From: Liviu Dudau <liviu.dudau@arm.com>
To: Andre Przywara <andre.przywara@arm.com>
Cc: Sudeep Holla <sudeep.holla@arm.com>,
Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>,
Rob Herring <robh+dt@kernel.org>,
Mark Rutland <mark.rutland@arm.com>,
linux-arm-kernel@lists.infradead.org, devicetree@vger.kernel.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH] arm64: dts: arm: juno: Fix UART frequency
Date: Tue, 19 Nov 2019 12:16:00 +0000 [thread overview]
Message-ID: <20191119121559.7grzoz2yoxhg23nf@e110455-lin.cambridge.arm.com> (raw)
In-Reply-To: <20191119120331.28243-1-andre.przywara@arm.com>
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)_/¯
next prev parent reply other threads:[~2019-11-19 12:16 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-11-19 12:03 [PATCH] arm64: dts: arm: juno: Fix UART frequency Andre Przywara
2019-11-19 12:16 ` Liviu Dudau [this message]
2019-11-25 17:43 ` Sudeep Holla
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