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

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