Date:   Sun, 3 Mar 2019 13:45:29 -0500
From:   Tony McKahan <tonymckahan@...il.com>
To:     Katsuhiro Suzuki <katsuhiro@...suster.net>
Cc:     Heiko Stuebner <heiko@...ech.de>,
        Akash Gajjar <Akash_Gajjar@...tor.com>,
        Brian Norris <briannorris@...omium.org>,
        Christoph Muellner <christoph.muellner@...obroma-systems.com>,
        Dmitry Torokhov <dmitry.torokhov@...il.com>,
        Douglas Anderson <dianders@...omium.org>,
        Enric Balletbo i Serra <enric.balletbo@...labora.com>,
        Ezequiel Garcia <ezequiel@...labora.com>,
        Jakob Unterwurzacher <jakob.unterwurzacher@...obroma-systems.com>,
        Klaus Goger <klaus.goger@...obroma-systems.com>,
        Levin Du <djw@...hip.com.cn>,
        Linus Walleij <linus.walleij@...aro.org>,
        Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>,
        Matthias Brugger <mbrugger@...e.com>,
        Oskari Lemmela <oskari@...mela.net>,
        Robin Murphy <robin.murphy@....com>,
        Shawn Lin <shawn.lin@...k-chips.com>,
        Shohei Maruyama <cheat.sc.linux@...look.com>,
        Tomeu Vizoso <tomeu.vizoso@...labora.com>,
        Vicente Bergas <vicencb@...il.com>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        linux-rockchip@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH] arm64: dts: rockchip: decrease rising edge time of UART2

Hello Katsushiro,

On Sun, Mar 3, 2019 at 12:31 PM Katsuhiro Suzuki
<katsuhiro@...suster.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@...suster.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@...suster.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@...ts.infradead.org
> >> http://lists.infradead.org/mailman/listinfo/linux-rockchip
> >
> >
>

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