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