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

[Katsuhiro Suzuki]

Hello Heiko,

Thank you for comments.

On 2019/03/03 22:19, Heiko Stuebner wrote:
> Hi,
>
> Am Sonntag, 3. MÃrz 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@xxxxxxxxxxxxx>
> > ---
> >   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?

OK, I'm adding other boards members.
by ./scripts/get_maintainer.pl arch/arm64/boot/dts/rockchip/rk3399-*.dts


RockPro64 directly connect UART2 pins of RK3399 to external connector.
I think maybe other RK3399 boards are facing same problem, but I cannot
check it because I have RockPro64 only...

I'm happy if someone tell me other boards situation.

Best Regards,
Katsuhiro Suzuki


> 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>;
> >   			};
> >   		};
> >