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

[Katsuhiro Suzuki]

Hello Tony,

On 2019/03/04 0:13, Tony McKahan wrote:
> On Sun, Mar 3, 2019 at 9:04 AM Katsuhiro Suzuki <katsuhiro@xxxxxxxxxxxxx> wrote:
> > 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.
>
> I'm pulling out other rockchip boards momentarily to see what kind of
> population we have.
>
> Note these are not all running 5.x kernels, however none of them have
> the UART2 drive levels modified to my knowledge, and regardless, none
> show over 100 ns.
>
> board:    rise/fall
>
> rk3399-roc-pc: 90ns/90ns
> rk3399-rockpro64 V2.0:  90ns/45ns
> rk3399-rockpro64 V2.1:  40ns/41ns
>
> Please make sure there's not a large amount of flux or something
> around the terminals on your board, that seems excessively high.

Thank you for valuable information. For more deeply discussion,
I tried other conditions and watch the rise/fall times.

1) Not connect
The rise/fall times are 40ns/5ns when nothing connect (impedance is
very high) to external pin of RockPro64.

What UART device are you using with RockPro64? If you use some device
with RockPro64 and board shows rise/fall times = 90ns/45ns, my device
is not suitable for RockPro64 by some reason. So it's better to drop
my patch.

2) Other SoC
I have other SoC board rk3328-rock64, Rock64 shows rise/fall times =
90ns/80ns when same UART-USB device is connected to UART pin.

I think it shows rk3399's (or RockPro64's?) drive strength is a little
weak. So it's better to increase the drive strength of UART of rk3399.

Best Regards,
Katsuhiro Suzuki

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