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

[Tony McKahan <tonymckahan@gmail.com>]

On Sun, Mar 3, 2019 at 1:45 PM Tony McKahan <tonymckahan@gmail.com> wrote:
>
> Hello Katsushiro,

And apologies for the extra "s", typing too quickly I'm afraid.
>
> On Sun, Mar 3, 2019 at 12:31 PM Katsuhiro Suzuki
> <katsuhiro@katsuster.net> wrote:
> >
> > Hello Tony,
> >
> > On 2019/03/04 0:13, Tony McKahan wrote:
> > > On Sun, Mar 3, 2019 at 9:04 AM Katsuhiro Suzuki <katsuhiro@katsuster.net> wrote:
> > >>
> > >> Hello Heiko,
> > >>
> > >> Thank you for comments.
> > >>
> > >> On 2019/03/03 22:19, Heiko Stuebner wrote:
> > >>> 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?
> > >>>
> > >>
> > >> 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.
>
> The adapter is an FTDI FT232RL breakout board, attached with some
> generic Dupont connector jumpers.
> Interesting your RockPro is showing this symptom, perhaps there is a
> cold solder joint somewhere introducing resistance?
>
> >
> > 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 measured similar on my Rock64 as well.
>
> >
> > 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.
>
> I do not think this is a bad idea generally, it simply allows for more
> available current from the interface.  I'll let others be the judge of
> that, however.
>
> >
> > 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>;
> > >>>>                       };
> > >>>>               };
> > >>>>
> > >>>>
> > >>>
> > >>>
> > >>>
> > >>>
> > >>>
> > >>>
> > >>
> > >>
> > >> _______________________________________________
> > >> Linux-rockchip mailing list
> > >> Linux-rockchip@lists.infradead.org
> > >> http://lists.infradead.org/mailman/listinfo/linux-rockchip
> > >
> > >
> >