHz (sic!).
>
> Fix this to correct the baud rate divisor calculation on the Juno board.
>
> Signed-off-by: Andre Przywara <andre.przywara@arm.com>
>
> [1] http://infocenter.arm.com/help/topic/com.arm.doc.ddi0515b.b/DDI0515B_b_juno_arm_development_platform_soc_trm.pdf
> [2] http://infocenter.arm.com/help/topic/com.arm.doc.100113_0000_07_en/arm_versatile_express_juno_development_platform_(v2m_juno)_technical_reference_manual_100113_0000_07_en.pdf
Acked-by: Liviu Dudau <liviu.dudau@arm.com>
Best regards,
Liviu
> ---
> arch/arm64/boot/dts/arm/juno-clocks.dtsi | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/arch/arm64/boot/dts/arm/juno-clocks.dtsi b/arch/arm64/boot/dts/arm/juno-clocks.dtsi
> index e5e265dfa902..2870b5eeb198 100644
> --- a/arch/arm64/boot/dts/arm/juno-clocks.dtsi
> +++ b/arch/arm64/boot/dts/arm/juno-clocks.dtsi
> @@ -8,10 +8,10 @@
> */
> / {
> /* SoC fixed clocks */
> - soc_uartclk: refclk7273800hz {
> + soc_uartclk: refclk7372800hz {
> compatible = "fixed-clock";
> #clock-cells = <0>;
> - clock-frequency = <7273800>;
> + clock-frequency = <7372800>;
> clock-output-names = "juno:uartclk";
> };
>
> --
> 2.17.1
>
--
====================
| I would like to |
| fix the world, |
| but they're not |
| giving me the |
\ source code! /
---------------
¯\_(ツ)_/¯
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH] arm64: dts: arm: juno: Fix UART frequency
2019-11-19 12:03 [PATCH] arm64: dts: arm: juno: Fix UART frequency Andre Przywara
2019-11-19 12:16 ` Liviu Dudau
@ 2019-11-25 17:43 ` Sudeep Holla
1 sibling, 0 replies; 3+ messages in thread
From: Sudeep Holla @ 2019-11-25 17:43 UTC (permalink / raw)
To: Andre Przywara
Cc: Liviu Dudau, Lorenzo Pieralisi, Rob Herring, Mark Rutland,
linux-arm-kernel, devicetree, linux-kernel, Sudeep Holla
On Tue, Nov 19, 2019 at 12:03:31PM +0000, Andre Przywara wrote:
> Older versions of the Juno *SoC* TRM [1] recommended that the UART clock
> source should be 7.2738 MHz, whereas the *system* TRM [2] stated a more
> correct value of 7.3728 MHz. Somehow the wrong value managed to end up in
> our DT.
> Doing a prime factorisation, a modulo divide by 115200 and trying
> to buy a 7.2738 MHz crystal at your favourite electronics dealer suggest
> that the old value was actually a typo. The actual UART clock is driven
> by a PLL, configured via a parameter in some board.txt file in the
> firmware, which reads 7.37 MHz (sic!).
>
> Fix this to correct the baud rate divisor calculation on the Juno board.
>
> Signed-off-by: Andre Przywara <andre.przywara@arm.com>
>
Do we need fixes tag here ? Unless someone objects I will add and apply
this patch:
Fixes: 71f867ec130e ("arm64: Add Juno board device tree.")
--
Regards,
Sudeep
^ permalink raw reply [flat|nested] 3+ messages in thread
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2019-11-19 12:03 [PATCH] arm64: dts: arm: juno: Fix UART frequency Andre Przywara
2019-11-19 12:16 ` Liviu Dudau
2019-11-25 17:43 ` Sudeep Holla
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