Re: [PATCH] arm64: dts: rockchip: decrease rising edge time of UART2

From: Heiko Stuebner <heiko@sntech.de>
To: Katsuhiro Suzuki <katsuhiro@katsuster.net>
Cc: linux-rockchip@lists.infradead.org, linux-kernel@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH] arm64: dts: rockchip: decrease rising edge time of UART2
Date: Sun, 03 Mar 2019 14:19:40 +0100	[thread overview]
Message-ID: <1623469.Hy6pdcMFRX@phil> (raw)
In-Reply-To: <20190303122705.27094-1-katsuhiro@katsuster.net>

Hi,

Am Sonntag, 3. März 2019, 13:27:05 CET schrieb Katsuhiro Suzuki:
> This patch increases drive strength of UART2 from 3mA to 12mA for
> getting more faster rising edge.
> 
> RockPro64 is using a very high speed rate (1.5Mbps) for UART2. In
> this setting, a bit width of UART is about 667ns.
> 
> In my environment (RockPro64 UART2 with FTDI FT232RL UART-USB
> converter), falling time of RockPro64 UART2 is 40ns, but riging time
> is over 650ns. So UART receiver will get wrong data, because receiver
> read intermediate data of rising edge.
> 
> Rising time becomes 300ns from 650ns if apply this patch. This is not
> perfect solution but better than now.
> 
> Signed-off-by: Katsuhiro Suzuki <katsuhiro@katsuster.net>
> ---
>  arch/arm64/boot/dts/rockchip/rk3399.dtsi | 9 +++++++--
>  1 file changed, 7 insertions(+), 2 deletions(-)

your changing a core rk3399 property here, so I'd really like to get
input from other board stakeholders on this before applying a core
change.

Could you either include the submitters of other rk3399-boards in the
recipient list so that they're aware or limit the change to rockpro64 for
the time being (aka overriding the property in the board-dts) please?

Thanks
Heiko

> diff --git a/arch/arm64/boot/dts/rockchip/rk3399.dtsi b/arch/arm64/boot/dts/rockchip/rk3399.dtsi
> index beaa92744a64..e3c8f91ead50 100644
> --- a/arch/arm64/boot/dts/rockchip/rk3399.dtsi
> +++ b/arch/arm64/boot/dts/rockchip/rk3399.dtsi
> @@ -2000,6 +2000,11 @@
>  			drive-strength = <8>;
>  		};
>  
> +		pcfg_pull_up_12ma: pcfg-pull-up-12ma {
> +			bias-pull-up;
> +			drive-strength = <12>;
> +		};
> +
>  		pcfg_pull_up_18ma: pcfg-pull-up-18ma {
>  			bias-pull-up;
>  			drive-strength = <18>;
> @@ -2521,8 +2526,8 @@
>  		uart2c {
>  			uart2c_xfer: uart2c-xfer {
>  				rockchip,pins =
> -					<4 RK_PC3 RK_FUNC_1 &pcfg_pull_up>,
> -					<4 RK_PC4 RK_FUNC_1 &pcfg_pull_none>;
> +					<4 RK_PC3 RK_FUNC_1 &pcfg_pull_up_12ma>,
> +					<4 RK_PC4 RK_FUNC_1 &pcfg_pull_none_12ma>;
>  			};
>  		};
>  
> 

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